predictive back gesture support for Android 13+ (#32461)

* Add predictive back gesture support for Android 13+

Introduces a unified HandleBackNavigation method to centralize back navigation handling and integrates Android 13+ predictive back gesture callbacks with MAUI lifecycle events. Predictive back is registered and unregistered appropriately, ensuring custom back handling works with system back gesture animation.

* Fix predictive back callback registration and resource management

- Fix potential double registration by checking if callback is null before creating/registering
- Add Dispose() call in OnDestroy() to prevent memory leaks
- Change field type to concrete PredictiveBackCallback for better performance (CA1859)
- Add comment explaining PRIORITY_DEFAULT value

These changes address code review feedback while maintaining the PR's core functionality.

* Simplify code to reduce nesting

---------

Co-authored-by: Matthew Leibowitz <mattleibow@live.com>

Author: 2 people

src/Core/src/Platform/Android/MauiAppCompatActivity.Lifecycle.cs

@@ -27,18 +27,7 @@ protected override void OnActivityResult(int requestCode, Result resultCode, Int
 		public override void OnBackPressed()
 #pragma warning restore 809
 		{
-			var preventBackPropagation = false;
-			IPlatformApplication.Current?.Services?.InvokeLifecycleEvents<AndroidLifecycle.OnBackPressed>(del =>
-			{
-				preventBackPropagation = del(this) || preventBackPropagation;
-			});
-
-			if (!preventBackPropagation)
-#pragma warning disable CA1416 // Validate platform compatibility
-#pragma warning disable CA1422 // Validate platform compatibility
-				base.OnBackPressed();
-#pragma warning restore CA1422 // Validate platform compatibility
-#pragma warning restore CA1416 // Validate platform compatibility
+			HandleBackNavigation();
 		}
 
 		public override void OnConfigurationChanged(Configuration newConfig)
@@ -145,5 +134,21 @@ public override bool OnKeyUp(Keycode keyCode, KeyEvent? e)
 
 			return handled || base.OnKeyUp(keyCode, e);
 		}
+
+		/// <summary>
+		/// Central handler used by both legacy <see cref="OnBackPressed"/> and the Android 13+ predictive back gesture callback.
+		/// Implements lifecycle event invocation and default back stack propagation unless explicitly prevented.
+		/// </summary>
+		void HandleBackNavigation()
+		{
+			var preventBackPropagation = false;
+			IPlatformApplication.Current?.Services?.InvokeLifecycleEvents<AndroidLifecycle.OnBackPressed>(del =>
+			{
+				preventBackPropagation = del(this) || preventBackPropagation;
+			});
+
+			if (!preventBackPropagation)
+				base.OnBackPressed();
+		}
 	}
 }

src/Core/src/Platform/Android/MauiAppCompatActivity.cs

@@ -1,5 +1,7 @@
+using System;
 using Android.OS;
 using Android.Views;
+using Android.Window;
 using AndroidX.Activity;
 using AndroidX.AppCompat.App;
 using AndroidX.Core.Content.Resources;
@@ -30,10 +32,28 @@ protected override void OnCreate(Bundle? savedInstanceState)
 			{
 				this.CreatePlatformWindow(IPlatformApplication.Current.Application, savedInstanceState);
 			}
+
+			// Register predictive back callback (Android 13+/API 33+) if available.
+			// This integrates MAUI lifecycle OnBackPressed events with the system back gesture animation.
+			// Guidance: route custom back handling through AndroidX OnBackPressedDispatcher so
+			// predictive back works correctly:
+			// https://developer.android.com/guide/navigation/custom-back/predictive-back-gesture#update-custom
+			if (OperatingSystem.IsAndroidVersionAtLeast(33) && _predictiveBackCallback is null)
+			{
+				_predictiveBackCallback = new PredictiveBackCallback(this);
+				// Priority 0 = PRIORITY_DEFAULT: callback invoked only when no higher-priority callback handles the event
+				OnBackInvokedDispatcher?.RegisterOnBackInvokedCallback(0, _predictiveBackCallback);
+			}
 		}
 
 		protected override void OnDestroy()
 		{
+			if (OperatingSystem.IsAndroidVersionAtLeast(33) && _predictiveBackCallback is not null)
+			{
+				OnBackInvokedDispatcher?.UnregisterOnBackInvokedCallback(_predictiveBackCallback);
+				_predictiveBackCallback.Dispose();
+				_predictiveBackCallback = null;
+			}
 			base.OnDestroy();
 		}
 
@@ -52,5 +72,22 @@ public override bool DispatchTouchEvent(MotionEvent? e)
 
 			return handled || implHandled;
 		}
+
+		PredictiveBackCallback? _predictiveBackCallback;
+
+		sealed class PredictiveBackCallback : Java.Lang.Object, IOnBackInvokedCallback
+		{
+			readonly MauiAppCompatActivity _activity;
+			public PredictiveBackCallback(MauiAppCompatActivity activity)
+			{
+				_activity = activity;
+			}
+
+			public void OnBackInvoked()
+			{
+				// Reuse unified handling (will invoke lifecycle events and conditionally propagate).
+				_activity.HandleBackNavigation();
+			}
+		}
 	}
 }