13. Persistence and Documents.srt

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>> Stanford University. >> All right, welcome to
>> 斯坦福大学 >> 好，欢迎来到

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lecture number 13 Stanford CS193P fall of 2017 and
斯坦福 CS193P 2017-18 年秋季学期的第十三节课

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18. So we have a very which demo today, I've actually kind

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of compressed it ciz I really need to get to the slides,

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very important topic which is persistance. And so

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let me just dive right into that demo,

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and then we'll get to persistence right after that.

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So the demo here is I'm gonna take our emoji art and

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add a little way to make a text field appear

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up in our little collection view that slides around, so

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we can add more emoji to that little sliding thing. So

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how are we going to do that? Well to make this go quicker,

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here's our emoji as we left it off last time. But

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I've made a couple of little changes here. I've added two

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collection view cells. You see them right here,

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this one with the plus button. This is just a UI button,

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right here and then this one has got a UI text field.

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That's what this little,

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I don't know if you can see the light gray in there, but

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this is a text field inside here.

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That's the only thing that's in these new cells, and each

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of these cells, of course, I gave it an identifier.

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This one's called an AddEmojiButtonCell,

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and this one's called a EmojiInputCell.

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This cell is just a standard UI collection view cell.

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So if I look at it right here, you can see that its class is

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just UI collection view cell. But this one is a special

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text field collection view cell. A subclass of collection

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view cell that handles this text field a little bit.

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And so we're gonna go take a look at the code from that and

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actually add a little bit of extra code to that, cuz I want

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to show you just a kind of a trickier way to do things.

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That's not tricky, but it's a really valuable way that,

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that's a little bit advanced, so

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I wanted to make sure you learn that. All right, so

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I have these two new cells. Let's take a look at this code

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for the text field, collection view cell, that is right here,

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it's a very very simple cell, it just has an outlet

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to that text field you saw right there.

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Now notice when my outlet is set,

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I immediately set that outlet's delegate to my, me,

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myself. And I'm a UITextFieldDelegate.

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Okay remember the slides from last time. And

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so I only implemented one delegate method here which is

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textfieldShouldReturn and what it does, when you press

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the return key on the keyboard, it resigns first

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responder, which means it stops using the keyboard. And

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the keyboard disappears. So if you don't do this little thing

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right here, then when you press Return on the keyboard,

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the keyboard stays up. Okay and the cursor keeps blinking.

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Here it caused it to go away.

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And we're gonna add another

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delicate method here in a second. So now,

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remember that I have these two cells right here, right?

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The emoji button one and then the input cell right there. So

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now, let's go back to our emoji art controller code and

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look how I dealt with this, how I put this in the UI.

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Well, first of all that little plus button,

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it uses target action to send this message to my controller.

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Now notice it's sending it directly to the controller.

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If I had multiple of those plus buttons,

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they'd all be sending this message.

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But luckily I only have one so, this is perfectly fine.

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Remember that a lot of times if we have something in

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a collection in bureau table view and

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it's sending target action,

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we have it send it to a custom cell, right? Because we want

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each one to receive a special thing, but, here we can have

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things send it through the controller. Now all of this

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that plus button does is that it turns this adding emoji on.

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Because we're in the process of addingEmoji after you press

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that button. And then it reloads section zero.

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Now I have decided that I'm gonna put that plus button and

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the text field name in a different section from all

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the rest. Remember Collection Views, like Table Views,

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they have sections, so

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I'm gonna have section zero is gonna be the plus button or

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the text field, depending on whether I'm addingEmoji at

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the time and then section one is gonna be all mine.

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Emoji as I'm used to it today. So how do we implement that?

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Well, we have to say we have two sections now,

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instead of just one section. And when we get the number

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of items in a section here,

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we have to look at the section and see if it's section 0,

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then we have 1, either the plus button or the text field,

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or we have the number of emojis if it's our old,

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the old thing we used to have where it's all those emojis

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going across. Then we have to change our cell for item at.

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This is the thing that gets a cell for a given thing.

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So look at this section as well. So

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this is what this code used to look like and I just put it in

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an if the section is one then do what we were doing before.

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Otherwise if the section is zero, then if I'm adding

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emoji, I'm gonna put that text field in there. And

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if i'm not adding emoji, I'm gonna put the button in there.

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the text field are going to be exchanging places right?

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So the button and

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You press the button, it's going to change and

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switch to the text field because I'm gonna set this

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adding emoji to true and then I'm gonna reload my section.

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And that's gonna cause all of this to get called again and

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it's gonna switch back and forth. So I'm gonna have to

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put some code in here, when I switch to the text field

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to get the text out, and we're gonna talk about that. But

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before that, let me show you a couple other things I did.

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One is I want the text field, when it's there, to be very

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wide. I don't want it to be tiny like all the other cells.

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I want it to be a wide cell, so

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I overrode this method here. A collection view layout method

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called size for item at index path.

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And you return a size for an item at that path. Well,

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if I'm adding emoji and we're talking about section zero,

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then I'm going for wide buttons, otherwise,

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I'm doing the standard size I had before, and yes,

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these are blue numbers, they shouldn't be here. I should be

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calculating this based on the size of the font that the user

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chose and the accessibility slider, all that, but we don't

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have time for all that so I'm using blue numbers here. And

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then another one I overrode here is will display cell.

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That's another cool little delegate method

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in collection view.

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This is called right before it displays a cell.

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And here what I do is if I'm displaying the input cell,

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that little text field one, I make it become the first

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responder. That way when the text field comes up,

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the keyboard comes up. See why I'm doing that? So

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will display cell. Another fun collection do you think?

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I only had to do another couple other small things.

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I disabled dragging here if we're editing the emoji.

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If we're typing a new emoji, I don't let the dragging happen

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because it just messes things up

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to try to be swapping things around at the same time.

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That we're adding stuff, so I took that out of there.

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I also don't allow dropping, where's my drop code here?

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DropProposal, where is that? I can't find any in here,

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here it is. So I don't allow when you're, repositioning

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the collection items, right, the little emojis.

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I don't allow putting it into section 0. That's where

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the plus button is. I don't wanna drop smiley face for

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the bike into where the plus button is, that section. So

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I just say here that if the index path

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is section one, then I'll do this thing where I'll copy or

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move the emoji. Otherwise, I'm gonna say the drop proposal is

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cancelled, which means I can't drop there. Everyone

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cool with that? So that's all the code that I did. Now,

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the last thing, let's run and see what this looks like here.

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Here's our UI. So, here's our thing that we have so I can

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move things around. There's the plus button on the left.

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Oops. If I press that plus button, you see it gets

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replaced with the text field. And I can bring up my

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keyboard here and start typing in, some, I don't know,

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what do we got here some shoes and hats and stuff.

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And typing these things in. Now if I press the return key,

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my keyboard is gonna go away cuz I implemented that one

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text delegate method. see how it went away? But it's

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not adding the emoji, because I have not put any code

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in here that actually takes what I typed in there. And

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adds it to my scrolling list. So how am I gonna do that?

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Well that is the trick. Let's go take a look.

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And we want to essentially, in our text field right here,

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when the text field resigns being first responder, right,

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when it stops showing the text field. Then we want

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to put that in. So of course, we're gonna use this

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delegate method I talked about called TextFieldDidEndEditing.

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Editing, editing. There it is. And when this happens,

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I wanna talk back to my collection view basically and

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say add the emoji that was in my text field. But

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how do I talk back to my collection view here?

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The collection view cells don't really have a pointer to

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their collection view.

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So, it's an interesting problem to solve, and

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I'm actually gonna solve it. A lot of people would solve it

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by trying to go find the collection here and

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talk to it or something like that. But

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an actually a much easier way to do this with closures. So

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I'm create a var, public var in the cell called resignation

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handler. And it's just going to be a closure, a function

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that takes no arguments and returns no arguments.

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In fact I'm even going to make this an optional function so

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that it can be nill, doesn't have to be set.

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And when text field editing happens I'm just gonna

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call this thing, resignation handler. Might be nil so

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I'll optional chain it and call it. So I'm just calling

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that function. Now, anyone who is interested, when my text

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fields resigns can just set this closure to something. And

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that's exactly what we're gonna do back here

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in our controller. Where we load up our cell,

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which is right here. If we're doing the emoji input cell,

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which is the thing with the text fill.

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I'm just gonna say if I can let input cell equal this cell

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as a text field collection cell, which is collection view

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cell which is that cell that has that text field in it.

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Then I'm gonna set the input cells, resignation handler,

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resignation handler. Now, I'm just going to set it

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to be some closure that does what I want when that text

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field resigns to the first responder. Well, what do I

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want to do? I want to take the emoji out of it and

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put into my list, of course. So, let's just do that.

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I'm gonna set my, well, first, I'm going to say, if I can let

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text equal the input cells text fields text, so

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if you can get some text out of there.

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Then I am just going to have my emojis,

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remember that's my model right here? That's the thing that,

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oops, where is it? Shows all the emojis here,

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I'm just going to add to that thing I'm just gonna say my

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emojis equals, that text that was in the text field.

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And I'm gonna map them, all the characters in there to be

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strings, so that I have an array of strings, right? And

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I'm gonna add that to what's already there.

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So that's emojis just are the emojis we already have. And

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I'm even going to do a little trick where I'm going to

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uniquify them, uniquified. This is just a little thing

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that I put in that utilities thing which takes an array and

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makes sure all the items are unique.

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Because I don't want to have multiple smiley faces,

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multiple bikes, whatever. Now of course I get this of, hey

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you are using self implicitly here, you should put self dot.

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And every time you do that, you're gonna pause and

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say hmm, does this create a memory cycle or

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is this perhaps causing a multithreaded issue?

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Well there's no multi threading issue problem here.

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Cuz we we don't have a problem with cells being scrolled

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off and scrolled back on like you have in your homework. But

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there is a memory cycle here. You see how

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there's a memory cycle because self is the collection,

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is our selfish view-controller.

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And we point to our collection view.

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Our collection view points to its cells, of course. Its cell

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points to this closure. And this closure points back

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to ourself. So it's going around and round. So

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we have to break this with weak self. And

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then make all our selfs here be question mark.

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00:11:33,893 --> 00:11:37,495
This is a self also. It can be self exclamation point because

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00:11:37,563 --> 00:11:40,231
we won't get there if this is nil. So, that's good,

236
00:11:40,300 --> 00:11:42,466
but there's actually another one in here.

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00:11:42,535 --> 00:11:44,869
Sometimes, just because it tells you about self,

238
00:11:44,938 --> 00:11:46,704
doesn't mean there might not be other ones in there.

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00:11:46,773 --> 00:11:50,441
And there is another one, it's this. This var is the input

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00:11:50,510 --> 00:11:52,877
cell and I'm using it inside this closure,

241
00:11:52,945 --> 00:11:55,546
which will capture it. And yet it is pointing

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00:11:55,615 --> 00:11:59,117
back to the closure through its resignation handler,

243
00:11:59,185 --> 00:12:01,552
so this has to be broken as well.

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00:12:01,621 --> 00:12:06,857
Now this one we can broke, break, with unowned because

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00:12:06,926 --> 00:12:10,995
we know we would never be in this closure executing it,

246
00:12:11,063 --> 00:12:15,165
if this were nil. Because by definition, we're executing

247
00:12:15,234 --> 00:12:18,603
its resignationHandler, so we can use unowned, in this case,

248
00:12:18,671 --> 00:12:21,973
to do that. And what else do we need to do here? Well, we

249
00:12:22,042 --> 00:12:25,376
just need to stop saying that we are adding emoji, because

250
00:12:25,445 --> 00:12:28,612
we're not, right, we've finished adding emoji here.

251
00:12:28,681 --> 00:12:32,917
And then, we're gonna have to ask our emoji collection view

252
00:12:32,986 --> 00:12:36,287
to reload data. Why do we need to reload data?

253
00:12:36,356 --> 00:12:38,656
Cuz we just added emoji to our model and

254
00:12:38,725 --> 00:12:42,393
anytime you change the model you need to update your table.

255
00:12:42,461 --> 00:12:44,228
So I'm gonna reload and cause it to go back,

256
00:12:44,297 --> 00:12:47,031
look at my new model, call all those functions,

257
00:12:47,099 --> 00:12:50,468
all these functions right here, reload everything.

258
00:12:50,537 --> 00:12:52,837
It's also gonna nicely reload section zero and

259
00:12:52,905 --> 00:12:56,774
put the button back because I set this back to false. So

260
00:12:56,843 --> 00:12:58,409
let's see all of this in action.

261
00:13:06,385 --> 00:13:09,053
Here we go. So, we've got this, we can still

262
00:13:09,121 --> 00:13:12,556
scroll around, normally. We can reposition these things.

263
00:13:12,625 --> 00:13:14,625
It won't let us put it in section 0,

264
00:13:14,694 --> 00:13:18,062
that's good. We hit plus It brings up the text field.

265
00:13:18,131 --> 00:13:19,363
It reloaded that section and

266
00:13:19,432 --> 00:13:22,467
put the text field because we are adding a module right now.

267
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Can bring up my keyboard down here, let's put some

268
00:13:26,872 --> 00:13:29,373
sea creatures in here. I'm just gonna do that. Now,

269
00:13:29,442 --> 00:13:32,677
I'm gonna hit return which gonna dismiss my keyboard

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because of that resign first responder that put in there.

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And since that's gonna end editing,

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00:13:36,549 --> 00:13:41,485
it's gonna add this emoji to our list. See that? Their

273
00:13:41,554 --> 00:13:44,822
they are at the beginning. And we can do the same thing here.

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Maybe I will add, I don't know,

275
00:13:46,826 --> 00:13:49,626
some farm animals here. And this time I'm not

276
00:13:49,695 --> 00:13:52,229
gonna return, I'm actually going to dismiss my keyboard

277
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by pressing the thing in the lower right corner.

278
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You see that thing, that says keyboard go away. Ready,

279
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boom and now it added those. So that' it,

280
00:14:02,041 --> 00:14:05,542
that's text field. Sorry we had to rush, kinda rush that,

281
00:14:05,611 --> 00:14:08,379
but we, again, we got a lot of other stuff to cover. And I'll

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00:14:08,447 --> 00:14:10,815
be posting this code, so you can look at it in detail and

283
00:14:10,884 --> 00:14:12,549
see. I showed you all the changes we made,

284
00:14:12,618 --> 00:14:14,351
I just didn't type them all in,

285
00:14:14,420 --> 00:14:20,491
as we went along. All right, back to the slides right here.

286
00:14:20,559 --> 00:14:23,160
Let's get to our main topic today, which is persistence.

287
00:14:23,229 --> 00:14:26,764
By persistence, I mean making things stick around, right?

288
00:14:26,833 --> 00:14:29,333
The user inputs some stuff, they create an emoji art

289
00:14:29,402 --> 00:14:31,836
document or something like that. And you, of course,

290
00:14:31,904 --> 00:14:33,771
want those things to stay around you don't want them to

291
00:14:33,840 --> 00:14:36,040
disappear every time you run the app. Which is the case in

292
00:14:36,108 --> 00:14:38,042
your homework and the case of emoji art right now,

293
00:14:38,111 --> 00:14:40,545
which is kinda useless. So there's a lot of ways to

294
00:14:40,614 --> 00:14:42,313
make things persistent as you can see so

295
00:14:42,382 --> 00:14:44,982
let's dive right in and talk about all of them.

