Platform channel for predictive back

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

@@ -217,6 +217,8 @@ public class FlutterActivity extends Activity
     implements FlutterActivityAndFragmentDelegate.Host, LifecycleOwner {
   private static final String TAG = "FlutterActivity";
 
+  private boolean hasRegisteredBackCallback = false;
+
   /**
    * The ID of the {@code FlutterView} created by this activity.
    *
@@ -643,8 +645,6 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
 
     lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
 
-    registerOnBackInvokedCallback();
-
     configureWindowForTransparency();
 
     setContentView(createFlutterView());
@@ -668,6 +668,7 @@ public void registerOnBackInvokedCallback() {
       getOnBackInvokedDispatcher()
           .registerOnBackInvokedCallback(
               OnBackInvokedDispatcher.PRIORITY_DEFAULT, onBackInvokedCallback);
+      hasRegisteredBackCallback = true;
     }
   }
 
@@ -681,6 +682,7 @@ public void registerOnBackInvokedCallback() {
   public void unregisterOnBackInvokedCallback() {
     if (Build.VERSION.SDK_INT >= 33) {
       getOnBackInvokedDispatcher().unregisterOnBackInvokedCallback(onBackInvokedCallback);
+      hasRegisteredBackCallback = false;
     }
   }
 
@@ -698,6 +700,15 @@ public void onBackInvoked() {
           }
           : null;
 
+  @Override
+  public void setFrameworkHandlesBack(boolean frameworkHandlesBacks) {
+    if (frameworkHandlesBacks && !hasRegisteredBackCallback) {
+      registerOnBackInvokedCallback();
+    } else if (!frameworkHandlesBacks && hasRegisteredBackCallback) {
+      unregisterOnBackInvokedCallback();
+    }
+  }
+
   /**
    * 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.

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

@@ -1689,6 +1689,11 @@ boolean shouldDelayFirstAndroidViewDraw() {
     return getArguments().getBoolean(ARG_SHOULD_DELAY_FIRST_ANDROID_VIEW_DRAW);
   }
 
+  @Override
+  public void setFrameworkHandlesBack(boolean frameworkHandlesBacks) {
+    // Irrelevant to FlutterFragment.
+  }
+
   private boolean stillAttachedForEvent(String event) {
     if (delegate == null) {
       Log.w(TAG, "FlutterFragment " + hashCode() + " " + event + " called after release.");

shell/platform/android/io/flutter/embedding/engine/systemchannels/PlatformChannel.java

@@ -136,6 +136,13 @@ public void onMethodCall(@NonNull MethodCall call, @NonNull MethodChannel.Result
                   result.error("error", exception.getMessage(), null);
                 }
                 break;
+              case "SystemNavigator.setFrameworkHandlesBack":
+                {
+                  boolean frameworkHandlesBacks = (boolean) arguments;
+                  platformMessageHandler.setFrameworkHandlesBack(frameworkHandlesBacks);
+                  result.success(null);
+                  break;
+                }
               case "SystemNavigator.pop":
                 platformMessageHandler.popSystemNavigator();
                 result.success(null);
@@ -509,6 +516,9 @@ public interface PlatformMessageHandler {
      */
     void setSystemUiOverlayStyle(@NonNull SystemChromeStyle systemUiOverlayStyle);
 
+    /** The Flutter application would or would not like to handle navigation pop events itself. */
+    void setFrameworkHandlesBack(boolean frameworkHandlesBack);
+
     /**
      * The Flutter application would like to pop the top item off of the Android app's navigation
      * back stack.

shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java

@@ -56,6 +56,8 @@ public interface PlatformPluginDelegate {
      *     androidx.activity.OnBackPressedDispatcher} will be executed.
      */
     boolean popSystemNavigator();
+
+    void setFrameworkHandlesBack(boolean frameworkHandlesBacks);
   }
 
   @VisibleForTesting
@@ -109,6 +111,11 @@ public void setSystemUiOverlayStyle(
           setSystemChromeSystemUIOverlayStyle(systemUiOverlayStyle);
         }
 
+        @Override
+        public void setFrameworkHandlesBack(boolean frameworkHandlesBacks) {
+          PlatformPlugin.this.setFrameworkHandlesBack(frameworkHandlesBacks);
+        }
+
         @Override
         public void popSystemNavigator() {
           PlatformPlugin.this.popSystemNavigator();
@@ -475,6 +482,10 @@ private void setSystemChromeSystemUIOverlayStyle(
     currentTheme = systemChromeStyle;
   }
 
+  private void setFrameworkHandlesBack(boolean frameworkHandlesBacks) {
+    platformPluginDelegate.setFrameworkHandlesBack(frameworkHandlesBacks);
+  }
+
   private void popSystemNavigator() {
     if (platformPluginDelegate != null && platformPluginDelegate.popSystemNavigator()) {
       // A custom behavior was executed by the delegate. Don't execute default behavior.

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

@@ -92,14 +92,20 @@ public void flutterViewHasId() {
   // test that directly exercises the OnBackInvoked APIs when API 33 is supported.
   @Test
   @TargetApi(33)
-  public void itRegistersOnBackInvokedCallbackOnCreate() {
+  public void itRegistersOnBackInvokedCallbackOnChangingFrameworkHandlesBack() {
     Intent intent = FlutterActivityWithReportFullyDrawn.createDefaultIntent(ctx);
     ActivityController<FlutterActivityWithReportFullyDrawn> activityController =
         Robolectric.buildActivity(FlutterActivityWithReportFullyDrawn.class, intent);
     FlutterActivityWithReportFullyDrawn activity = spy(activityController.get());
 
     activity.onCreate(null);
 
+    verify(activity, times(0)).registerOnBackInvokedCallback();
+
+    activity.setFrameworkHandlesBack(false);
+    verify(activity, times(0)).registerOnBackInvokedCallback();
+
+    activity.setFrameworkHandlesBack(true);
     verify(activity, times(1)).registerOnBackInvokedCallback();
   }
 

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

@@ -417,5 +417,8 @@ public void updateSystemUiOverlays() {}
     public boolean popSystemNavigator() {
       return false;
     }
+
+    @Override
+    public void setFrameworkHandlesBack(boolean frameworkHandlesBacks) {}
   }
 }

shell/platform/android/test/io/flutter/plugin/platform/PlatformPluginTest.java

@@ -469,6 +469,19 @@ public void verifyWindowFlagsSetToStyleOverlays() {
                 | WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION);
   }
 
+  @Test
+  public void setFrameworkHandlesBackFlutterActivity() {
+    Activity mockActivity = mock(Activity.class);
+    PlatformChannel mockPlatformChannel = mock(PlatformChannel.class);
+    PlatformPluginDelegate mockPlatformPluginDelegate = mock(PlatformPluginDelegate.class);
+    PlatformPlugin platformPlugin =
+        new PlatformPlugin(mockActivity, mockPlatformChannel, mockPlatformPluginDelegate);
+
+    platformPlugin.mPlatformMessageHandler.setFrameworkHandlesBack(true);
+
+    verify(mockPlatformPluginDelegate, times(1)).setFrameworkHandlesBack(true);
+  }
+
   @Test
   public void popSystemNavigatorFlutterActivity() {
     Activity mockActivity = mock(Activity.class);