01-components-and-layout.md

Components and layout

In this session, you'll get started building a pizza store app using Blazor. The app will enable users to order pizzas, customize them, and then track the order deliveries.

Pizza store starting point

We've set up the initial solution for you for the pizza store app in this repo. Go ahead and clone this repo to your machine. You'll find the starting point in the save-points folder along with the end state for each session.

Note: If you copy the code from this workshop to a different location on your machine, be sure to also copy the Directory.Build.props file at the root of this repo in order to restore the appropriate package versions.

The solution already contains four projects:

• BlazingPizza.Client: This is the Blazor project. It contains the UI components for the app.
• BlazingPizza.Server: This is the ASP.NET Core project hosting the Blazor app and also the backend services for the app.
• BlazingPizza.Shared: This project contains the shared model types for the app.
• BlazingPizza.ComponentsLibrary: This is a library of components and helper code to be used by the app in later sessions.

The BlazingPizza.Server project should be set as the startup project.

When you run the app, you'll see that it currently only contains a simple home page.

Open Pages/Index.razor in the BlazingPizza.Client project to see the code for the home page.

@page "/"

<h1>Blazing Pizzas</h1>

The home page is implemented as a single component. The @page directive specifies that the Index component is a routable page with the specified route.

Display the list of pizza specials

First we'll update the home page to display the list of available pizza specials. The list of specials will be part of the state of the Index component.

Add a @code block to Index.razor with a list field to keep track of the available specials:

@code {
    List<PizzaSpecial> specials;
}

The code in the @code block is added to the generated class for the component. The PizzaSpecial type is already defined for you in the BlazingPizza.Shared project.

To get the available list of specials we need to call an API on the backend. Blazor provides a preconfigured HttpClient through dependency injection that is already setup with the correct base address. Use the @inject directive to inject an HttpClient into the Index component.

@page "/"
@inject HttpClient HttpClient

The @inject directive essentially defines a new property on the component where the first token specifies the property type and the second token specifies the property name. The property is populated for you using dependency injection.

Override the OnInitializedAsync method in the @code block to retrieve the list of pizza specials. This method is part of the component lifecycle and is called when the component is initialized. Use the GetFromJsonAsync<T>() method to handle deserializing the response JSON:

@code {
    List<PizzaSpecial> specials;

    protected override async Task OnInitializedAsync()
    {
        specials = await HttpClient.GetFromJsonAsync<List<PizzaSpecial>>("specials", BlazingPizza.OrderContext.Default.ListPizzaSpecial);
    }
}

The /specials API is defined by a minimal API at PizzaApiExtensions.cs in the BlazingPizza.Server project.

See also Create a minimal web API with ASP.NET Core for additional details.

Note: BlazingPizza.OrderContext.Default.ListPizzaSpecial refers to Json serialization with source generators.

Once the component is initialized it will render its markup. Replace the markup in the Index component with the following to list the pizza specials:

<div class="main">
    <ul class="pizza-cards">
        @if (specials != null)
        {
            @foreach (var special in specials)
            {
                <li style="background-image: url('@special.ImageUrl')">
                    <div class="pizza-info">
                        <span class="title">@special.Name</span>
                        @special.Description
                        <span class="price">@special.GetFormattedBasePrice()</span>
                    </div>
                </li>
            }
        }
    </ul>
</div>

Run the app by hitting Ctrl-F5. Now you should see a list of the specials that are available.

Create the layout

Next we'll set up the layout for the app.

Layouts in Blazor are also components. They inherit from LayoutComponentBase, which defines a Body property that can be used to specify where the body of the layout should be rendered. The layout component for our pizza store app is defined in Shared/MainLayout.razor.

@inherits LayoutComponentBase

<div class="content">
    @Body
</div>

To see how the layout is associated with your pages, look at the <Router> component in App.razor. Notice that the DefaultLayout parameter determines the layout used for any page that doesn't specify its own layout directly.

You can also override this DefaultLayout on a per-page basis. To do so, you can add a directive such as @layout SomeOtherLayout at the top of any .razor page component. However, you will not need to do so in this application.

Update the MainLayout component to define a top bar with a branding logo and a nav link for the home page:

@inherits LayoutComponentBase

<div class="top-bar">
    <a class="logo" href="">
        <img src="img/logo.svg" />
    </a>

    <NavLink href="" class="nav-tab" Match="NavLinkMatch.All">
        <img src="img/pizza-slice.svg" />
        <div>Get Pizza</div>
    </NavLink>
</div>

<div class="content">
    @Body
</div>

The NavLink component is provided by Blazor. Components can be used from components by specifying an element with the component's type name along with attributes for any component parameters.

The NavLink component is the same as an anchor tag, except that it adds an active class if the current URL matches the link address. NavLinkMatch.All means that the link should be active only when it matches the entire current URL (not just a prefix). We'll examine the NavLink component in more detail in a later session.

Run the app by hitting Ctrl-F5. With our new layout, our pizza store app now looks like this:

Next up - Customize a pizza