296
00:14:45,051 --> 00:14:47,885
Now,some of them I'm only gonna cover a little bit and

297
00:14:47,953 --> 00:14:50,888
some of them I'm gonna cover in depth. The first one here

298
00:14:50,956 --> 00:14:54,525
is UserDefault, now this one is super duper simple,

299
00:14:54,594 --> 00:14:58,329
it's kind like the dictionary that persists, right?

300
00:14:58,398 --> 00:15:00,698
You put things in this dictionary with keys and

301
00:15:00,767 --> 00:15:03,200
values and when you run your app the next time,

302
00:15:03,269 --> 00:15:07,671
they're still there. The only restriction on that though,

303
00:15:07,740 --> 00:15:10,207
is that the only things you can put in this dictionary

304
00:15:10,276 --> 00:15:12,910
thing is property lists.

305
00:15:12,979 --> 00:15:14,912
Okay now a property list is not a type, or

306
00:15:14,981 --> 00:15:17,582
anything like that, it's just a concept.

307
00:15:17,650 --> 00:15:19,817
A property list is any combination,

308
00:15:19,886 --> 00:15:23,520
any data structure, that is any combination of only array,

309
00:15:23,589 --> 00:15:27,158
dictionary, string, date, data or a number like bloat,

310
00:15:27,227 --> 00:15:30,361
hint or double. Okay that's what we call a property list.

311
00:15:30,430 --> 00:15:33,030
And that's the only thing you can put in this little

312
00:15:33,099 --> 00:15:36,067
lightweight database called UserDefaults, all right?

313
00:15:36,135 --> 00:15:39,037
So what does the API look like, to put things in there?

314
00:15:39,105 --> 00:15:42,639
Very simple, it's got two main methods here, set,

315
00:15:42,708 --> 00:15:46,244
with a property list as the argument for a key.

316
00:15:46,312 --> 00:15:50,648
And then object for a key that returns a property list.

317
00:15:50,717 --> 00:15:52,649
The reason that's an NE right there is that there's really

318
00:15:52,718 --> 00:15:55,453
no other type that would represent a Property List, and

319
00:15:55,522 --> 00:15:57,121
this is an Objective-C API.

320
00:15:57,190 --> 00:16:01,826
But that NE has to be a thing that is a Property List. So

321
00:16:01,895 --> 00:16:04,362
it could be an int. It could be an array of strings.

322
00:16:04,430 --> 00:16:06,531
It could be a dictionary whose keys are strings and

323
00:16:06,599 --> 00:16:08,733
whose values are arrays of doubles.

324
00:16:08,801 --> 00:16:11,502
Those would all be considered property lists. But

325
00:16:11,571 --> 00:16:15,572
an array of CG float? Not a property list,

326
00:16:15,641 --> 00:16:21,445
because a CG float is not a property list. All right,

327
00:16:21,514 --> 00:16:23,213
so how do you read and write this stuff?

328
00:16:23,282 --> 00:16:25,449
How do you access this? How do you call those methods? Well,

329
00:16:25,517 --> 00:16:29,419
we don't actually create a different UserDefaults thing.

330
00:16:29,488 --> 00:16:32,156
You can, but we don't usually do that. We instead used

331
00:16:32,225 --> 00:16:34,925
a shared one we get by saying UserDefaults.standard.

332
00:16:34,994 --> 00:16:39,063
Standard is a static bar in the user's evolved class, and

333
00:16:39,131 --> 00:16:42,533
it returns to this shared UserDefaults thing. And

334
00:16:42,601 --> 00:16:45,769
then we just set call set on it to set values, and we can

335
00:16:45,838 --> 00:16:50,774
call object uptight or forKey rather, to get things back.

336
00:16:50,843 --> 00:16:52,476
And so here's a bunch of examples of sets.

337
00:16:52,545 --> 00:16:53,844
Notice I can just set a float,

338
00:16:53,913 --> 00:16:54,745
because that's a property list.

339
00:16:54,814 --> 00:16:57,281
I can set an array of ints, that's a property list.

340
00:16:57,350 --> 00:16:59,717
I can also set nil, because it's an Any?, and

341
00:16:59,785 --> 00:17:02,787
that means clear out any value for

342
00:17:02,855 --> 00:17:08,626
this key. And there's some convenience methods for

343
00:17:08,694 --> 00:17:11,328
getting things out, right, cuz if you do object for

344
00:17:11,397 --> 00:17:14,731
key, what type are you gonna get back? An any, which means

345
00:17:14,800 --> 00:17:18,503
you're gonna have to use as to turn it into something. Well,

346
00:17:18,571 --> 00:17:20,405
to save you that they have some methods and

347
00:17:20,473 --> 00:17:23,207
they're like double forKey, array forKey and

348
00:17:23,275 --> 00:17:26,944
those will return you that type. Now, for example,

349
00:17:27,013 --> 00:17:30,248
double forKey, if the thing in there is not a double,

350
00:17:30,316 --> 00:17:33,117
it's just gonna return 0. Cuz it's not a question mark,

351
00:17:33,186 --> 00:17:36,254
unfortunately, it's just double. And

352
00:17:36,322 --> 00:17:39,056
similarly, an array forKey, if the thing in there,

353
00:17:39,124 --> 00:17:41,792
if that key is not an array, it's gonna return nil,

354
00:17:41,861 --> 00:17:44,594
because that is an optional array. So these little things,

355
00:17:44,663 --> 00:17:45,996
these conveniences try to help you but

356
00:17:46,065 --> 00:17:47,832
they're only gonna help you as much as they can.

357
00:17:47,901 --> 00:17:50,033
If you put the wrong types in there, obviously,

358
00:17:50,102 --> 00:17:53,504
they can't do the right thing. When am I ever gonna use this

359
00:17:53,573 --> 00:17:55,640
thing? This thing is really only for

360
00:17:55,708 --> 00:17:59,010
lightweight stuff like settings, preferences,

361
00:17:59,078 --> 00:18:01,278
that kinda stuff. You wouldn't store documents or

362
00:18:01,347 --> 00:18:05,082
any kind of serious user data in there with user defaults.

363
00:18:05,151 --> 00:18:08,318
Now saving the database, the database is autosaved for

364
00:18:08,387 --> 00:18:10,988
you. So you really don't have to save it. But sometimes you

365
00:18:11,056 --> 00:18:13,524
want to, most notably when you're in debugging and

366
00:18:13,593 --> 00:18:15,560
you're hitting stop in the debugger all the time.

367
00:18:15,628 --> 00:18:18,528
Sometimes you'll stop it before it gets a chance to

368
00:18:18,597 --> 00:18:20,431
save. So if you wanna explicitly save,

369
00:18:20,500 --> 00:18:23,133
you can use this method synchronize, which will save

370
00:18:23,202 --> 00:18:25,303
it. It returns a bool whether it was successful, although I

371
00:18:25,371 --> 00:18:27,204
don't know what you're gonna do if it wasn't successful.

372
00:18:27,272 --> 00:18:28,772
I guess try again in a little bit.

373
00:18:28,841 --> 00:18:32,242
But we usually don't look at the return value of this.

374
00:18:32,311 --> 00:18:34,979
We just say synchronize. So a lot of times people will put

375
00:18:35,047 --> 00:18:37,214
synchronize in there because they're doing the debugger,

376
00:18:37,283 --> 00:18:38,882
and they're hitting stop all the time,

377
00:18:38,951 --> 00:18:41,452
and it didn't save them, and then they run it again. So

378
00:18:41,521 --> 00:18:42,787
you can feel free to do that if you want.

379
00:18:42,855 --> 00:18:46,858
It's pretty lightweight to do synchronize. All right, so

380
00:18:46,926 --> 00:18:49,927
that's the first one. The second way to make

381
00:18:49,996 --> 00:18:53,564
things persistent is called archiving. So the problem with

382
00:18:53,633 --> 00:18:56,099
user defaults, first of all, only small things.

383
00:18:56,168 --> 00:18:59,236
Second of all, has to be property lists. What if I have

384
00:18:59,304 --> 00:19:03,173
some data structure that I wanna store, that's big and or

385
00:19:03,242 --> 00:19:06,943
has things other than property lists in it. And to do that

386
00:19:07,012 --> 00:19:10,247
I'm gonna use archiving. Now there's two mechanisms for

387
00:19:10,316 --> 00:19:14,451
archiving, an old way, and a new for iOS 11 way.

388
00:19:14,520 --> 00:19:17,154
And of course, I'm gonna talk in detail about the new for

389
00:19:17,223 --> 00:19:19,857
iOS 11 way, because the old way obviously wasn't good

390
00:19:19,926 --> 00:19:22,593
enough. They came up with a new one in iOS 11.

391
00:19:22,661 --> 00:19:24,461
But they're very, very similar in some ways.

392
00:19:24,530 --> 00:19:26,831
It's just that the new way is a lot more automatic, and

393
00:19:26,899 --> 00:19:29,933
a lot less code to write. So let's talk about these two

394
00:19:30,002 --> 00:19:32,536
ways. The old way is called NS Coder.

395
00:19:32,605 --> 00:19:35,639
So NS Coder is a protocol. And

396
00:19:35,708 --> 00:19:39,677
essentially NS Coder boils down to having every single

397
00:19:39,746 --> 00:19:43,947
object in the object graph that you want to save, or

398
00:19:44,016 --> 00:19:47,717
whatever, make persistent, implement these two things.

399
00:19:47,786 --> 00:19:49,987
A function called encode with a coder.

400
00:19:50,056 --> 00:19:53,323
So that NS coder kind of like is a dictionary thing,

401
00:19:53,392 --> 00:19:56,394
you can set values in there. And then init from coder.

402
00:19:56,462 --> 00:19:58,729
It's gonna potentially give you that dictionary back and

403
00:19:58,798 --> 00:20:02,199
you gotta initialize the object. So it's very simple.

404
00:20:02,268 --> 00:20:05,102
You're just gonna have encode sent to every single object in

405
00:20:05,170 --> 00:20:08,038
the object graph. And it's gonna put itself like in a big

406
00:20:08,107 --> 00:20:10,374
dictionary. And then when you wanna bring it back to life,

407
00:20:10,443 --> 00:20:13,110
you start telling init with the coder and

408
00:20:13,179 --> 00:20:15,112
they all have to initialize themselves.

409
00:20:15,181 --> 00:20:19,683
This is how storyboards are saved. So view Controller,

410
00:20:19,752 --> 00:20:22,653
UI View, UI Label Button, all of them implement

411
00:20:22,722 --> 00:20:26,089
both of these things in code and init from coder. And

412
00:20:26,158 --> 00:20:28,759
somebody went to a painstaking amount of work to implement

413
00:20:28,828 --> 00:20:31,028
that for every possible thing that can be in a storyboard.

414
00:20:31,097 --> 00:20:34,465
It's amazing how much work that actually took. So

415
00:20:34,533 --> 00:20:37,467
that's great, you have this encoding, encoding and

416
00:20:37,536 --> 00:20:39,503
decoding ability. What do you do with it?

417
00:20:39,571 --> 00:20:42,172
Well, what you almost always do with it is you turn this

418
00:20:42,241 --> 00:20:46,476
thing into a data. Remember our friend data, bag of bits,

419
00:20:46,545 --> 00:20:49,146
that little struct? You turn into a data, and then you

420
00:20:49,214 --> 00:20:50,680
can store a data in a file system.

421
00:20:50,749 --> 00:20:51,882
Cuz as you're gonna learn,

422
00:20:51,951 --> 00:20:54,552
that's how we interact with the file system. We store and

423
00:20:54,620 --> 00:20:58,923
read datas. So how do you take a big object graph, where

424
00:20:58,991 --> 00:21:01,191
every single object in there implements these two things,

425
00:21:01,260 --> 00:21:04,395
and turn it into a data? You do it with the class NS keyed

426
00:21:04,463 --> 00:21:08,131
archiver. So NS keyed archiver just takes an object that

427
00:21:08,200 --> 00:21:10,934
it and everything it points to implements these two things,

428
00:21:11,003 --> 00:21:14,338
and it gives you back a data that has taken the whole

429
00:21:14,407 --> 00:21:17,074
object graph, and collected it up into a data.

430
00:21:17,143 --> 00:21:20,143
And similarly, if you give it back a data like that,

431
00:21:20,212 --> 00:21:21,612
to NS keyed unarchiver,

432
00:21:21,681 --> 00:21:25,182
the unarchiver then it will turn it back into the objects

433
00:21:25,250 --> 00:21:27,751
by calling that init. Is everyone cool with how we

434
00:21:27,820 --> 00:21:30,654
do that? This is a lot of work to make this mechanism work

435
00:21:30,722 --> 00:21:32,522
because you've gotta implement those two things for

436
00:21:32,591 --> 00:21:34,624
every single object in there. So

437
00:21:34,693 --> 00:21:36,660
let's talk about the new way, which is quite similar.

438
00:21:36,729 --> 00:21:39,730
It's called Codable. And Codable is a protocol,

439
00:21:39,798 --> 00:21:43,366
it's actually two protocols, D-Codable and N-Codable. And

440
00:21:43,435 --> 00:21:46,937
it works the same kind of way. You still have init and

441
00:21:47,006 --> 00:21:48,339
you still have an encode thing.

442
00:21:48,407 --> 00:21:51,275
The difference is Swift and the runtime, and, and

443
00:21:51,343 --> 00:21:54,445
the foundation will implement those two methods for you,

444
00:21:54,513 --> 00:21:57,547
almost all the time. It just kind of implements them for

445
00:21:57,616 --> 00:21:59,283
free, so you don't have to do anything.

446
00:21:59,352 --> 00:22:02,920
So as long as you are using kind of basic types in Swift,

447
00:22:02,989 --> 00:22:05,222
including all the things that you see on this slide,

448
00:22:05,291 --> 00:22:07,891
it just all magically works. So

449
00:22:07,960 --> 00:22:11,562
I'm gonna show you both how we then take an object graph and

450
00:22:11,631 --> 00:22:13,264
turn it into a data with this mechanism,

451
00:22:13,332 --> 00:22:15,732
which is slightly different than the key archiver thing.

452
00:22:15,801 --> 00:22:17,701
And I'm also gonna show you what it looks like to make

453
00:22:17,770 --> 00:22:21,004
something Codable, cuz to make it to do this, it has to be

454
00:22:21,073 --> 00:22:23,139
Codable. It has to implement Codable. So let's look at

455
00:22:23,208 --> 00:22:26,210
those. First let's look at how we turn it into a data. Here,

456
00:22:26,278 --> 00:22:29,346
instead of turning it into just an arbitrary blob of data

457
00:22:29,415 --> 00:22:32,449
that we don't know what it is, we actually encode it to

458
00:22:32,518 --> 00:22:36,019
a known format like JSON. Everyone know what JSON is?

459
00:22:36,088 --> 00:22:38,221
It's essentially just like this text format for

460
00:22:38,290 --> 00:22:40,925
describing things on the Internet, passing data around.

461
00:22:40,993 --> 00:22:44,561
And so JSON is a well-known format, and we can turn that

462
00:22:44,630 --> 00:22:47,365
big object graph into a description of it,

463
00:22:47,433 --> 00:22:50,667
that is JSON, amazingly. And there's another

464
00:22:50,736 --> 00:22:53,770
encoder that can do this, that does property list, so.

