Fixed stored @State properties on App

[Amzd]

Steps

• Add your name or username and a link to your GitHub profile into the Contributors.md file.
• Build the project on your machine. If it does not compile, fix the errors.
• Describe the purpose and approach of your pull request below.
• Submit the pull request. Thank you very much for your contribution!

Purpose

Currently when using a State property with storage on App instead of on a View, the app ID was accessed before it was set, causing the State internals to look for the data in the folder temporary/ which usually doesn't exist because at the time you will be writing into the State the app ID will be set and it writes the value into app.id/ folder.

This happened because when the State property is on App it is initialized before GTUIApp.appID is set.

struct ExampleApp: App {
    let id = "me.amzd.Example"
    var app: GTUIApp!

    /// This State will try to read its value for the key example from disk before we can access `id`
    /// (because we need to initialize ExampleApp to access the id property)
    @State("example") var example: String?
    
    // ...
}

Approach

I fixed this by making the App.id property static and forwarding it to GTUIApp.appID first thing the program does. I have also made the GTUIApp.appID force unwrapped optional so regression of this issue is not possible.

I am open to suggestions of how to fix this differently. You can also fix this yourself in a different way without crediting, it is not that complicated.

Since it is a breaking change I still need to update the examples

[david-swift]

Thanks for opening the dicussion and already providing a potential solution! I prefer not to require the user to add a static variable, so I'll see whether I can make the state variables load the files after initializing the app structure. Otherwise, I'll merge your implementation.

[david-swift]

Instead of reading the app id at the initialization of a state variable, it will now read it as soon as the value is accessed for the first time. That way, the id property can stay on an app's instance.