Why does MainActivity base.OnCreate() fail for Android when a Custom Renderer is enabled with UseMauiCompatibility() in MauiProgram.cs?

Question

I am migrating Xamarin code to .NET MAUI and I followed @David Ortinau Wiki on Custom Renderers as described here.

The custom renderer is for the Shellcontrol and whenUseMauiCompatibility()is activated in MauiProgram.cs, anInvalidCastExceptionis thrown inMainActivity` as shown below.

Any help is appreciated as to what causes this and any workaround for this issue.

• .NET MAUI: ver 6.0.486
• Platform: Android
• Visual Studio: ver 17.3.0 Preview 6.0

UPDATE

I did some inspection of program flow from debugging Call Stack and here is more info:

When rendering is activated, the execution of base.OnCreate(savedInstanceState); in the OnCreate(Bundle savedInstanceState) goes to the renderer constructor (line #3 below). It is on return from initializing the ShellCustomRenderer class that the exception is thrown.

The ShellRenderer is from Microsoft.Maui.Controls.Handlers.Compatibility namespace and I cannot spot where the invalid casting is taking place between hitting base.OnCreate(savedInstanceState); and initializing the renderer class ShellCustomRenderer below.

public class ShellCustomRenderer : ShellRenderer  
{  
    public ShellCustomRenderer(Context context) : base(context)  
    {  

    }  

    protected override IShellToolbarAppearanceTracker CreateToolbarAppearanceTracker()  
    {  
        return new CustomToolbarTracker();   // CustomToolbarTracker class not shown here for brevity  
    }  
}  

Answer 1

Hello,​

If you want to use custom renderer for shell in MAUI, you can register shell handler in MauiProgram.cs like following code

   builder  
   	.UseMauiApp<App>()  
               .ConfigureMauiHandlers(handlers => {  
   			#if ANDROID  
                   handlers.AddHandler(typeof(Shell), typeof(ShellCustomRenderer));  
   			#endif  
               })  

Best Regards,

Leon Lu

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