465
00:22:53,839 --> 00:22:56,073
This whole thing I was telling you about UserDefaults,

466
00:22:56,142 --> 00:22:58,575
where everything's an array of strings or dates or numbers,

467
00:22:58,644 --> 00:23:00,711
you can also turn it into something like that.

468
00:23:00,779 --> 00:23:03,713
Those are the two encoders that come with iOS. And

469
00:23:03,782 --> 00:23:04,848
how do you do this? Well,

470
00:23:04,917 --> 00:23:08,151
you just have your object that's of mytype,

471
00:23:08,220 --> 00:23:11,922
some type that you define. That type has to be Codable.

472
00:23:11,990 --> 00:23:14,591
And as long as it's Codable and everything that it wants

473
00:23:14,660 --> 00:23:18,061
to be archived inside of it is Codable, then you can say JSON

474
00:23:18,130 --> 00:23:22,899
data equals try to JSON encode that object. And it's

475
00:23:22,968 --> 00:23:25,468
gonna give you back a data blob, and in that data blob

476
00:23:25,537 --> 00:23:29,206
is a JSON representation of your entire object graph,

477
00:23:29,274 --> 00:23:33,143
which is pretty incredible. Now notice this does throw,

478
00:23:33,212 --> 00:23:36,146
it's unlikely to throw when you're encoding, but it could

479
00:23:36,215 --> 00:23:39,383
possibly have something where first, I don't know why, but

480
00:23:39,452 --> 00:23:43,153
it couldn't encode it, it's possible it could throw.

481
00:23:43,222 --> 00:23:45,956
By the way, if you have a data Blob that's JSON,

482
00:23:46,025 --> 00:23:49,292
you might wanna look at it as a string. With JSON it's

483
00:23:49,361 --> 00:23:52,929
always encoded as utf8. That's the string encoding it uses.

484
00:23:52,998 --> 00:23:55,666
So you can always just take a data Blob like jsonData and

485
00:23:55,735 --> 00:23:58,669
from that previous line there and create a string with it.

486
00:23:58,737 --> 00:24:00,938
And all that string needs to know is what's the encoding?

487
00:24:01,007 --> 00:24:06,677
You say it's .utf8. Which is Unicode 8bit encoding.

488
00:24:06,746 --> 00:24:09,546
All right, now, what if you have a JSON representation of

489
00:24:09,615 --> 00:24:10,881
your whole object graph and

490
00:24:10,950 --> 00:24:13,116
you wanna create your object graph out of it?

491
00:24:13,185 --> 00:24:16,520
Well you just use a JSON decoder and say decode.

492
00:24:16,588 --> 00:24:20,024
Well then all you have to do here is specify The class or

493
00:24:20,092 --> 00:24:22,625
struct of the top level thing in that JSON,

494
00:24:22,694 --> 00:24:26,396
represented by that JSON. And give it the JSON data blob and

495
00:24:26,465 --> 00:24:28,865
it will decode it. Now this also throws and

496
00:24:28,934 --> 00:24:31,769
this is more likely to throw. Maybe your JSON data is

497
00:24:31,837 --> 00:24:35,639
corrupted or malformed or something like that. And

498
00:24:35,708 --> 00:24:38,175
it quite possible to make this all work, where you're

499
00:24:38,243 --> 00:24:41,144
using some standard JSON from some website out there and

500
00:24:41,213 --> 00:24:43,780
you're converting it to objects in your code.

501
00:24:43,849 --> 00:24:45,582
Where you make it do a one to one mapping.

502
00:24:45,651 --> 00:24:48,686
And so maybe the website you went to had an error and

503
00:24:48,754 --> 00:24:52,856
they generated bad JSON or something, so this could throw

504
00:24:52,924 --> 00:24:55,626
here. And let's talk, we'll talk a little about that in

505
00:24:55,694 --> 00:24:58,862
a second and what to do with that thing throwing.

506
00:24:58,931 --> 00:25:03,133
Notice that JSON is the opposite of "strongly typed".

507
00:25:03,202 --> 00:25:07,237
Like a date in JSON is just a string in some format, right?

508
00:25:07,306 --> 00:25:11,041
There's no such concept as a date type in JSON. So this

509
00:25:11,109 --> 00:25:14,444
decoder is quite configurable, so you can specify things

510
00:25:14,513 --> 00:25:18,615
like, what is the strategy to decode what should be a date?

511
00:25:18,683 --> 00:25:20,166
what format are dates stored in in this JSON file? So you

512
00:25:20,167 --> 00:25:21,650
In other words,

513
00:25:21,720 --> 00:25:25,055
can specify those kinda things to configure the decoder to be

514
00:25:25,124 --> 00:25:29,325
able to figure out this JSON representation. All right,

515
00:25:29,394 --> 00:25:32,429
now I talked about throwing errors. Here, for example,

516
00:25:32,498 --> 00:25:36,232
I'm catching a error that was thrown by this decoder.

517
00:25:36,301 --> 00:25:38,101
And the reason I'm showing this actually is not because

518
00:25:38,170 --> 00:25:40,404
you're going to do this. You're unlikely to actually

519
00:25:40,472 --> 00:25:43,173
catch these decoding errors and do anything about them.

520
00:25:43,242 --> 00:25:45,409
Unless maybe you're debugging your own JSON format,

521
00:25:45,478 --> 00:25:47,744
you wanna see where you made a mistake or something.

522
00:25:47,813 --> 00:25:50,147
But I wanted to show you here what it looks like to catch

523
00:25:50,215 --> 00:25:54,951
an error that is thrown that's an enum. Cuz remember that

524
00:25:55,020 --> 00:25:58,154
anything can be thrown. You can throw any kind of thing as

525
00:25:58,223 --> 00:26:00,557
an error. All it has to do is implement the protocol error,

526
00:26:00,625 --> 00:26:03,493
which is really nothing, so you can throw anything.

527
00:26:03,562 --> 00:26:06,529
So a lot of times things will throw an enum. And when they

528
00:26:06,598 --> 00:26:09,366
throw the enum, you can do the same thing we do with switch,

529
00:26:09,435 --> 00:26:11,468
which is to grab the associated values out.

530
00:26:11,536 --> 00:26:15,739
So you see how that really works great for errors, right?

531
00:26:15,808 --> 00:26:18,007
So you're catching the key not found error and

532
00:26:18,076 --> 00:26:19,376
you're grabbing the associated value,

533
00:26:19,444 --> 00:26:23,279
which is, one of which is the key that was not found. So

534
00:26:23,348 --> 00:26:25,816
this is a common thing to do, is to throw an enum and

535
00:26:25,885 --> 00:26:28,084
then in your catch you just catch the cases and

536
00:26:28,153 --> 00:26:31,956
you're allowed to do this same kind of grab the associated

537
00:26:32,024 --> 00:26:37,194
value as you can do with switch. All right,

538
00:26:37,263 --> 00:26:39,896
so let's look at an example of making something be codable.

539
00:26:39,965 --> 00:26:42,399
So I've got my struct MyType here. And

540
00:26:42,468 --> 00:26:44,367
it's got a date in it, a string, and

541
00:26:44,436 --> 00:26:46,837
then it's got some other bar which is some other type

542
00:26:46,906 --> 00:26:49,372
not shown here. And to make it codable,

543
00:26:49,441 --> 00:26:53,743
all I have to do is say colon codable. If I say that it's

544
00:26:53,812 --> 00:26:58,215
codable, then it is codable. Unless it or something inside

545
00:26:58,284 --> 00:27:01,484
of it can't be coded automatically by swift. So

546
00:27:01,553 --> 00:27:03,921
it's not one of those things that I showed you on the first

547
00:27:03,989 --> 00:27:07,157
slide there. So here, date is definitely codable,

548
00:27:07,225 --> 00:27:08,892
string is codable, and presumably,

549
00:27:08,961 --> 00:27:12,462
some other type has made itself codable as well. And

550
00:27:12,531 --> 00:27:15,666
so, this thing is now codable, and that's all I have to do.

551
00:27:15,734 --> 00:27:18,301
A lot easier that implementing init and encode for

552
00:27:18,370 --> 00:27:21,438
every single object in there. We just say it's codable, and

553
00:27:21,507 --> 00:27:24,274
it is. And the JSON that would be generated from using that

554
00:27:24,343 --> 00:27:26,710
JSON encoder would look something like this, right?

555
00:27:26,778 --> 00:27:29,846
someDate, which is the same name as the var, colon, and

556
00:27:29,915 --> 00:27:32,949
then the date in some encoding strategy that we decide.

557
00:27:33,018 --> 00:27:36,486
And then "someString" : "Hello", and then "other" :

558
00:27:36,555 --> 00:27:40,156
<whatever SomeOtherType looks like in JSON> looks like would

559
00:27:40,225 --> 00:27:44,194
be embedded in there, you see? And so it can be recursively

560
00:27:44,263 --> 00:27:48,965
going down. Now we might not want the JSON

561
00:27:49,034 --> 00:27:52,702
to look exactly like this, so can we tune this? Yeah we can,

562
00:27:52,771 --> 00:27:57,007
look at this. In JSON, for example, the keys usually

563
00:27:57,075 --> 00:28:00,443
don't have camel case, you know like some capital D data

564
00:28:00,512 --> 00:28:03,513
like we do for our variables. Usually the keys are,

565
00:28:03,582 --> 00:28:07,183
the words are separate with underbar like "som_date". So

566
00:28:07,252 --> 00:28:10,787
we can easily change the keys that are generated when we use

567
00:28:10,856 --> 00:28:15,158
that JSON coder by adding a private enum called CodingKeys

568
00:28:15,227 --> 00:28:17,327
which is a string-type enum. And

569
00:28:17,396 --> 00:28:19,830
it has to implement a protocol coding key. And

570
00:28:19,899 --> 00:28:22,799
all it does is has a case, it's an enum, right?

571
00:28:22,868 --> 00:28:25,168
Has a case for every var that we want encoded.

572
00:28:25,237 --> 00:28:26,870
So if we have a var we don't want encoded,

573
00:28:26,939 --> 00:28:28,672
just don't put that case there. And

574
00:28:28,741 --> 00:28:30,340
if you have a var that you do want encoded, but

575
00:28:30,409 --> 00:28:33,510
you want it to change the key, just say equals the key you

576
00:28:33,578 --> 00:28:36,946
want. So here I've said case someDate = "som_date", so

577
00:28:37,015 --> 00:28:40,550
now in the JSON it's gonna say som_date equals, instead of

578
00:28:40,619 --> 00:28:43,687
someDate. And notice I didn't put someString case in there

579
00:28:43,756 --> 00:28:46,490
at all, so someString is not even gonna be put in the JSON.

580
00:28:48,427 --> 00:28:50,894
So this is a really cool, simple way to

581
00:28:50,963 --> 00:28:55,065
customize the JSON that you generate from your type. Now,

582
00:28:55,134 --> 00:28:57,400
I'm not even gonna really talk about this, but

583
00:28:57,469 --> 00:29:01,537
you can implement init from decoder. The thing that

584
00:29:01,606 --> 00:29:05,641
actually pulls the thing out of the jJSON. If you want

585
00:29:05,710 --> 00:29:08,411
to do some validation or some kind of complicated thing, or

586
00:29:08,480 --> 00:29:12,282
if for example you have a type that swift can't encode.

587
00:29:12,351 --> 00:29:15,418
Some new type that you invented that's not made up of

588
00:29:15,487 --> 00:29:18,188
other types that swift can encode and you wanna do it,

589
00:29:18,257 --> 00:29:20,490
you can do it. I just put this here as kind of,

590
00:29:20,558 --> 00:29:23,426
so you can look at it later to see how you do it.

591
00:29:23,495 --> 00:29:25,561
There's a container in the decoder and you get it and

592
00:29:25,630 --> 00:29:28,431
it's got keys and values that looks like a dictionary. It's

593
00:29:28,500 --> 00:29:32,402
not that hard. One thing is when you're decoding a class,

594
00:29:32,471 --> 00:29:34,838
you have to be here for the call supe_init, right?

595
00:29:34,907 --> 00:29:37,073
Cuz you're decoding, you have to implement init.

596
00:29:37,142 --> 00:29:39,575
So you gotta call supe_init. But don't call supe_init

597
00:29:39,644 --> 00:29:42,546
with the same decoder that was sent to you. Decoder was sent

598
00:29:42,614 --> 00:29:46,283
to you is for decoding your vars. You want to send this

599
00:29:46,351 --> 00:29:49,153
thing from the container called superDecoder.

600
00:29:49,221 --> 00:29:52,889
As the decoder of your superclasses bars. And

601
00:29:52,958 --> 00:29:56,860
then of course, you could also implement encoding to encode

602
00:29:56,929 --> 00:29:59,496
random types that aren't part of the swifting.

603
00:29:59,564 --> 00:30:00,864
Again, I'm not gonna go over this.

604
00:30:00,933 --> 00:30:01,832
You won't have to do any of this for

605
00:30:01,900 --> 00:30:04,734
your homework of course. But for your final project

606
00:30:04,803 --> 00:30:07,571
at least you know this can be done, is to implement encode

607
00:30:07,639 --> 00:30:11,040
and init for yourself. All right, so that's it for

608
00:30:11,109 --> 00:30:14,177
archiving. Archiving, the whole point is we take some

609
00:30:14,246 --> 00:30:17,413
object graphed of swift stuff and we turn it into a data.

610
00:30:17,482 --> 00:30:18,915
And the data is either gonna be JSON or

611
00:30:18,984 --> 00:30:21,217
property list format. So we have a data,

612
00:30:21,286 --> 00:30:24,487
now we wanna store that data in the file system.

613
00:30:24,556 --> 00:30:25,588
We're gonna put it in a file.

614
00:30:25,657 --> 00:30:29,426
It's just a normal file. Remember that iOS is Unix. And

615
00:30:29,495 --> 00:30:32,929
so we have a unix filesystem underneath of course and

616
00:30:32,998 --> 00:30:36,500
starts at slash any other of the unix file system and

617
00:30:36,568 --> 00:30:39,502
all we need to do to store our data blog is just write it

618
00:30:39,571 --> 00:30:43,740
to a file. So how do we access this unix file system in iOS?

619
00:30:43,809 --> 00:30:45,909
Well, the most important thing to

620
00:30:45,977 --> 00:30:48,712
understand is that the only part of Unix file system you

621
00:30:48,780 --> 00:30:53,116
can access is your sand box. Your sandbox is this little

622
00:30:53,184 --> 00:30:55,418
enclosed space. It's the only place you can write.

623
00:30:55,487 --> 00:30:57,887
You can't write into any system files anywhere.

624
00:30:57,956 --> 00:30:59,889
You can't write into any other app's information.

625
00:30:59,958 --> 00:31:02,692
You can only write in your sandbox. Why does iOS

626
00:31:02,761 --> 00:31:07,731
restrict you to a sandbox. Well, three main reasons.

