MAUI dependency services + Prism

[nk-alex]

This probably is going to be a banal question, but I was not able to find any tutorial addressing this issue and I'm not able to figure it out myself.

I'm migrating my Xamarin.Forms app to MAUI. The time to migrate the dependency services has arrived. Here is a little sample:

Definition & implementations of my class

//Main Project
public interface IApplicationVersion
{
    String GetApplicationVersion();
}

//Platforms.iOS
public class ApplicationVersion : IApplicationVersion
{
	public string GetApplicationVersion()
	{
		return NSBundle.MainBundle.InfoDictionary[new NSString("CFBundleVersion")].ToString();
	}
}

//Platforms.Android
public class ApplicationVersion : IApplicationVersion
{
	Context CurrentContext => Microsoft.Maui.ApplicationModel.Platform.CurrentActivity;

	public String GetApplicationVersion()
	{
		return CurrentContext.PackageManager.GetPackageInfo(CurrentContext.PackageName, 0).VersionName;
	}
}

My MAUI program now, looks like this:

public static MauiApp CreateMauiApp()
{
    var builder = MauiApp.CreateBuilder();
    builder
        .UsePrismApp<App>(PrismStartup.Configure)
   	 .UseMauiCommunityToolkit()
   	 .UseLocalizationResourceManager(resource =>
   		{
   			resource.AddResource(Resources.Localization.AppResources.ResourceManager);
   		})
   	 .UseFFImageLoading()
   	 .ConfigureFonts(fonts =>
        	{
            	fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
            	fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
        	});

   builder.Services.AddTransient<IApplicationVersion, ApplicationVersion>();
   var app = builder.Build();

   return app;
}

This is my PrismStartup page looking like:

internal static class PrismStartup
{
    public static void Configure(PrismAppBuilder builder)
    {
        builder.RegisterTypes(RegisterTypes).OnAppStart("LoginPage");
    }

    private static void RegisterTypes(IContainerRegistry containerRegistry)
    {
		containerRegistry.RegisterForNavigation<LoginPage, LoginPageViewModel>()
			 .RegisterInstance(SemanticScreenReader.Default);
		containerRegistry.RegisterForNavigation<MainPage, MainPageViewModel>()
                     .RegisterInstance(SemanticScreenReader.Default);
    }
}

Finally, this is how I'm requesting my IApplicationVersion from my viewModel:

public LoginPageViewModel(IApplicationVersion applicationVersion, INavigationService navigationService, IPageDialogService dialogService) : base(navigationService)
{ 
	var tmp = applicationVersion.GetApplicationVersion();
}

But my LoginPage view model constructor it's always called before builder.Build();, so, even requesting IApplicationVersion from its constructor, I only receive a null instance.

What I'm doing wrong?

[dansiegel]

    private static void RegisterTypes(IContainerRegistry containerRegistry)
    {
		containerRegistry.RegisterForNavigation<LoginPage, LoginPageViewModel>()
			 .RegisterInstance(SemanticScreenReader.Default);
		containerRegistry.RegisterForNavigation<MainPage, MainPageViewModel>()
                     .RegisterInstance(SemanticScreenReader.Default);
    }

One thing to note you don't need to be calling .RegisterInstance(SemanticScreenReader.Default); after each time you register a page.

Without a reproduction it's hard to say what's happening but there is nothing that Prism is doing that would should cause the LoginPageViewModel to be resolved before the .Build() is called.

[nk-alex]

You are right. Prism working as expected. I transitioned that Android implementation from my Xamarin project following MAUI docs and expected it to work the same way. Silly me