android - cancel back callbacks when handled (#20452)

src/Android/Avalonia.Android/AvaloniaActivity.cs

@@ -29,6 +29,7 @@ public class AvaloniaActivity : AppCompatActivity, IAvaloniaActivity
     private bool _contentViewSet;
     internal AvaloniaView? _view;
     private BackPressedCallback? _currentBackPressedCallback;
+    private bool _shouldNavigateBack;
 
     public Action<int, Result, Intent?>? ActivityResult { get; set; }
     public Action<int, string[], Permission[]>? RequestPermissionsResult { get; set; }
@@ -65,6 +66,20 @@ public class AvaloniaActivity : AppCompatActivity, IAvaloniaActivity
         }
     }
 
+    /// <summary>
+    /// Gets whether to call the default back handler after our back handler is called.
+    /// </summary>
+    internal bool ShouldNavigateBack
+    {
+        get
+        {
+            var goBack = _shouldNavigateBack;
+            _shouldNavigateBack = false;
+
+            return goBack;
+        }
+    }
+
     event EventHandler<ActivatedEventArgs>? IAvaloniaActivity.Activated
     {
         add { _onActivated += value; }
@@ -214,6 +229,8 @@ public class AvaloniaActivity : AppCompatActivity, IAvaloniaActivity
         var eventArgs = new AndroidBackRequestedEventArgs();
 
         BackRequested?.Invoke(this, eventArgs);
+
+        _shouldNavigateBack = !eventArgs.Handled;
     }
 
     private class GlobalLayoutListener : Java.Lang.Object, ViewTreeObserver.IOnGlobalLayoutListener

src/Android/Avalonia.Android/BackPressedCallback.cs

@@ -10,6 +10,14 @@ namespace Avalonia.Android
         public override void HandleOnBackPressed()
         {
             activity.OnBackInvoked();
+
+            if (activity.ShouldNavigateBack)
+            {
+                this.Enabled = false;
+                activity.OnBackPressedDispatcher?.OnBackPressed();
+            }
+
+            this.Enabled = true;
         }
     }
 }