627
00:31:07,799 --> 00:31:12,636
One, Security. Because we want to make sure that no other

628
00:31:12,704 --> 00:31:16,473
app can come along and break your app somehow, make it so

629
00:31:16,542 --> 00:31:19,810
that your app doesn't work. Privacy,

630
00:31:19,878 --> 00:31:21,845
you're collecting user information, whatever,

631
00:31:21,914 --> 00:31:24,080
you don't want other malicious apps to be looking in there

632
00:31:24,149 --> 00:31:26,983
and getting that information. And an underrated one is

633
00:31:27,052 --> 00:31:30,954
cleanup. You wanna be able to clean up when the user says,

634
00:31:31,022 --> 00:31:34,090
I don't want this app anymore. If you have everything in

635
00:31:34,159 --> 00:31:36,426
a sandbox, you can delete that sandbox, and now everything

636
00:31:36,494 --> 00:31:39,595
that app has ever done is gone. So, there's the clean-up

637
00:31:39,664 --> 00:31:43,666
part of it. So, Access in the Unix file system is all about

638
00:31:43,735 --> 00:31:47,103
finding a starting point in this sandbox. And there's

639
00:31:47,172 --> 00:31:49,939
a few starting points that you can find. For example,

640
00:31:50,008 --> 00:31:52,675
there is your application directory in the sandbox.

641
00:31:52,744 --> 00:31:56,179
This has your executable, all your storyboards, JPEG files,

642
00:31:56,248 --> 00:31:58,148
your image assets, all those things.

643
00:31:58,216 --> 00:32:02,486
This part of your sandbox, you can get a Unix path to it.

644
00:32:02,554 --> 00:32:04,654
But it's completely not writeable.

645
00:32:04,723 --> 00:32:07,323
You cannot write to any of this. You can only read it.

646
00:32:07,392 --> 00:32:09,125
If there was something you needed to write in there,

647
00:32:09,194 --> 00:32:12,229
like let's say you pass some initial database or something,

648
00:32:12,297 --> 00:32:13,463
you would have to copy it out into

649
00:32:13,531 --> 00:32:15,866
one of the other places in your sandbox, and

650
00:32:15,934 --> 00:32:19,069
edit it from there. Another place in your sandbox,

651
00:32:19,138 --> 00:32:21,771
really important, is the Documents directory.

652
00:32:21,840 --> 00:32:25,041
This is where you store stuff that the user perceives

653
00:32:25,110 --> 00:32:27,177
as their data in document form.

654
00:32:27,245 --> 00:32:30,146
And the reason it's important that it be user-perceived

655
00:32:30,215 --> 00:32:33,083
as a document is because this directory, what's in there,

656
00:32:33,152 --> 00:32:36,253
is gonna be visible in the files app in iOS 11.

657
00:32:36,321 --> 00:32:39,756
I don't know if you all have seen iOS 11, played with it

658
00:32:39,825 --> 00:32:42,559
much. There's a new app in there, Files, and it shows

659
00:32:42,627 --> 00:32:45,362
you all the files in all the Document directories of all

660
00:32:45,430 --> 00:32:48,598
the apps. So don't put things in the Documents directory

661
00:32:48,666 --> 00:32:52,502
unless they're perceived as documents by the user.

662
00:32:52,570 --> 00:32:54,704
There's also applications support. That's where you can

663
00:32:54,773 --> 00:32:58,174
put the stuff that the user creates that's not a document,

664
00:32:58,243 --> 00:33:00,610
because that's not gonna show up in Files. And

665
00:33:00,679 --> 00:33:01,911
then there's other directories,

666
00:33:01,980 --> 00:33:03,914
about a dozen other ones. One of them, for example,

667
00:33:03,982 --> 00:33:06,183
is Caches directory. That's where you can put temporary

668
00:33:06,251 --> 00:33:09,052
stuff that can be deleted at any other time, at any time,

669
00:33:09,121 --> 00:33:12,022
and recreated. For example, in your homework for this week,

670
00:33:12,090 --> 00:33:14,190
I'm gonna ask you to take your image galleries and

671
00:33:14,259 --> 00:33:18,161
cache those images. So that when people drag stuff in and

672
00:33:18,229 --> 00:33:19,262
then they start scrolling around,

673
00:33:19,331 --> 00:33:20,463
instead of constantly going back and

674
00:33:20,531 --> 00:33:21,798
fetching those things all the time,

675
00:33:21,867 --> 00:33:23,299
you cache them in the file system. Well,

676
00:33:23,368 --> 00:33:26,035
you're gonna wanna put that in the Caches directory because

677
00:33:26,104 --> 00:33:28,905
it won't count against your app in terms of disk space

678
00:33:28,973 --> 00:33:31,541
usage, and you can always just re-fetch it again if you,

679
00:33:31,610 --> 00:33:35,312
if the cache gets blown away.

680
00:33:35,380 --> 00:33:37,313
All right, so, you need to get paths to all these things.

681
00:33:37,382 --> 00:33:40,450
So how do you get a path to these special directories, and

682
00:33:40,518 --> 00:33:44,220
then start building on it to build your own paths.

683
00:33:44,289 --> 00:33:46,622
Well the first thing to understand is that all

684
00:33:46,691 --> 00:33:48,591
the access to the file system is gonna happen through

685
00:33:48,660 --> 00:33:51,695
two classes, or two, two objects. They're not classes,

686
00:33:51,764 --> 00:33:54,230
they're struct. But one is FileManager,

687
00:33:54,299 --> 00:33:57,466
and the other one is URL. And you've already learned about

688
00:33:57,535 --> 00:34:01,137
URL because we've used URLs to the network resources,

689
00:34:01,205 --> 00:34:03,840
HTTP resources, and things like that. Well, you can also

690
00:34:03,908 --> 00:34:06,742
have URLs to local resources, things on your disk.

691
00:34:06,811 --> 00:34:09,078
And our URL is essentially just a path,

692
00:34:09,147 --> 00:34:13,216
a Unix path to the file. So the,

693
00:34:13,284 --> 00:34:16,552
what you're gonna do before you do anything is find one

694
00:34:16,621 --> 00:34:19,556
of these sandbox directories, cuz you cannot only write and

695
00:34:19,625 --> 00:34:21,524
read from those sandbox directories. So

696
00:34:21,593 --> 00:34:26,362
there's really two methods to get a sandbox URL, and

697
00:34:26,431 --> 00:34:28,498
I'm going to show you one of them here, which is, I kind of

698
00:34:28,567 --> 00:34:31,701
prefer. I'll actually show the other one maybe in the demo.

699
00:34:31,769 --> 00:34:35,605
It's a FileManager method, and the FileManager is kind of

700
00:34:35,674 --> 00:34:38,274
like user default in that we use a shared one called

701
00:34:38,343 --> 00:34:40,977
default. Although sometimes we would actually wanna

702
00:34:41,046 --> 00:34:43,713
create a different FileManager by saying FileManager

703
00:34:43,782 --> 00:34:45,515
open parentheses closed parentheses, right? Just

704
00:34:45,584 --> 00:34:47,583
calling its initializer, which takes no argument, and I'll

705
00:34:47,652 --> 00:34:50,786
talk about when we'd wanna do that a little bit later here.

706
00:34:50,855 --> 00:34:54,524
So this one is called URL for directory in DomainMask,

707
00:34:54,592 --> 00:34:59,162
appropriate for create. So let's look at these arguments.

708
00:34:59,231 --> 00:35:02,331
The for directory is the sandbox directory you want.

709
00:35:02,400 --> 00:35:05,067
Like the documentDirectory, the cachesDirectory,

710
00:35:05,136 --> 00:35:06,970
the applicationSupportDirectory.

711
00:35:07,038 --> 00:35:08,671
That's there and

712
00:35:08,740 --> 00:35:12,242
it's specified via an enum here. And

713
00:35:12,310 --> 00:35:14,110
I show you some examples of what they are at the bottom.

714
00:35:14,179 --> 00:35:16,879
You can obviously go look it up in the documentation,

715
00:35:16,948 --> 00:35:19,749
what's available there. In domainMask, is always

716
00:35:19,818 --> 00:35:23,185
.userDomainMask on iOS because we have the sandbox, and

717
00:35:23,254 --> 00:35:25,155
we can only look in the sandbox.

718
00:35:25,223 --> 00:35:28,992
On MacOS it could be a shared network domain.

719
00:35:29,060 --> 00:35:31,327
It could be the systems shared domain center, but

720
00:35:31,396 --> 00:35:34,263
on iOS it's always userDomainMask right there.

721
00:35:34,332 --> 00:35:37,266
Appropriate for just, you're always gonna set that to nil.

722
00:35:37,335 --> 00:35:39,502
That's basically if you're gonna replace a file,

723
00:35:39,571 --> 00:35:41,905
you want to specify the URL of what you're gonna replace so

724
00:35:41,973 --> 00:35:44,840
you can make sure it's on the same volume as the,

725
00:35:44,909 --> 00:35:48,545
the URL you are getting. Again, kind of not meaningful

726
00:35:48,613 --> 00:35:51,213
in iOS most of the time, so that's usually just nil. And

727
00:35:51,282 --> 00:35:52,616
then create is an important one.

728
00:35:52,684 --> 00:35:55,251
That says whether you're gonna create that sandbox,

729
00:35:55,320 --> 00:35:56,386
special sandbox directory,

730
00:35:56,455 --> 00:35:59,055
cuz not all of them exist when your app is created.

731
00:35:59,123 --> 00:36:01,424
Like applicationSupport does not exist, so you'll have to

732
00:36:01,493 --> 00:36:03,459
make sure you say create: true, right there. Doesn't

733
00:36:03,528 --> 00:36:05,428
hurt to say create: true, I think documentDirectory

734
00:36:05,496 --> 00:36:08,397
actually is already created for you, but, can't hurt. So

735
00:36:08,466 --> 00:36:12,068
this is how you get a URL, you see the return value is a URL,

736
00:36:12,136 --> 00:36:14,738
into the sandbox. Now that you have a URL in the sandbox,

737
00:36:14,806 --> 00:36:17,607
now you can start writing files. And the way you do that

738
00:36:17,675 --> 00:36:21,478
is by using the URL method appendingPathComponent.

739
00:36:21,547 --> 00:36:24,213
So adds a directory or the name of a file

740
00:36:24,282 --> 00:36:27,217
onto the end of that URL, you can even add file extensions.

741
00:36:27,285 --> 00:36:28,317
It's perfectly legal, by the way,

742
00:36:28,386 --> 00:36:32,689
to say appendingPathComponent food.jpg, you don't have to

743
00:36:32,757 --> 00:36:34,357
do the extension with a separate call there.

744
00:36:34,426 --> 00:36:37,460
But anyway, you're gonna use that to build a URL that

745
00:36:37,529 --> 00:36:40,663
extends past the sandbox, and it can have directories and

746
00:36:40,731 --> 00:36:43,833
stuff. You can, once you have URL,

747
00:36:43,901 --> 00:36:47,069
you can find out about things like, is it a FileURL, or

748
00:36:47,138 --> 00:36:50,806
is it an HTTP URL? You can get things like the right date.

749
00:36:50,875 --> 00:36:54,144
Is this a directory? How big is this file?

750
00:36:54,213 --> 00:36:57,714
From this method, resourceValues in URL.

751
00:36:57,782 --> 00:37:00,683
And resourceValues for keys takes a bunch of keys, like

752
00:37:00,752 --> 00:37:03,385
file size and stuff like that, and goes and looks it up in

753
00:37:03,454 --> 00:37:06,555
the file system and returns a dictionary with those keys and

754
00:37:06,624 --> 00:37:09,391
the value it found. That's why the value is Any right there.

755
00:37:09,460 --> 00:37:13,363
It could be a number, it could be a string, things like that.

756
00:37:13,431 --> 00:37:15,799
So you can find out a lot about your files there.

757
00:37:17,235 --> 00:37:18,835
How do you read and write files?

758
00:37:18,904 --> 00:37:21,738
We do that with data. And you've already seen this,

759
00:37:21,806 --> 00:37:26,075
actually. We used data to read a file off the internet,

760
00:37:26,144 --> 00:37:29,078
with an HTTP URL. Of course you can do that with a FileURL

761
00:37:29,147 --> 00:37:32,582
as well. We did not use the options when we did it,

762
00:37:32,651 --> 00:37:34,083
because we used the default options,

763
00:37:34,152 --> 00:37:36,753
which you mostly will. But there are some read options

764
00:37:36,822 --> 00:37:38,921
you can go look at. And to write files,

765
00:37:38,990 --> 00:37:41,724
you're going to send this to data, write(to url.

766
00:37:41,792 --> 00:37:45,061
And it also has options you can look at as well. So that

767
00:37:45,129 --> 00:37:48,197
is how we read and and write to the file system. We have

768
00:37:48,266 --> 00:37:51,401
a data, probably one we got by archiving the thing to JSON or

769
00:37:51,469 --> 00:37:54,137
whatever with their archiver, and we just read and

770
00:37:54,206 --> 00:37:57,606
write with these two methods from the file system. So

771
00:37:57,675 --> 00:37:59,909
you can see it's all about just getting the right URL,

772
00:37:59,978 --> 00:38:00,877
and then it's easy to read and

773
00:38:00,946 --> 00:38:04,213
write. I want to talk a little bit more about

774
00:38:04,282 --> 00:38:07,484
FileManager. You can do a lot of other things besides just

775
00:38:07,552 --> 00:38:09,385
give you a URL of something in the sandbox.

776
00:38:09,454 --> 00:38:12,355
For example, it can tell you whether a file exists, on,

777
00:38:12,423 --> 00:38:15,658
in the file system. It can move files, copy files,

778
00:38:15,726 --> 00:38:19,028
create directories, enumerate directories, delete files,

779
00:38:19,097 --> 00:38:20,897
all that stuff, all in FileManager.

780
00:38:20,966 --> 00:38:23,433
FileManager has probably a hundred methods in it for

781
00:38:23,502 --> 00:38:26,936
doing all that. FileManager also has a delegate. And

782
00:38:27,005 --> 00:38:30,206
that delegate, almost all of the methods are, should this.

783
00:38:30,275 --> 00:38:33,142
Should I allow opening this file? Should I allow you

784
00:38:33,211 --> 00:38:35,044
to move this file. They're kind of should things, so

785
00:38:35,113 --> 00:38:37,546
a delegate can control whether the FileManager is allowed to

786
00:38:37,615 --> 00:38:41,917
do things. That and the fact that FileManager is thread

787
00:38:41,986 --> 00:38:45,254
safe, but only within one instance of the FileManager.

788
00:38:45,323 --> 00:38:47,757
So if you have a FileManager on another thread besides

789
00:38:47,826 --> 00:38:49,592
the main thread, it's thread safe but

790
00:38:49,661 --> 00:38:52,862
only if that FileManager was created on that thread.

791
00:38:52,931 --> 00:38:55,731
And the filemanager.default that I showed you before,

792
00:38:55,800 --> 00:38:57,967
that's the main thread one. So you don't want to use

793
00:38:58,036 --> 00:39:00,470
filemanager.default in any of the thread, but the main

794
00:39:00,538 --> 00:39:04,006
thread. And of course, if you're gonna set a delegate on

795
00:39:04,075 --> 00:39:06,175
the FileManager, you probably don't want to set the delegate

796
00:39:06,244 --> 00:39:09,178
of filemanager.default. That's kind of a shared FileManager

797
00:39:09,247 --> 00:39:11,948
everybody's using in the main thread. So

798
00:39:12,016 --> 00:39:15,384
you probably want to create a FileManager in that case.

