Some changes to allow for external toolkit support on android

src/Android/Avalonia.Android/AvaloniaMainActivity.cs

@@ -9,11 +9,11 @@ using AndroidX.Lifecycle;
 
 namespace Avalonia.Android
 {
-    public abstract class AvaloniaMainActivity : AppCompatActivity
+    public abstract class AvaloniaMainActivity : AppCompatActivity, IActivityResultHandler
     {
         internal static object ViewContent;
 
-        internal Action<int, Result, Intent> ActivityResult;
+        public Action<int, Result, Intent> ActivityResult { get; set; }
         internal AvaloniaView View;
 
         protected override void OnCreate(Bundle savedInstanceState)
@@ -24,8 +24,6 @@ namespace Avalonia.Android
                 View.Content = ViewContent;
             }
 
-            View.Prepare();
-
             if (Avalonia.Application.Current.ApplicationLifetime is SingleViewLifetime lifetime)
             {
                 lifetime.View = View;

src/Android/Avalonia.Android/AvaloniaView.cs

@@ -21,10 +21,7 @@ namespace Avalonia.Android
         {
             _view = new ViewImpl(this);
             AddView(_view.View);
-        }
 
-        internal void Prepare ()
-        {
             _root = new EmbeddableControlRoot(_view);
             _root.Prepare();
         }

src/Android/Avalonia.Android/IActivityResultHandler.cs

@@ -0,0 +1,11 @@
+using System;
+using Android.App;
+using Android.Content;
+
+namespace Avalonia.Android
+{
+    public interface IActivityResultHandler
+    {
+        public Action<int, Result, Intent> ActivityResult { get; set; }
+    }
+}

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -1,6 +1,6 @@
 using System;
 using System.Collections.Generic;
-
+using Android.App;
 using Android.Content;
 using Android.Graphics;
 using Android.Runtime;
@@ -52,7 +52,7 @@ namespace Avalonia.Android.Platform.SkiaPlatform
                 _view.Resources.DisplayMetrics.HeightPixels).ToSize(RenderScaling);
 
             NativeControlHost = new AndroidNativeControlHostImpl(avaloniaView);
-            StorageProvider = new AndroidStorageProvider((AvaloniaMainActivity)avaloniaView.Context);
+            StorageProvider = new AndroidStorageProvider((Activity)avaloniaView.Context);
         }
 
         public virtual Point GetAvaloniaPointFromEvent(MotionEvent e, int pointerIndex) =>

src/Android/Avalonia.Android/Platform/Storage/AndroidStorageProvider.cs

@@ -14,10 +14,10 @@ namespace Avalonia.Android.Platform.Storage;
 
 internal class AndroidStorageProvider : IStorageProvider
 {
-    private readonly AvaloniaMainActivity _activity;
+    private readonly Activity _activity;
     private int _lastRequestCode = 20000;
 
-    public AndroidStorageProvider(AvaloniaMainActivity activity)
+    public AndroidStorageProvider(Activity activity)
     {
         _activity = activity;
     }
@@ -119,7 +119,10 @@ internal class AndroidStorageProvider : IStorageProvider
         var tcs = new TaskCompletionSource<Intent?>();
         var currentRequestCode = _lastRequestCode++;
 
-        _activity.ActivityResult += OnActivityResult;
+        if (_activity is IActivityResultHandler mainActivity)
+        {
+            mainActivity.ActivityResult += OnActivityResult;
+        }
         _activity.StartActivityForResult(pickerIntent, currentRequestCode);
 
         var result = await tcs.Task;
@@ -158,7 +161,11 @@ internal class AndroidStorageProvider : IStorageProvider
                 return;
             }
 
-            _activity.ActivityResult -= OnActivityResult;
+
+            if (_activity is IActivityResultHandler mainActivity)
+            {
+                mainActivity.ActivityResult -= OnActivityResult;
+            }
 
             _ = tcs.TrySetResult(resultCode == Result.Ok ? data : null);
         }