Custom Control Library and specifying handlers

I have a custom MAUI control library that I use across several projects. I've been turning it into a NuGet library to make reuse easier.

Within this library is a custom ContentPage (call it ModalPage) that has an accompanying custom handler (call it ModalPageHandler) that derives from PageHandler and performs some magic on iOS/MacCatalyst. In my apps, I register this using the standard builder call to ConfigureMauiHandlers in MauiProgram.cs:

builder.ConfigureMauiHandlers(handlers => {
    handlers.AddHandler(typeof(ModalPage), typeof(ModalPageHandler));
});

Everything works as expected.

However within the context of a control library, there is no access to the MauiAppBuilder in the main app as it's already been built.

How do I configure my control library so that the ModalPageHandler is the default handler being used without the consumer registering it? It must be possible as MAUI controls do it...I just can't find documentation on that linkage.

Currently, Must do a work-around

Add to library an Init(builder) function that must be called from MauiProgram.CreateMauiApp() in every app that uses your library:

public static MauiApp CreateMauiApp()
{
  var builder = ...;
  ...
  MyLib.Init(builder);   // Every app must do this, or your handlers/DI-injected-services won't work correctly.
  ...
  builder.Build();
}

In the library:

public static void Init(MauiAppBuilder builder)
{
  builder.ConfigureMauiHandlers(handlers => {
    handlers.AddHandler(typeof(ModalPage), typeof(ModalPageHandler));
  });

builder.Services.AddSingleton<MyCustomComponent>();
}

That's less obtrusive than having to explicitly refer to the handlers themselves.

BONUS - (failed) ATTEMPT - ALMOST POSSIBLE, JUST NEED ONE MISSING METHOD

Attempt to add handler in page class static constructor.

In the library:

public partial class MyPage : ContentPage
{
    // ONE-TIME initialization.
    public static MyPage()
    {
		IMauiHandlersFactory handlersFactory = Application.Current.Handler?.MauiContext?.Handlers;
		if (handlersFactory != null) {
            // Compile error: No such method.
			// TODO: No method exists to add handlers. They can only be added by MauiAppBuilder.
            handlersFactory.AddHandler(typeof(ModalPage), typeof(ModalPageHandler));
		}
    }
}

Unfortunately, the Interfaces available after MauiAppBuilder.Build() runs, only have getters; I don't see any way to add another handler.

TODO: I didn't investigate, to find out whether the runtime object (of handlersFactory) is a class that has such a method. If so, a (not guaranteed to work in future) work-around is to cast factory to that class. Then propose that the method be made available on the interface.

First of all, you can add the handler directly after you added the reference of the library. Such as:

.ConfigureMauiHandlers(handlers =>
     {
#if ANDROID
       handlers.AddHandler(typeof(MauiLib1.NewPage1), typeof(MauiLib1.Platforms.Android.MyHandler));
#endif
     });

And my project structure:

In addition, you can also use the ContentPage's OnHandlerChanged method to custom the content page instead of using the custom handler.