799
00:39:15,453 --> 00:39:18,421
Multiple FileManagers know how to not step on each others'

800
00:39:18,490 --> 00:39:22,758
toes. All right? So we've learned the simple little

801
00:39:22,827 --> 00:39:25,929
database, which was the user default thing

802
00:39:25,997 --> 00:39:28,197
where we could store property lists for, that's just for

803
00:39:28,266 --> 00:39:31,767
settings and stuff like that. Then we learned about how to

804
00:39:31,836 --> 00:39:34,570
do archiving, much more powerful. We can store other

805
00:39:34,639 --> 00:39:37,006
things and Swift will mostly just do the code for us,

806
00:39:37,075 --> 00:39:40,843
but sometimes we can get involved if we want. And

807
00:39:40,912 --> 00:39:44,080
it generates datas, then we learn how to take those datas,

808
00:39:44,148 --> 00:39:46,782
with JSON or whatever in them, and store them in the file

809
00:39:46,851 --> 00:39:49,852
system, using FileManager and URL. Now I'm gonna talk about

810
00:39:49,921 --> 00:39:53,022
the next persistence thing which is core data. So

811
00:39:53,091 --> 00:39:54,290
core data is if you have

812
00:39:54,359 --> 00:39:57,159
a large amount of data and you need to search over it.

813
00:39:57,228 --> 00:39:59,228
In other words, you need a database.

814
00:39:59,297 --> 00:40:03,566
So core data is essentially a SQL database. With an objected

815
00:40:03,635 --> 00:40:06,902
oriented API. So you interact with this database.

816
00:40:06,971 --> 00:40:10,272
It looks like Swift objects, but behind the scene those

817
00:40:10,341 --> 00:40:13,343
Swift objects are actually in a database, a SQL database.

818
00:40:13,411 --> 00:40:14,811
Now Core Data is very powerful and

819
00:40:14,879 --> 00:40:17,480
can actually have back ends that are different than SQL,

820
00:40:17,549 --> 00:40:21,951
but for the most part we use SQL back end for Core Data. So

821
00:40:22,020 --> 00:40:24,987
that's what Core Data is, it's very efficient,

822
00:40:25,056 --> 00:40:27,189
beautifully object oriented.

823
00:40:27,258 --> 00:40:28,358
Now, I cannot,

824
00:40:28,426 --> 00:40:30,593
I don't have time in this quarter to talk about it, but

825
00:40:30,662 --> 00:40:33,796
luckily, I spent a whole week on it last quarter. So

826
00:40:33,865 --> 00:40:37,032
you can go and look on iTunes U and see two lectures on it,

827
00:40:37,101 --> 00:40:38,267
it hasn't really changed that much for

828
00:40:38,336 --> 00:40:41,103
iOS 11, so it'll all be good. This is a great

829
00:40:41,172 --> 00:40:43,739
not covered in lecture feature for your final project,

830
00:40:43,808 --> 00:40:46,042
because I'm not really gonna cover it in this lecture.

831
00:40:46,111 --> 00:40:47,943
I'm gonna kinda give you an overview of it. But

832
00:40:48,012 --> 00:40:48,944
you can easily go back and

833
00:40:49,013 --> 00:40:50,446
watch my last lecture and, boom,

834
00:40:50,515 --> 00:40:52,548
learn all about it and be ready to go. So

835
00:40:52,617 --> 00:40:55,251
all I'm gonna do here is a brief overview of it.

836
00:40:55,320 --> 00:40:56,886
If you want a detailed of Core Data, and

837
00:40:56,954 --> 00:40:59,522
it is a great feature to do for your final project,

838
00:40:59,591 --> 00:41:03,493
believe me. Go check that iTunes U. All right,

839
00:41:03,561 --> 00:41:07,263
so it's a way of having this object-oriented programming

840
00:41:07,331 --> 00:41:11,266
layer with the back end SQL. How do we do that, how do we

841
00:41:11,335 --> 00:41:14,770
match those two things up? Well we actually have a tool

842
00:41:14,839 --> 00:41:18,207
in Xcode which is a visual mapper. You build all your

843
00:41:18,276 --> 00:41:21,611
objects and all their vars essentially in this mapper.

844
00:41:21,680 --> 00:41:23,946
And the mapper is used to figure out how to do that

845
00:41:24,015 --> 00:41:27,783
mapping forward for you, and it just happens automatically.

846
00:41:27,852 --> 00:41:30,252
So if any of you who know about databases, databases

847
00:41:30,321 --> 00:41:33,890
have tables. They have rows in the tables that are records,

848
00:41:33,959 --> 00:41:36,059
they have columns which are the fields.

849
00:41:36,127 --> 00:41:38,061
That's still happening behind the scenes, but

850
00:41:38,129 --> 00:41:40,263
you don't see any of that when you're programming,

851
00:41:40,331 --> 00:41:42,331
because you're using an object-oriented API.

852
00:41:42,400 --> 00:41:45,401
So this is what the Visual Mapper looks like, right,

853
00:41:45,470 --> 00:41:48,738
it's in Xcode here. And here I have a couple objects here,

854
00:41:48,807 --> 00:41:50,773
a tweet and a twitter user.

855
00:41:50,842 --> 00:41:53,042
And those are going to map to objects in my code and

856
00:41:53,111 --> 00:41:55,811
tables in the database. And then we've got the fields like

857
00:41:55,880 --> 00:41:57,380
the tweet's got a created date,

858
00:41:57,448 --> 00:42:01,017
a unique identifier of the tweet, the text of the tweet.

859
00:42:01,085 --> 00:42:03,819
And its even got a var which is the tweeter which points

860
00:42:03,888 --> 00:42:06,723
over to the twitter user and on the twitter user side,

861
00:42:06,791 --> 00:42:10,059
it's got a var called tweets. Which is gonna point back,

862
00:42:10,127 --> 00:42:14,229
which is actually a set of tweet objects. So

863
00:42:14,298 --> 00:42:17,332
this mapping is being used by Core Data on both sides.

864
00:42:17,401 --> 00:42:18,467
On the object side to make

865
00:42:18,536 --> 00:42:20,002
all of these things look like objects, and

866
00:42:20,071 --> 00:42:21,537
on the other side to build the tables and

867
00:42:21,606 --> 00:42:25,775
rows in the database. So let's at how we, what it kind

868
00:42:25,844 --> 00:42:27,943
of looks like to do this in code so you get an idea.

869
00:42:28,012 --> 00:42:30,112
Again, I'm not trying to teach you how to do Core Data here.

870
00:42:30,181 --> 00:42:32,581
This is to kind of give you an idea of what it looks like.

871
00:42:32,650 --> 00:42:34,684
The most important thing about core data to understand,

872
00:42:34,753 --> 00:42:37,219
is that we access all of it from a code using

873
00:42:37,288 --> 00:42:41,190
an NSManagedObjectContext. So this context is key and

874
00:42:41,259 --> 00:42:43,693
there's two ways to get this context. One,

875
00:42:43,762 --> 00:42:45,261
you know how when we created our project?

876
00:42:45,330 --> 00:42:46,662
There was that little switch there, that said,

877
00:42:46,731 --> 00:42:49,899
use core data, you remember that? So you can flip that on

878
00:42:49,968 --> 00:42:53,335
and then you'll get a method in your app delegate, which we

879
00:42:53,404 --> 00:42:55,304
haven't talked about. We'll talk about that next week,

880
00:42:55,373 --> 00:42:57,340
that is giving you the context.

881
00:42:57,409 --> 00:42:59,041
It's actually a var that gives you the context.

882
00:42:59,110 --> 00:43:02,078
So that's one way, another way is to create a subclass,

883
00:43:02,146 --> 00:43:04,947
it's use a subclass of UIDocument, which I'm gonna

884
00:43:05,015 --> 00:43:09,385
talk about later today. Which will give you the context,

885
00:43:09,453 --> 00:43:12,488
and UIDocument is a way of abstracting a document.

886
00:43:12,556 --> 00:43:14,523
So that's a way of looking at your entire database,

887
00:43:14,592 --> 00:43:18,527
as just like one big document. It could be a huge document

888
00:43:18,596 --> 00:43:21,230
cuz those databases can be big. But

889
00:43:21,299 --> 00:43:23,099
those are the two ways to get a context.

890
00:43:23,167 --> 00:43:25,768
Once you have a two, a context in your hand,

891
00:43:25,836 --> 00:43:28,604
now you can start doing all this access in the database

892
00:43:28,672 --> 00:43:30,940
looking like an object. And here's what this looks like.

893
00:43:31,008 --> 00:43:35,344
So here, for example, I'm creating a tweet. And the only

894
00:43:35,412 --> 00:43:38,314
argument to the initializer there is the context,

895
00:43:38,382 --> 00:43:40,817
which tells, is basically the database to put it in. But

896
00:43:40,885 --> 00:43:42,785
then if I want to set the text of the tweet,

897
00:43:42,854 --> 00:43:45,221
I just say tweet.text, it looks just like Swift,

898
00:43:45,289 --> 00:43:49,058
tweet.created equals a date. Yeah I can even create Joe,

899
00:43:49,126 --> 00:43:51,927
a twitter user in the same context as the tweet and

900
00:43:51,996 --> 00:43:56,899
say tweet.tweeter = Joe. I can even go tweet.tweeter.name =

901
00:43:56,967 --> 00:44:00,702
"Joe Schmo" in other words use Swift notation to go

902
00:44:00,771 --> 00:44:03,672
through objects that I'm linked to. So

903
00:44:03,741 --> 00:44:08,377
it really looks just exactly like Swift. And I can also

904
00:44:08,446 --> 00:44:12,181
delete objects by just asking the context to delete them.

905
00:44:12,250 --> 00:44:15,050
Changes that I made are actually autosaved if

906
00:44:15,119 --> 00:44:18,587
I use that UIDocument approach to getting the context.

907
00:44:18,656 --> 00:44:21,357
But if I used the Use Core Data switch to do it,

908
00:44:21,425 --> 00:44:24,360
then I have to save it. The only thing about the save is

909
00:44:24,428 --> 00:44:25,994
it can throw. As you can imagine,

910
00:44:26,063 --> 00:44:28,364
if I'm saving this stuff out to the SQL database,

911
00:44:28,433 --> 00:44:30,966
I could get SQL errors or some kind of file system full or

912
00:44:31,035 --> 00:44:34,203
things like that. So I have to catch the errors, if I'm not

913
00:44:34,271 --> 00:44:37,907
gonna do the UIDocument based auto-saving. Now how about

914
00:44:37,976 --> 00:44:41,143
searching for objects, tweets and twitter users in there.

915
00:44:41,212 --> 00:44:42,912
So here I'm gonna search for

916
00:44:42,981 --> 00:44:47,050
some twitter users that have tweeted in the last 24 hours.

917
00:44:47,118 --> 00:44:49,418
So first, I asked the TwitterUser class for

918
00:44:49,487 --> 00:44:51,987
a fetch request. You see the first line there where I'm

919
00:44:52,056 --> 00:44:54,089
saying TwitterUser.fetchRequest?

920
00:44:54,158 --> 00:44:57,093
Then this fetch request, I set a predicate on it, see,

921
00:44:57,162 --> 00:44:59,962
NSPredicate format? And predicate is a way of

922
00:45:00,031 --> 00:45:04,299
specifying the search you want in text. It's not quite like

923
00:45:04,368 --> 00:45:08,971
SQL, but it's very English oriented. So here I want any

924
00:45:09,040 --> 00:45:13,809
tweets that were created after 24 hours ago. Okay

925
00:45:13,877 --> 00:45:16,478
cuz yesterday is a var I made on the previous line which

926
00:45:16,547 --> 00:45:21,350
is timeIntervalSinceNow minus 24 hours. So

927
00:45:21,418 --> 00:45:22,651
I've described my search that way.

928
00:45:22,720 --> 00:45:26,755
I also can describe how I want the result sorted. Here I'm

929
00:45:26,824 --> 00:45:30,225
gonna sort them by the name of the TwitterUser. And

930
00:45:30,294 --> 00:45:33,796
then I just asked the context please go fetch those things

931
00:45:33,864 --> 00:45:37,533
that match that. And it gives me back an array of those

932
00:45:37,602 --> 00:45:40,402
things, as we might expect. And if none, if nothing

933
00:45:40,471 --> 00:45:43,739
matches then I'll get an empty array. If there was an error,

934
00:45:43,807 --> 00:45:46,775
like maybe my predicate had a syntax error I said,

935
00:45:46,844 --> 00:45:50,646
like any twoots got created by, then this is gonna throw.

936
00:45:50,715 --> 00:45:53,282
And I'll have to catch it and figure that out.

937
00:45:53,350 --> 00:45:55,651
But otherwise it returns in array of objects.

938
00:45:55,720 --> 00:45:58,220
So it's really easy to query the database too, and it's

939
00:45:58,289 --> 00:46:00,823
using SQL to do that search so it's super efficient.

940
00:46:00,891 --> 00:46:04,794
And it's, even large values coming back, it's efficient

941
00:46:04,862 --> 00:46:07,363
about that as well. I can't talk about how it does that,

942
00:46:07,432 --> 00:46:10,032
but it's also very efficient even if huge things are,

943
00:46:10,101 --> 00:46:13,803
are returned. And Core Data can do so much more.

944
00:46:13,872 --> 00:46:15,338
It has great support for multithreading,

945
00:46:15,406 --> 00:46:17,773
it has a very close integration with UITableView,

946
00:46:17,842 --> 00:46:18,641
as you can imagine.

947
00:46:18,710 --> 00:46:21,010
You, you know, often might want the information from

948
00:46:21,079 --> 00:46:23,812
the database to appear in a table. You can even set it up

949
00:46:23,881 --> 00:46:27,016
so a table is always showing the result of a fetch request,

950
00:46:27,084 --> 00:46:29,151
even if the database changes from underneath.

951
00:46:29,219 --> 00:46:31,621
It just automatically updates the table, and auto,

952
00:46:31,689 --> 00:46:33,656
you don£t have to do anything in your code.

953
00:46:33,725 --> 00:46:36,358
Just say what fetch request you want associated with

954
00:46:36,427 --> 00:46:39,128
the table. It does lots of good databasey,

955
00:46:39,196 --> 00:46:42,799
things like optimistic locking and rolling back changes.

956
00:46:42,867 --> 00:46:46,468
You can do undo redo really easily with this,

957
00:46:46,537 --> 00:46:49,905
with the Core Data. And so I,

958
00:46:49,973 --> 00:46:51,874
I can't cover any of that, but I just wanted to give you

959
00:46:51,943 --> 00:46:53,709
a kind of an idea of what Core Data can do,

960
00:46:53,778 --> 00:46:56,645
cuz it's a very powerful framework in iOS. So check out

961
00:46:56,713 --> 00:47:00,316
my last quarter's iTunes U to figure out how to do that.

962
00:47:00,385 --> 00:47:03,452
I do a full demo the whole deal. All right, so

963
00:47:03,521 --> 00:47:06,688
next topic is also something I can't talk about this week.

964
00:47:06,757 --> 00:47:10,559
But I also did a week on this the quarter before that.

