Support basic back navigation in Android 13/API 33

shell/platform/android/io/flutter/embedding/android/FlutterActivity.java

@@ -35,6 +35,8 @@
 import android.view.View;
 import android.view.Window;
 import android.view.WindowManager;
+import android.window.OnBackInvokedCallback;
+import android.window.OnBackInvokedDispatcher;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
@@ -495,13 +497,57 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
 
     lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
 
+    registerOnBackInvokedCallback();
+
     configureWindowForTransparency();
 
     setContentView(createFlutterView());
 
     configureStatusBarForFullscreenFlutterExperience();
   }
 
+  /**
+   * Registers the callback with OnBackInvokedDispatcher to capture back navigation gestures and
+   * pass them to the framework.
+   *
+   * <p>This replaces the deprecated onBackPressed method override in order to support API 33's
+   * predictive back navigation feature.
+   *
+   * <p>The callback must be unregistered in order to prevent unpredictable behavior once outside
+   * the Flutter app.
+   */
+  @VisibleForTesting
+  public void registerOnBackInvokedCallback() {
+    if (Build.VERSION.SDK_INT >= 33) {
+      getOnBackInvokedDispatcher()
+          .registerOnBackInvokedCallback(
+              OnBackInvokedDispatcher.PRIORITY_DEFAULT, onBackInvokedCallback);
+    }
+  }
+
+  /**
+   * Unregisters the callback from OnBackInvokedDispatcher.
+   *
+   * <p>This should be called when the activity is no longer in use to prevent unpredictable
+   * behavior such as being stuck and unable to press back.
+   */
+  @VisibleForTesting
+  public void unregisterOnBackInvokedCallback() {
+    if (Build.VERSION.SDK_INT >= 33) {
+      getOnBackInvokedDispatcher().unregisterOnBackInvokedCallback(onBackInvokedCallback);
+    }
+  }
+
+  private final OnBackInvokedCallback onBackInvokedCallback =
+      Build.VERSION.SDK_INT >= 33
+          ? new OnBackInvokedCallback() {
+            @Override
+            public void onBackInvoked() {
+              onBackPressed();
+            }
+          }
+          : null;
+
   /**
    * Switches themes for this {@code Activity} from the theme used to launch this {@code Activity}
    * to a "normal theme" that is intended for regular {@code Activity} operation.
@@ -680,7 +726,9 @@ protected void onSaveInstanceState(Bundle outState) {
    *
    * <p>After calling, this activity should be disposed immediately and not be re-used.
    */
-  private void release() {
+  @VisibleForTesting
+  public void release() {
+    unregisterOnBackInvokedCallback();
     if (delegate != null) {
       delegate.release();
       delegate = null;

shell/platform/android/test/io/flutter/embedding/android/FlutterActivityTest.java

@@ -88,6 +88,36 @@ public void flutterViewHasId() {
     assertTrue(activity.findViewById(FlutterActivity.FLUTTER_VIEW_ID) instanceof FlutterView);
   }
 
+  // TODO(garyq): Robolectric does not yet support android api 33 yet. Switch to a robolectric
+  // test that directly exercises the OnBackInvoked APIs when API 33 is supported.
+  @Test
+  @TargetApi(33)
+  public void itRegistersOnBackInvokedCallbackOnCreate() {
+    Intent intent = FlutterActivityWithReportFullyDrawn.createDefaultIntent(ctx);
+    ActivityController<FlutterActivityWithReportFullyDrawn> activityController =
+        Robolectric.buildActivity(FlutterActivityWithReportFullyDrawn.class, intent);
+    FlutterActivityWithReportFullyDrawn activity = spy(activityController.get());
+
+    activity.onCreate(null);
+
+    verify(activity, times(1)).registerOnBackInvokedCallback();
+  }
+
+  // TODO(garyq): Robolectric does not yet support android api 33 yet. Switch to a robolectric
+  // test that directly exercises the OnBackInvoked APIs when API 33 is supported.
+  @Test
+  @TargetApi(33)
+  public void itUnregistersOnBackInvokedCallbackOnRelease() {
+    Intent intent = FlutterActivityWithReportFullyDrawn.createDefaultIntent(ctx);
+    ActivityController<FlutterActivityWithReportFullyDrawn> activityController =
+        Robolectric.buildActivity(FlutterActivityWithReportFullyDrawn.class, intent);
+    FlutterActivityWithReportFullyDrawn activity = spy(activityController.get());
+
+    activity.release();
+
+    verify(activity, times(1)).unregisterOnBackInvokedCallback();
+  }
+
   @Test
   public void itCreatesDefaultIntentWithExpectedDefaults() {
     Intent intent = FlutterActivity.createDefaultIntent(ctx);
@@ -596,6 +626,14 @@ public void resetFullyDrawn() {
     }
   }
 
+  private class FlutterActivityWithMockBackInvokedHandling extends FlutterActivity {
+    @Override
+    public void registerOnBackInvokedCallback() {}
+
+    @Override
+    public void unregisterOnBackInvokedCallback() {}
+  }
+
   private static final class FakeFlutterPlugin
       implements FlutterPlugin,
           ActivityAware,

shell/platform/android/test_runner/build.gradle

@@ -71,10 +71,10 @@ android {
     testImplementation "com.google.android.play:core:1.8.0"
     testImplementation "com.ibm.icu:icu4j:69.1"
     testImplementation "org.robolectric:robolectric:4.7.3"
-    testImplementation "junit:junit:4.13"
-    testImplementation "androidx.test.ext:junit:1.1.3"
+    testImplementation "junit:junit:4.13.2"
+    testImplementation "androidx.test.ext:junit:1.1.4-alpha07"
 
-    def mockitoVersion = "4.1.0"
+    def mockitoVersion = "4.7.0"
     testImplementation "org.mockito:mockito-core:$mockitoVersion"
     testImplementation "org.mockito:mockito-inline:$mockitoVersion"
     testImplementation "org.mockito:mockito-android:$mockitoVersion"