Consider allowing primary window definition via the MAUI startup overloaded method as `UseMauiApp<TApp, TWindow>()`

[egvijayanand]

Description

Consider allowing primary window definition via the MAUI startup overloaded method as UseMauiApp<TApp, TWindow>()

Public API Changes

var builder = MauiApp.CreateBuilder();
// MainWindow will be primary window of the app
builder.UseMauiApp<App, MainWindow>();
return builder.Build();

Intended Use-Case

This would streamline the Application's code-behind file and more closely integrate the primary Window with the App.

[egvijayanand]

I've devised a solution to make this work.

Overriding the CreateWindow() method in the App code-behind file is no longer required.

As a bonus, since the Window type is DI resolved, it can take parameters as well.

Kindly let me know your feedback, and I will submit a PR for this change.

public static class MauiAppBuilderExtensions
{
    // Updated extension method.
    public static MauiAppBuilder UseMauiApp<TApp, TWindow>(this MauiAppBuilder builder)
        where TApp : class, IApplication, new()
        where TWindow : Window
    {
        // Invoke the usual method and register the two other services in the pipeline.
        builder.UseMauiApp<TApp>();
        builder.Services.AddSingleton<TWindow>();
        builder.Services.AddSingleton<IWindowCreator, WindowCreator<TWindow>>();
        return builder;
    }
}

// This independent generic type needs to be housed somewhere
public class WindowCreator<TWindow>(IServiceProvider services) : IWindowCreator
    where TWindow : Window
{
    public Window CreateWindow(Application app, IActivationState? activationState)
        => services.GetRequiredService<TWindow>();
}

// Finally, invoke this new method in the startup pipeline.
var builder = MauiApp.CreateBuilder();
// Integrate both the App and the Window in a single method call.
builder.UseMauiApp<App, MainWindow>();
// All other stuff
return builder.Build();

[egvijayanand]

This generic WindowCreator<TWindow> type can also be defined as internal provided that this type and the extension method are in the same assembly.

[egvijayanand]

RFC @davidortinau