965
00:47:10,628 --> 00:47:12,361
So if you go back one more iTunes U,

966
00:47:12,429 --> 00:47:14,997
instead of Core Data that quarter I did Cloud Kit,

967
00:47:15,065 --> 00:47:17,866
and instead of either of them this quarter we'£e doing

968
00:47:17,935 --> 00:47:19,602
the document browser. So

969
00:47:19,670 --> 00:47:22,137
every quarter I like to spend a week on persistence, and

970
00:47:22,206 --> 00:47:25,374
I kind of do a different thing each quarter. This quarter I'm

971
00:47:25,443 --> 00:47:29,344
doing document, two quarters ago I did Cloud Kit. So

972
00:47:29,413 --> 00:47:32,548
what is Cloud Kit? Cloud Kit is a database also,

973
00:47:32,617 --> 00:47:35,384
in the same way that Core Data is, but it's not a SQL

974
00:47:35,452 --> 00:47:38,253
database. It's a very simple database, it just has

975
00:47:38,322 --> 00:47:40,823
kind of objects and the properties in those objects.

976
00:47:40,892 --> 00:47:43,592
And you can query on them, but they're simple queries. And

977
00:47:43,660 --> 00:47:46,963
relationships between things have to be pretty simple and

978
00:47:47,031 --> 00:47:50,165
straightforward. But what's incredible about it is,

979
00:47:50,234 --> 00:47:53,135
it's on the network. So this is a network database, so

980
00:47:53,204 --> 00:47:56,238
Core Data, you can have your database file on the network.

981
00:47:56,306 --> 00:47:59,007
But when you start accessing it, it has to bring the file

982
00:47:59,076 --> 00:48:01,476
down to your local machine Cuz it's a local SQL.

983
00:48:01,545 --> 00:48:04,046
Database thing whereas Cloud Kit

984
00:48:04,115 --> 00:48:06,315
actually when you make a request to search for

985
00:48:06,384 --> 00:48:09,351
something, it does it over the Internet to iCloud and

986
00:48:09,419 --> 00:48:12,822
says search that database and send the results back. So

987
00:48:12,890 --> 00:48:17,326
Cloud Kit's API is completely asynchronous, right,

988
00:48:17,395 --> 00:48:19,528
you make requests and then you provide a closure, and

989
00:48:19,597 --> 00:48:22,531
it calls you back later when it's got the result. So

990
00:48:22,600 --> 00:48:25,167
this requires a certain thoughtfulness

991
00:48:25,236 --> 00:48:27,769
in programming when things can take a long

992
00:48:27,838 --> 00:48:30,472
time like that, okay. You've already seen this a little bit

993
00:48:30,541 --> 00:48:33,475
with multi-threading in your homework, hopefully, but

994
00:48:33,544 --> 00:48:36,578
it's kinda amplified in Cloud Kit. Now it's not,

995
00:48:36,647 --> 00:48:39,180
it's not bad, it just requires you to think in a certain way

996
00:48:39,249 --> 00:48:41,383
as you're programming. So

997
00:48:41,452 --> 00:48:42,985
the important components of Cloud Kit,

998
00:48:43,053 --> 00:48:45,454
you got record types, that's kind of like classes.

999
00:48:45,523 --> 00:48:48,357
You've got fields, that's like a var in class,

1000
00:48:48,426 --> 00:48:51,560
record, that's an instance of a class. A reference, that's

1001
00:48:51,629 --> 00:48:55,197
like a pointer to another class, you got databases and

1002
00:48:55,266 --> 00:48:58,033
zones inside databases. You've got containers that contain

1003
00:48:58,102 --> 00:49:01,503
databases. You've got queries, that's like a fetch request,

1004
00:49:01,572 --> 00:49:04,373
a little bit in Core Data. It's actually quite similar

1005
00:49:04,442 --> 00:49:05,774
to a fetch request in Core Data. And

1006
00:49:05,843 --> 00:49:09,244
then you've got subscriptions which are a fantastic feature.

1007
00:49:09,313 --> 00:49:12,747
That's, you make a query, and you give it to the server, and

1008
00:49:12,816 --> 00:49:14,984
you say anytime the database changes,

1009
00:49:15,052 --> 00:49:17,019
such that this query would change,

1010
00:49:17,088 --> 00:49:20,222
send me a push notification. Do you all know what a push...

1011
00:49:20,291 --> 00:49:23,592
who knows what a push notification is? So

1012
00:49:23,661 --> 00:49:27,162
not everyone, but most people. So a push notification is just

1013
00:49:27,231 --> 00:49:29,899
something that comes to your app, and it'll even wake

1014
00:49:29,967 --> 00:49:33,002
your app up and say, whoa, some information has arrived.

1015
00:49:33,070 --> 00:49:35,071
And that is one of the coolest, if not the coolest,

1016
00:49:35,139 --> 00:49:37,672
feature in Cloud Kit, is that you'll get notified

1017
00:49:37,741 --> 00:49:39,909
when the database changes in a way that you care about.

1018
00:49:39,977 --> 00:49:42,978
Those are called subscriptions. But

1019
00:49:43,046 --> 00:49:44,646
you're gonna see, I'm gonna show you some code for

1020
00:49:44,715 --> 00:49:47,749
Cloud Kit. It's not like Core Data in that it doesn't look

1021
00:49:47,818 --> 00:49:49,301
like Swift in the code. You've got more function calls and

1022
00:49:49,302 --> 00:49:50,785
as much just

1023
00:49:50,854 --> 00:49:54,223
stuff. Now to use Cloud Kit, you have to turn on iCloud.

1024
00:49:54,292 --> 00:49:56,591
And you do this, like a lot of things you have to turn on,

1025
00:49:56,660 --> 00:49:58,660
like push notifications and other things,

1026
00:49:58,729 --> 00:50:01,797
in the Capabilities section of your project settings.

1027
00:50:01,865 --> 00:50:03,832
So you're gonna go there to Capabilities, and

1028
00:50:03,901 --> 00:50:07,569
you're gonna flip this switch for iCloud ON. And

1029
00:50:07,638 --> 00:50:10,338
then you're gonna turn on this little Cloud Kit switch down

1030
00:50:10,407 --> 00:50:12,808
here, and that's gonna enable that capability for

1031
00:50:12,877 --> 00:50:14,977
you to use Cloud Kit. If you don't turn this on,

1032
00:50:15,045 --> 00:50:17,212
you won't be able to use it. And when you do that,

1033
00:50:17,281 --> 00:50:19,848
there's gonna be this little button down at the bottom

1034
00:50:19,917 --> 00:50:22,651
called Cloud Kit Dashboard. This Cloud Kit Dashboard,

1035
00:50:22,720 --> 00:50:25,253
let's press it and see what it looks like.

1036
00:50:25,322 --> 00:50:27,489
It's gonna go to this place on the Web, where it's gonna show

1037
00:50:27,558 --> 00:50:30,726
you your database schema. So all your record types,

1038
00:50:30,795 --> 00:50:33,061
and all the little fields in it, not just that, but

1039
00:50:33,130 --> 00:50:36,565
the actual data. Which it's not that useful once you ship

1040
00:50:36,634 --> 00:50:38,767
your app because you're gonna have thousands of users

1041
00:50:38,835 --> 00:50:40,869
generating so much data you can't even look at it.

1042
00:50:40,938 --> 00:50:43,005
But in development, it's really great,

1043
00:50:43,074 --> 00:50:45,708
because you create a object and you can go look at it and

1044
00:50:45,776 --> 00:50:48,410
make sure it got in there and it's got the right data or

1045
00:50:48,479 --> 00:50:53,014
whatever. So this dashboard is how you kind of work on your

1046
00:50:53,083 --> 00:50:57,519
schema. It's not quite like the Core Data schema

1047
00:50:57,588 --> 00:51:02,057
editor thing. Because in Cloud Kit, different than Core Data,

1048
00:51:02,126 --> 00:51:03,859
it builds the schema as you go.

1049
00:51:03,927 --> 00:51:07,729
As soon as you, if you say create an object of this name,

1050
00:51:07,798 --> 00:51:11,433
it'll just go create it. It's, it's gonna do it on the fly,

1051
00:51:11,502 --> 00:51:14,269
you don't have to go and pre-build your schema like you

1052
00:51:14,338 --> 00:51:17,473
do in Core Data. That's what this is talking about, dynamic

1053
00:51:17,541 --> 00:51:19,842
schema creation. And this only works during development,

1054
00:51:19,911 --> 00:51:22,277
obviously. Once you ship it to your users, then

1055
00:51:22,346 --> 00:51:26,548
it's not gonna create classes and fields on the fly as you

1056
00:51:26,616 --> 00:51:28,717
access them. But you're in development, it's really nice,

1057
00:51:28,786 --> 00:51:31,353
it's really easy, to just start writing code, and have

1058
00:51:31,422 --> 00:51:34,990
it start building the database that would match that code.

1059
00:51:35,059 --> 00:51:36,725
All right, so here's what the code looks like. You're

1060
00:51:36,794 --> 00:51:39,594
gonna see it doesn't look like as nice as Core Data.

1061
00:51:39,663 --> 00:51:42,330
So you have to get a database, so usually,

1062
00:51:42,399 --> 00:51:45,267
you're gonna use the public or private cloud database.

1063
00:51:45,336 --> 00:51:48,737
Then to create a tweet, you see you're gonna say CKRecord,

1064
00:51:48,805 --> 00:51:51,907
CK is Cloud Kit. CKRecord with the name Tweet which would

1065
00:51:51,975 --> 00:51:55,077
automatically add that table to the database if it didn't

1066
00:51:55,146 --> 00:51:58,180
exist. Then you're gonna say tweet subquote

1067
00:51:58,249 --> 00:52:01,750
text = the text. And then to have a tweeter you have to say

1068
00:52:01,819 --> 00:52:05,520
CKRecord TwitterUser. And then say tweet sub tweeter =

1069
00:52:05,589 --> 00:52:10,058
CKReference to record tweeter with the action delete this

1070
00:52:10,127 --> 00:52:12,861
thing if the thing it's in gets deleted. So you see,

1071
00:52:12,930 --> 00:52:14,530
it's more verbose and not,

1072
00:52:14,598 --> 00:52:18,233
doesn't look like Swift, to be doing all this stuff. And

1073
00:52:18,302 --> 00:52:20,802
of course things like saving are asynchronous, right.

1074
00:52:20,871 --> 00:52:22,938
So here I wanna save this tweet in the database.

1075
00:52:23,007 --> 00:52:25,874
Well, it's going to, I have to provide this closure,

1076
00:52:25,943 --> 00:52:28,477
and it's gonna call me back once it's finished or

1077
00:52:28,545 --> 00:52:32,480
if there were an error. Now this networking programming,

1078
00:52:32,549 --> 00:52:35,350
always a lot of error handling. And so

1079
00:52:35,419 --> 00:52:37,753
if you guys haven't done networking programming,

1080
00:52:37,822 --> 00:52:40,455
get used to it, there are 29 different errors in Cloud Kit

1081
00:52:40,524 --> 00:52:44,459
error. And not all of them can happen on every operation, but

1082
00:52:44,528 --> 00:52:47,796
a lot of them can. For example, I've shown the error

1083
00:52:47,865 --> 00:52:50,598
here NotAuthenticated. Because since it's Cloud Kit,

1084
00:52:50,667 --> 00:52:53,068
if the user's not logged in to iCloud on their device,

1085
00:52:53,136 --> 00:52:55,070
then it's not going to know who they are, so

1086
00:52:55,139 --> 00:52:57,406
it's not gonna work. So you could get that error.

1087
00:52:57,475 --> 00:53:00,842
You can get network timeouts, all kinds of stuff. So

1088
00:53:00,911 --> 00:53:04,246
that's just a different way of program, you have to kind of

1089
00:53:04,315 --> 00:53:07,349
get used to it, this asynchronous programming.

1090
00:53:07,418 --> 00:53:10,385
Here's what a query looks like. This is the analog of

1091
00:53:10,454 --> 00:53:14,089
the fetch request. You still use NSPredicate. So

1092
00:53:14,158 --> 00:53:17,259
like text contains some searchString or

1093
00:53:17,328 --> 00:53:21,329
whatever. But the predicates can't be quite as complicated

1094
00:53:21,398 --> 00:53:24,399
as in Core Data. They have to be fairly straightforward

1095
00:53:24,468 --> 00:53:26,635
predicates. But then you create a CKQuery,

1096
00:53:26,704 --> 00:53:29,137
which is a Cloud Kit query, and then you say perform, and

1097
00:53:29,206 --> 00:53:32,173
of course it's asynchronous. So you provide a closure, and

1098
00:53:32,242 --> 00:53:35,511
it calls you back with the results of doing that query.

1099
00:53:35,579 --> 00:53:38,180
So that's what querying, querying looks like.

1100
00:53:38,249 --> 00:53:41,717
Again, pretty simple, but asynchronous and

1101
00:53:41,785 --> 00:53:45,353
not as powerful as Core Data. Standing queries or

1102
00:53:45,422 --> 00:53:48,356
subscriptions, I can't really show you what that code looks

1103
00:53:48,425 --> 00:53:51,526
like because I haven't taught you push notifications.

1104
00:53:51,595 --> 00:53:53,895
Push notifications are not that difficult.

1105
00:53:53,964 --> 00:53:57,599
There's a whole framework for it called UserNotifications.

1106
00:53:57,668 --> 00:53:59,668
But it doesn't make sense for me to show you what it

1107
00:53:59,737 --> 00:54:01,804
looks like when I haven't taught you that.

1108
00:54:01,872 --> 00:54:04,806
So we'll put that off til later. Maybe I'll try and show

1109
00:54:04,875 --> 00:54:08,543
an example of a Cloud Kit, push notification happening,

1110
00:54:08,612 --> 00:54:13,248
when we cover that. All right, now, next topic.

1111
00:54:13,316 --> 00:54:16,885
So this is the topic that I am gonna spend this week on,

1112
00:54:16,954 --> 00:54:19,555
which is document-based apps. So

1113
00:54:19,623 --> 00:54:23,325
this is persistence when the thing that you're persisting

1114
00:54:23,394 --> 00:54:26,561
is perceived by the user as a document.

1115
00:54:26,630 --> 00:54:30,532
For example, emoji art. I create a beautiful emoji art

1116
00:54:30,601 --> 00:54:34,903
document, put my ghost and my bike in there, my bees.

1117
00:54:34,972 --> 00:54:37,972
And then I wanted to save like a document, and then the user

1118
00:54:38,041 --> 00:54:41,042
is gonna go create a different one with some other image and

1119
00:54:41,111 --> 00:54:42,477
some other stuff in there.

1120
00:54:42,546 --> 00:54:44,045
And they wanna save that as a different document.

1121
00:54:44,114 --> 00:54:45,914
So they, you see how they viewed them as documents.

1122
00:54:45,982 --> 00:54:47,849
Same thing with your image gallery homework.

1123
00:54:47,918 --> 00:54:49,751
You have a gallery of images that you built, and

1124
00:54:49,819 --> 00:54:52,287
then maybe you wanna have a different gallery of images

1125
00:54:52,356 --> 00:54:52,954
that are related in

1126
00:54:53,023 --> 00:54:56,191
some other way. Those are perceived as documents. So

1127
00:54:56,260 --> 00:55:00,728
we're gonna talk about a mechanism that iOS API has for

1128
00:55:00,797 --> 00:55:04,632
storing things of document that is fantastic. It takes

1129
00:55:04,701 --> 00:55:07,903
care of absolutely everything you wanna do with a document,

1130
00:55:07,971 --> 00:55:08,703
and you have to hard,

1131
00:55:08,772 --> 00:55:12,841
do hardly any work to make it work. All you have to do is

1132
00:55:12,909 --> 00:55:16,177
actually convert your model into a data and back.

1133
00:55:16,246 --> 00:55:20,381
And that's it, and it manages absolutely everything else. So

1134
00:55:20,450 --> 00:55:22,050
when I say it manages everything else,

1135
00:55:22,118 --> 00:55:26,754
what do I mean? Well, opening, writing, reading, closing

1136
00:55:26,823 --> 00:55:31,126
document files asynchronously is all handled by UIDocument.

1137
00:55:31,195 --> 00:55:36,297
Now why do I want my documents opened, say, asynchronously?

1138
00:55:36,366 --> 00:55:39,534
Why do I care? My documents aren't big, it's not gonna

1139
00:55:39,603 --> 00:55:41,269
take that much time to write them to the file system,

1140
00:55:41,338 --> 00:55:45,840
who cares? Well, UIDocument supports saving your files in

1141
00:55:45,909 --> 00:55:51,646
iCloud drive. On the network, and that could be slower. So,

1142
00:55:51,715 --> 00:55:54,415
if you had to write the code to save them to iCloud drive,

1143
00:55:54,484 --> 00:55:57,185
you'd be very sad indeed, because you'd have to do all

1144
00:55:57,254 --> 00:56:00,054
that networking code to figure out how did I get this thing

1145
00:56:00,123 --> 00:56:02,523
over the network? Did it fail? Is it the network?

1146
00:56:02,592 --> 00:56:04,292
Whereas, this way you use UIDocument,

1147
00:56:04,361 --> 00:56:07,495
you just say save. It'll just call you back when it's done.

1148
00:56:07,564 --> 00:56:09,465
It's all asynchronous, it's awesome.

1149
00:56:11,034 --> 00:56:14,135
It also will auto save your document. And, again,

1150
00:56:14,204 --> 00:56:16,871
I told you one of the ways to get a context for your core

1151
00:56:16,940 --> 00:56:19,841
data is to create a UI managed documents, it's called,

1152
00:56:19,910 --> 00:56:23,044
which is a subclass UIDocument for core data databases, and

1153
00:56:23,113 --> 00:56:25,547
it will autosave it. Well the same thing happened for yours.

1154
00:56:25,616 --> 00:56:27,682
Your documents can just be automatically saved,

1155
00:56:27,751 --> 00:56:29,651
you don't even have to save them. And

1156
00:56:29,720 --> 00:56:32,487
the most important thing about UIDocument is that

1157
00:56:32,556 --> 00:56:36,391
it integrates with iOS 11's Files app, and

1158
00:56:36,460 --> 00:56:38,059
the document browser. And we're gonna see,

1159
00:56:38,128 --> 00:56:41,029
if we get to it today, which hopefully we will,

1160
00:56:41,098 --> 00:56:44,666
what that means cuz it means a lot, it's very powerful. So

1161
00:56:44,735 --> 00:56:47,969
what do you need to do to make UIDocument work?

1162
00:56:48,038 --> 00:56:51,240
You want to have UIDocument. Well I'm gonna assume you

1163
00:56:51,308 --> 00:56:54,275
already have an MVC that displays your document and

1164
00:56:54,344 --> 00:56:57,546
that it has some var or vars that are its model, right.

1165
00:56:57,615 --> 00:56:59,447
This is MVC, of course it's got a model.

1166
00:56:59,516 --> 00:57:02,483
So like in emoji art we don't have our model yet

1167
00:57:02,552 --> 00:57:05,887
in emoji art, but imagine I had some var of type emoji

1168
00:57:05,956 --> 00:57:09,524
art, which was the model for what I'm showing. It would

1169
00:57:09,593 --> 00:57:12,427
have the URL of the image, and it would have all the emoji,

1170
00:57:12,495 --> 00:57:15,163
and where they were, and the size they were, right?

1171
00:57:15,232 --> 00:57:17,032
That would be the model of the thing.

1172
00:57:17,100 --> 00:57:20,201
So I'm gonna assume I start there. So all you need to do

1173
00:57:20,270 --> 00:57:23,572
to turn your app into working with UIDocument is to be able

1174
00:57:23,640 --> 00:57:28,176
to convert that model to a data, and convert from a data

1175
00:57:28,245 --> 00:57:30,312
back to the model. Well, earlier in this lecture,

1176
00:57:30,380 --> 00:57:32,447
didn't I just show you exactly how to do that with

1177
00:57:32,516 --> 00:57:36,017
the archiver? Really easy. So you could use JSON format

1178
00:57:36,086 --> 00:57:38,654
as the file format of your document, and

1179
00:57:38,722 --> 00:57:42,023
just use the archiving to turn your model back and forth

1180
00:57:42,092 --> 00:57:44,859
between the data, and that's really all you have to do.

1181
00:57:44,928 --> 00:57:47,095
The only other thing you might wanna do Is

1182
00:57:47,163 --> 00:57:49,998
tell the UIDocument whenever your document changes,

1183
00:57:50,067 --> 00:57:52,568
like if you drag a new emoji in or whatever, and

1184
00:57:52,636 --> 00:57:54,903
then it'll autosave. Cuz you have to tell it that,

1185
00:57:54,972 --> 00:57:56,871
otherwise it doesn't know when to autosave.

1186
00:57:56,940 --> 00:57:59,207
But that is literally called one function,

1187
00:57:59,275 --> 00:58:03,010
my document changed, and it'll figure it out from there.

1188
00:58:03,079 --> 00:58:05,213
That's it, that's all you have to do to make UIDocument work.

1189
00:58:05,282 --> 00:58:09,317
Really implement two methods, get and set my model as

1190
00:58:09,385 --> 00:58:14,489
a data. So how do we do that? We subclass UIDocument and

1191
00:58:14,558 --> 00:58:17,592
we override two methods, the one that creates the data and

1192
00:58:17,661 --> 00:58:21,229
one gets our model from the data. Now we're almost always

1193
00:58:21,298 --> 00:58:25,133
going to want to add a var in our UIDocument subclass,

1194
00:58:25,202 --> 00:58:28,469
which is the model. The model that we're going to be

1195
00:58:28,538 --> 00:58:30,372
the converting to and from a data. So,

1196
00:58:30,440 --> 00:58:32,307
here if I had an EmojiArtDocument

1197
00:58:32,376 --> 00:58:35,676
subclassing UIdocument, I'm adding a var called EmojiArt,

1198
00:58:35,745 --> 00:58:36,812
which is of type EmojiArt.

1199
00:58:36,880 --> 00:58:40,115
That's presumably the type of the model that

1200
00:58:40,184 --> 00:58:44,453
I have in my EmojiArtDocument. Now there are other methods

1201
00:58:44,521 --> 00:58:46,721
you can override in UIDocument that do some things.

1202
00:58:46,790 --> 00:58:48,857
I'll even talk about one of them towards the end. But

1203
00:58:48,926 --> 00:58:52,427
the main two things you wanna do is the reading and

1204
00:58:52,495 --> 00:58:54,729
writing of the data. And the only thing you have to do to

1205
00:58:54,798 --> 00:58:59,401
create the UIDocument is specify the URL it's at.

1206
00:58:59,470 --> 00:59:03,305
So the only initializer that exists for

1207
00:59:03,373 --> 00:59:05,473
UIDocument, it takes one argument,

1208
00:59:05,542 --> 00:59:08,776
as you can see it in yellow right there, fileURL, and

1209
00:59:08,845 --> 00:59:12,146
that is gonna be the URL of the document. Now I'm

1210
00:59:12,215 --> 00:59:15,583
gonna show you later that this URL might be given to you and

1211
00:59:15,652 --> 00:59:19,921
might be an iCloud drive, and you might not even care.

1212
00:59:19,990 --> 00:59:23,424
But you also could, of course, create a URL somewhere

1213
00:59:23,493 --> 00:59:26,494
presumably in the documents directory of your sandbox, and

1214
00:59:26,563 --> 00:59:30,832
create your own document if you want. But actually, in iOS

1215
00:59:30,901 --> 00:59:35,603
11, usually we let the files app mechanism give us the URL.

1216
00:59:35,672 --> 00:59:37,806
The user goes to where they want the file to be, and

1217
00:59:37,874 --> 00:59:40,141
they say create document, and it gives us URL, and

1218
00:59:40,210 --> 00:59:42,244
we just call this to create our UIDocument.

1219
00:59:43,847 --> 00:59:46,014
Now once we've created our UIDocument,

1220
00:59:46,083 --> 00:59:48,783
we're gonna set that var that I defined at the top of

1221
00:59:48,852 --> 00:59:51,653
the screen there. We're gonna set that model in there and

1222
00:59:51,721 --> 00:59:53,554
then UIDocument's gonna take it from there.

1223
00:59:53,623 --> 00:59:54,889
It's gonna read and write the file and

1224
00:59:54,958 --> 00:59:57,992
everything. All right, so how about doing this conversion

1225
00:59:58,061 --> 01:00:01,830
from emojiArt to data and from data to emojiArt. So

1226
01:00:01,899 --> 01:00:04,599
here's the two methods. This is the one that converts your

1227
01:00:04,668 --> 01:00:08,570
model into a data, it's called contents for type, okay.

1228
01:00:08,639 --> 01:00:10,839
It does throw, You could throw. If you have a problem

1229
01:00:10,907 --> 01:00:13,507
converting your emojiArt to a Data, you could throw. And

1230
01:00:13,576 --> 01:00:17,212
I'll show you where that thing gets thrown to. And notice it

1231
01:00:17,280 --> 01:00:20,215
returns an Any. You would think that would return a Data

1232
01:00:20,284 --> 01:00:22,450
right there, but it returns an Any because you can actually

1233
01:00:22,519 --> 01:00:26,754
also represent your document as a directory full of files.

1234
01:00:26,823 --> 01:00:29,257
That's called a FileWrapper. But

1235
01:00:29,326 --> 01:00:32,160
we're just gonna talk about the Data way of doing it.

1236
01:00:32,229 --> 01:00:33,762
If you wanna do the FileWrapper way, you'll have

1237
01:00:33,831 --> 01:00:35,730
to look up the documentation for file wrappers.

1238
01:00:35,799 --> 01:00:37,532
It's not that hard, but it's a little more

1239
01:00:37,601 --> 01:00:40,368
complicated than just turning it into a Data blob. And

1240
01:00:40,437 --> 01:00:42,738
so how am I gonna implement this method?

1241
01:00:42,806 --> 01:00:44,739
Real easy, I'm gonna use that archiving stuff, and

1242
01:00:44,808 --> 01:00:47,241
use a JSON encoder or something right here, and

1243
01:00:47,310 --> 01:00:50,411
create a Data object. And I just return it, that's it.

1244
01:00:50,480 --> 01:00:53,748
So this often is a one liner, this contents for type. Now

1245
01:00:53,817 --> 01:00:56,985
that type that you see right there, yeah I already said you

1246
01:00:57,053 --> 01:00:59,387
could throw there. So the type that's passed along there,

1247
01:00:59,456 --> 01:01:03,658
that's a UTI, a universal type identifier. And

1248
01:01:03,727 --> 01:01:05,493
I'm gonna talk a little bit about what that is

1249
01:01:05,562 --> 01:01:09,464
in a few slides. This is not a type like .jpeg.

1250
01:01:09,532 --> 01:01:12,434
This is a type like public.json, which would

1251
01:01:12,502 --> 01:01:16,538
be a JSON file, or public.img, it's an image file. That's

1252
01:01:16,607 --> 01:01:18,573
the kind of thing that's gonna be in that type name.

1253
01:01:18,642 --> 01:01:21,509
Usually you don't care because usually your UIDocument only

1254
01:01:21,578 --> 01:01:25,013
opens one kind of file anyway, like an emojiArt document, so

1255
01:01:25,082 --> 01:01:27,215
you don't even care what that type is. But you might

1256
01:01:27,284 --> 01:01:30,118
be a UIDocument that can be in different formats and then

1257
01:01:30,186 --> 01:01:33,755
maybe you care. Alright, how about the other way around?

1258
01:01:33,824 --> 01:01:35,890
You've got a data, that's handed to you,

1259
01:01:35,959 --> 01:01:37,792
you gotta turn into your model.

1260
01:01:37,861 --> 01:01:42,229
Again you're probably going to use that JSON Decoder, and

1261
01:01:42,298 --> 01:01:47,001
take the data and turn it back into an emoji art. And again,

1262
01:01:47,070 --> 01:01:50,738
it's got the types there, load from contents of type, that's

1263
01:01:50,807 --> 01:01:54,041
UTI. This one throws as well. This one you're more likely to

1264
01:01:54,110 --> 01:01:57,579
throw, because here you're being given a JSON thing or

1265
01:01:57,647 --> 01:02:00,749
a Data blob, and you're turning into EmojiArt. It

1266
01:02:00,817 --> 01:02:03,385
might be corrupted, it might not be in the right format,

1267
01:02:03,453 --> 01:02:07,021
something's wrong with it, so you might throw here.

1268
01:02:07,090 --> 01:02:09,758
And, in fact, that's all you need to do is implement those

1269
01:02:09,826 --> 01:02:12,294
two methods. And now you can use all the methods in

1270
01:02:12,362 --> 01:02:15,863
UIDocument like open, which opens your documents.

1271
01:02:15,932 --> 01:02:19,501
And it's asynchronous, so you provide it a closure there,

1272
01:02:19,569 --> 01:02:21,536
and it even tells you whether you successfully did it or

1273
01:02:21,605 --> 01:02:24,205
not. If it doesn't successfully open it, you're

1274
01:02:24,273 --> 01:02:26,241
gonna be looking at this thing called documentState, and

1275
01:02:26,309 --> 01:02:28,676
I'm gonna talk about that in a second, all right.

1276
01:02:28,745 --> 01:02:30,611
So that's how you open a document. And you do have to

1277
01:02:30,680 --> 01:02:33,447
open your UIDocument before you can use it, of course,

1278
01:02:33,516 --> 01:02:35,349
because UIDocument wants to go and get the file,

1279
01:02:35,418 --> 01:02:36,851
and get the data, and stuff like that.

1280
01:02:36,920 --> 01:02:40,055
Call the method that converts it into an emoji art or

1281
01:02:40,123 --> 01:02:43,358
whatever, but you do have to open your file.

1282
01:02:43,427 --> 01:02:46,627
You can save your file explicitly or you can just do

1283
01:02:46,696 --> 01:02:49,264
auto saving. If you do auto saving, this is the method you

1284
01:02:49,332 --> 01:02:52,968
have to call to tell your UIDocument I've changed.

1285
01:02:53,036 --> 01:02:57,571
UpdateChangeCount(.done). Another way, by the way, to do

1286
01:02:57,640 --> 01:03:01,709
this is to use the undoManager of UIDocument. Unfortunately,

1287
01:03:01,778 --> 01:03:04,112
I don't have time to teach you about doing undo.

1288
01:03:04,181 --> 01:03:05,180
undoManager is a really

1289
01:03:05,248 --> 01:03:08,049
cool little class where every time you do an operation,

1290
01:03:08,118 --> 01:03:09,784
like drag a new emoji in or

1291
01:03:09,853 --> 01:03:12,186
resize it, you go to the undoManager and

1292
01:03:12,255 --> 01:03:15,056
say, I just did this operation and here's a closure for

1293
01:03:15,125 --> 01:03:20,127
how to undo it. And then, it automatically does Undo/Redo,

1294
01:03:20,196 --> 01:03:22,464
and just pulls those closures out so you can undo and

1295
01:03:22,532 --> 01:03:25,299
then redo, go back and forth. And of course, if you use

1296
01:03:25,368 --> 01:03:28,670
the UIDocument's undoManager to do that, then it will know

1297
01:03:28,738 --> 01:03:31,739
that the document has changed when you do these Undo and

1298
01:03:31,808 --> 01:03:37,045
Redo things. So that's another way to use the undoManager.

1299
01:03:37,114 --> 01:03:39,780
If you wanna explicitly save, there is a save.

1300
01:03:39,849 --> 01:03:42,383
The save one is not like open, it actually has a couple

1301
01:03:42,452 --> 01:03:46,755
arguments here. The reason you have save to URL is for

1302
01:03:46,823 --> 01:03:50,291
save as. Because of course a document knows its own URL,

1303
01:03:50,360 --> 01:03:52,527
that was specified in its initialize, or

1304
01:03:52,595 --> 01:03:56,464
the file URL. So save to URL allows you to save it off to

1305
01:03:56,532 --> 01:03:59,100
another URL like save as. And then that for

1306
01:03:59,169 --> 01:04:01,703
document save operation, unfortunately when you save,

1307
01:04:01,772 --> 01:04:04,272
you have to know whether this is the initial document

1308
01:04:04,341 --> 01:04:07,274
creation save Or whether it's a subsequent safe.

1309
01:04:07,343 --> 01:04:09,010
You have to tell the system that.

1310
01:04:09,079 --> 01:04:11,612
I'm not sure why it makes you do that versus it going out

1311
01:04:11,681 --> 01:04:14,382
and figuring it out, I think it's just for flexibility.

1312
01:04:14,451 --> 01:04:17,585
Cuz it can save into so many different kinds of containers.

1313
01:04:17,654 --> 01:04:21,055
iCloud drive, your local file system, it can even save into

1314
01:04:21,124 --> 01:04:25,126
things like Box. So maybe some of them don't allow it to ask

1315
01:04:25,194 --> 01:04:28,630
the question of whether the file exists or not, I'm not

1316
01:04:28,698 --> 01:04:31,899
exactly sure why it does that. But when you say it,

1317
01:04:31,968 --> 01:04:35,636
you do have to know whether you're creating it or not.

1318
01:04:35,705 --> 01:04:37,404
When you're done with your document,

1319
01:04:37,473 --> 01:04:40,408
you're gonna want to close it. Of course, the big thing this

1320
01:04:40,477 --> 01:04:43,545
does is save it, if it's got any outstanding changes.

1321
01:04:43,613 --> 01:04:46,381
And again, if it fails closing it, you're gonna have this

1322
01:04:46,450 --> 01:04:48,950
document state thing. So what is, what I keep saying,

1323
01:04:49,019 --> 01:04:50,852
look at the document state if things fail,

1324
01:04:50,921 --> 01:04:53,822
what is that about? Well, let's look at the document

1325
01:04:53,890 --> 01:04:56,324
state, the document state is a var in UIDocument.

1326
01:04:56,393 --> 01:04:58,827
You can look at it and see how your document's doing.

1327
01:04:58,895 --> 01:05:01,829
Here's some of the values, normal, that means your

1328
01:05:01,898 --> 01:05:05,166
document is ready to use. Just do whatever you want with it,

1329
01:05:05,234 --> 01:05:07,601
that's the normal state. There's also closed,

1330
01:05:07,670 --> 01:05:10,838
that means either you haven't opened it or you tried to open

1331
01:05:10,907 --> 01:05:13,808
it and it failed, and it's still in the closed state.

1332
01:05:13,877 --> 01:05:18,279
There's savingError, which is you tried to save it and

1333
01:05:18,348 --> 01:05:22,183
it failed. There's also editingDisabled, and that is

1334
01:05:22,251 --> 01:05:25,586
a method on UIDocument, which is disable editing.

1335
01:05:25,655 --> 01:05:28,023
And why would you ever want to disable editing? Well, for

1336
01:05:28,091 --> 01:05:30,958
example, the core data document, UIManagedDocument.

1337
01:05:31,027 --> 01:05:33,962
It disables editing when it's doing some sort of

1338
01:05:34,031 --> 01:05:36,865
a SQL operation to update the database. Now it

1339
01:05:36,933 --> 01:05:40,068
only happens for a microsecond that it's disabled.

1340
01:05:40,136 --> 01:05:43,071
But essentially when you set editingDisabled as the state

1341
01:05:43,139 --> 01:05:46,040
of your document. You just would not want to allow users

1342
01:05:46,109 --> 01:05:48,342
to drag new emoji in, or resize anything.

1343
01:05:48,411 --> 01:05:50,945
Not really an issue in something like emoji art,

1344
01:05:51,014 --> 01:05:53,981
where it's very simple. But it can be an issue in the core

1345
01:05:54,050 --> 01:05:57,518
data, or some other more complicated storage mechanism.

1346
01:05:57,587 --> 01:05:59,620
Then there's the progressAvailable state.

1347
01:05:59,689 --> 01:06:02,223
That means you did open on a document, and

1348
01:06:02,292 --> 01:06:06,027
the document is huge, and it's downloading it from iCloud or

1349
01:06:06,096 --> 01:06:09,163
something. And this will tell you that progress,

1350
01:06:09,232 --> 01:06:11,666
it will be the progress bar in the UIDocument,

1351
01:06:11,734 --> 01:06:13,434
will tell you how far along it is.

1352
01:06:13,503 --> 01:06:16,604
And it will stay in this state until it's fully downloaded,

1353
01:06:16,673 --> 01:06:21,409
and then it will move to open, or normal rather. And finally,

1354
01:06:21,478 --> 01:06:24,345
there's inConflict, which is a very fascinating one.

1355
01:06:24,413 --> 01:06:27,915
Since the document can be stored in a network container,

1356
01:06:27,984 --> 01:06:31,352
it might get saved somewhere that had network access at

1357
01:06:31,421 --> 01:06:34,255
the time. And then start editing in another place that

1358
01:06:34,324 --> 01:06:37,325
didn't have network access, or vice versa. Resulting in two

1359
01:06:37,393 --> 01:06:40,694
versions of the app finally getting saved up to iCloud.

1360
01:06:40,763 --> 01:06:43,931
And now you have two versions that might be conflicting, and

1361
01:06:44,000 --> 01:06:45,299
that's what this is about.

1362
01:06:45,368 --> 01:06:48,536
Now, you're not gonna deal with this in your app.

1363
01:06:48,605 --> 01:06:51,039
You're probably gonna take the default behavior, which is,

1364
01:06:51,108 --> 01:06:53,140
it uses the one with the most recent file date.

1365
01:06:53,209 --> 01:06:56,544
Whichever one was written most recently, it uses. But

1366
01:06:56,613 --> 01:06:59,113
if you want to resolve the difference, and you want to

1367
01:06:59,182 --> 01:07:01,950
notice this and resolve it, you can use this NSFileVersion

1368
01:07:02,018 --> 01:07:05,052
static method here. And get all the different versions,

1369
01:07:05,121 --> 01:07:07,088
and look at the differences of them.

1370
01:07:07,157 --> 01:07:09,524
And maybe offer the user some choices, whatever,

1371
01:07:09,592 --> 01:07:12,260
that'd be up to you. But for things like emoji art,

1372
01:07:12,328 --> 01:07:15,396
you're probably fine with just always taking the latest

1373
01:07:15,465 --> 01:07:17,932
version, whichever one was saved latest.

1374
01:07:19,869 --> 01:07:23,304
DocumentState as var can also be observed in the same way

1375
01:07:23,372 --> 01:07:26,674
that the keyboard observing can happen. Remember, I told

1376
01:07:26,742 --> 01:07:28,943
you that there was a way you could like tell the system,

1377
01:07:29,012 --> 01:07:31,512
hey, if the keyboard comes up, tell me about it, right?

1378
01:07:31,581 --> 01:07:34,315
That's called a notification, same thing here. You can say,

1379
01:07:34,384 --> 01:07:36,650
hey, if my document state changes, tell me about it,

1380
01:07:36,719 --> 01:07:39,220
and it would tell you that. I'm going to tell you how

1381
01:07:39,289 --> 01:07:42,223
to do this next week when we talk about notifications,

1382
01:07:42,292 --> 01:07:45,727
and I'll mention document state and keyboard. And show

1383
01:07:45,795 --> 01:07:51,232
you what a code looks like to watch your document state.

1384
01:07:51,301 --> 01:07:54,802
Finally I'm gonna talk about a cool little extra method you

1385
01:07:54,871 --> 01:07:57,672
can override in UIDocument to put a thumbnail image.

1386
01:07:57,740 --> 01:08:01,742
Instead of your documents icon. By default,

1387
01:08:01,811 --> 01:08:04,244
when you look at your documents in the files app or

1388
01:08:04,313 --> 01:08:07,749
whatever, they'll have icons, right? Whatever the file type

1389
01:08:07,817 --> 01:08:10,518
icon, the jpg file icon, whatever that is. Or

1390
01:08:10,587 --> 01:08:13,821
if you have an emoji art type of file, which we are gonna

1391
01:08:13,889 --> 01:08:18,059
talk about, on Wednesday, it would show that icon.

1392
01:08:18,127 --> 01:08:19,494
But you can also say,

1393
01:08:19,563 --> 01:08:22,563
when the user sees my file in the file system,

1394
01:08:22,632 --> 01:08:26,601
actually use this thumbnail image of it as its icon.

1395
01:08:26,670 --> 01:08:29,003
This is a really powerful way to make it easier for

1396
01:08:29,072 --> 01:08:31,305
users to find which document they want.

1397
01:08:31,374 --> 01:08:34,108
Because imagine emoji art, you do some nice art, and

1398
01:08:34,177 --> 01:08:37,278
it makes a little thumbnail of it. So you can actually see

1399
01:08:37,347 --> 01:08:39,947
the document before you open it in the file system,

1400
01:08:40,016 --> 01:08:42,883
it's like the icon of the document. And to do that,

1401
01:08:42,952 --> 01:08:46,287
all you have to do is override this UIDocument method,

1402
01:08:46,356 --> 01:08:48,856
called File Attributes to Write to URL for

1403
01:08:48,925 --> 01:08:52,660
Operation. This is normally just going to return

1404
01:08:52,729 --> 01:08:56,531
a dictionary of the file attributes like, is this file

1405
01:08:56,599 --> 01:08:59,634
hidden? Things like that, but you can override it,

1406
01:08:59,702 --> 01:09:02,803
get the super file attributes it would normally return.

1407
01:09:02,872 --> 01:09:06,507
And then add this very special dictionary item called

1408
01:09:06,576 --> 01:09:10,778
URLResourceKey.thumbnailDicti- onaryKey. And the value of it

1409
01:09:10,846 --> 01:09:14,415
actually is another dictionary. With the key being

1410
01:09:14,484 --> 01:09:19,620
ThumbnailDictionaryItem.NSThu- mbnail1024x1024SizeKey. And

1411
01:09:19,689 --> 01:09:24,759
the value is a UIImage. So you add this to the dictionary,

1412
01:09:24,828 --> 01:09:27,929
if you have a UIImage to be the thumbnail, and return it.

1413
01:09:27,997 --> 01:09:31,766
Now, it says there NSThumbnail1024x1024, but

1414
01:09:31,835 --> 01:09:34,402
it actually can be any size.

1415
01:09:34,471 --> 01:09:37,105
It seems to me that if the size gets too small,

1416
01:09:37,173 --> 01:09:40,040
then it will start using the icon for the file. So

1417
01:09:40,109 --> 01:09:43,411
it can't be too small, and I'm not sure what too small is,

1418
01:09:43,479 --> 01:09:46,513
probably has something to do with how big the icon image

1419
01:09:46,582 --> 01:09:49,050
is. Maybe if it gets smaller than the icon image,

1420
01:09:49,119 --> 01:09:50,718
I'm really not sure how it chooses.

1421
01:09:50,787 --> 01:09:53,654
But, as long as the image is decent sized,

1422
01:09:53,723 --> 01:09:56,323
and I don't know if there's a limit too

1423
01:09:56,392 --> 01:09:59,060
big. But you probably wouldn't want to waste your time

1424
01:09:59,129 --> 01:10:01,228
creating anything bigger than 1024x1024,

1425
01:10:01,297 --> 01:10:04,832
cuz it's gonna be a thumbnail. It's gonna be small showing in

1426
01:10:04,901 --> 01:10:08,802
the files app or whatever, you can return it, so

1427
01:10:08,871 --> 01:10:13,174
we'll do this in the demo on Wednesday as well.

1428
01:10:13,242 --> 01:10:15,442
So there's some other things in UIDocument,

1429
01:10:15,511 --> 01:10:17,845
like localizedName. It will look at the URL, and

1430
01:10:17,913 --> 01:10:20,748
get the name at the end of the URL, and things like that.

1431
01:10:20,817 --> 01:10:23,684
You can find out if you have any unsaved changes currently,

1432
01:10:23,753 --> 01:10:25,953
you can get the date that a file was last saved,

1433
01:10:26,021 --> 01:10:28,555
you can even do userActivity. Which is this thing where

1434
01:10:28,624 --> 01:10:30,624
you start working on something on one device and

1435
01:10:30,693 --> 01:10:32,092
then you go continue on another.

1436
01:10:32,161 --> 01:10:36,396
And you'll be exactly where you were before. So we're out

1437
01:10:36,465 --> 01:10:39,166
of time today, I did have one more topic, which we'll start

1438
01:10:39,235 --> 01:10:42,437
off Wednesday. Which is the UIDocumentBrowserViewControl-

1439
01:10:42,505 --> 01:10:46,507
ler. Which is an awesome way to give a very powerful user

1440
01:10:46,576 --> 01:10:51,446
interface for your user inside your own app. To create files,

1441
01:10:51,514 --> 01:10:55,149
move files, delete files, put them in folders, you know,

1442
01:10:55,218 --> 01:10:58,118
drag them from iCloud drive to your local hard disk.

1443
01:10:58,187 --> 01:11:01,455
All this stuff, you get this powerful UI, very little work

1444
01:11:01,524 --> 01:11:04,659
on your part as long as you have the UIDocument based app.

1445
01:11:04,727 --> 01:11:06,828
So, we'll start off Wednesday, I'll tell you about that.

1446
01:11:06,896 --> 01:11:09,997
And then I'll dive into converting emoji art to be

1447
01:11:10,065 --> 01:11:13,434
a UIDocument based app that uses all of this cool UI and

1448
01:11:13,503 --> 01:11:16,504
all that stuff. Friday, no more sections, so there's no

1449
01:11:16,572 --> 01:11:19,207
Friday section. Next week, I'll be talking about, alerts,

1450
01:11:19,275 --> 01:11:21,809
notifications, I mentioned that, applications lifecycle,

1451
01:11:21,878 --> 01:11:24,912
that app delegate thing. And some more about segues,

1452
01:11:24,981 --> 01:11:27,748
more segues that we haven't talked about as yet.

1453
01:11:27,817 --> 01:11:31,986
So that's all what we're doing next time, all right?

1454
01:11:32,054 --> 01:11:35,656
I will see you then. >> For more, please visit us,
到时候见。>> 更多课程

1455
01:11:35,724 --> 01:11:37,458
at stanford.edu.
详见 stanford.edu