Fixed memory leaks within FlutterFragment and FlutterView (flutter#34268, flutter#34269, flutter#34270). (flutter#9288)

Author: matthew-carroll

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

@@ -607,6 +607,7 @@ public void onDetach() {
 
     // Null out the platformPlugin to avoid a possible retain cycle between the plugin, this Fragment,
     // and this Fragment's Activity.
+    platformPlugin.destroy();
     platformPlugin = null;
 
     // Destroy our FlutterEngine if we're not set to retain it.

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

@@ -561,11 +561,16 @@ public void detachFromFlutterEngine() {
     }
     Log.d(TAG, "Detaching from Flutter Engine");
 
+    // Disconnect and clean up the AccessibilityBridge.
+    accessibilityBridge.release();
+    accessibilityBridge = null;
+
     // Inform the Android framework that it should retrieve a new InputConnection
     // now that the engine is detached. The new InputConnection will be null, which
     // signifies that this View does not process input (until a new engine is attached).
     // TODO(mattcarroll): once this is proven to work, move this line ot TextInputPlugin
     textInputPlugin.getInputMethodManager().restartInput(this);
+    textInputPlugin.destroy();
 
     // Instruct our FlutterRenderer that we are no longer interested in being its RenderSurface.
     didRenderFirstFrame = false;

shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java

@@ -46,7 +46,7 @@ public class TextInputPlugin {
     // target is a platform view. See the comments on lockPlatformViewInputConnection for more details.
     private boolean isInputConnectionLocked;
 
-    // TODO(mattcarroll): change @Nullable to @NonNull once new embedding integrates PlatformViewsController.
+    // TODO(mattcarroll): change @Nullable to @NonNull once new embedding integrates PlatformViewsController (#34286).
     public TextInputPlugin(View view, @NonNull DartExecutor dartExecutor, @Nullable PlatformViewsController platformViewsController) {
         mView = view;
         mImm = (InputMethodManager) view.getContext().getSystemService(
@@ -85,7 +85,7 @@ public void clearClient() {
             }
         });
         this.platformViewsController = platformViewsController;
-        // TODO(mattcarroll): remove if-statement once new embedding integrates PlatformViewsController.
+        // TODO(mattcarroll): remove if-statement once new embedding integrates PlatformViewsController (#34286).
         if (platformViewsController != null) {
             platformViewsController.attachTextInputPlugin(this);
         }
@@ -127,7 +127,7 @@ public void unlockPlatformViewInputConnection() {
      * The TextInputPlugin instance should not be used after calling this.
      */
     public void destroy() {
-        // TODO(mattcarroll): Remove if-statement once new embedding integrates PlatformViewsController.
+        // TODO(mattcarroll): Remove if-statement once new embedding integrates PlatformViewsController (#34286).
         if (platformViewsController != null) {
             platformViewsController.detachTextInputPlugin();
         }

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

@@ -94,6 +94,15 @@ public PlatformPlugin(Activity activity, PlatformChannel platformChannel) {
         mEnabledOverlays = DEFAULT_SYSTEM_UI;
     }
 
+    /**
+     * Releases all resources held by this {@code PlatformPlugin}.
+     * <p>
+     * Do not invoke any methods on a {@code PlatformPlugin} after invoking this method.
+     */
+    public void destroy() {
+        this.platformChannel.setPlatformMessageHandler(null);
+    }
+
     private void playSystemSound(PlatformChannel.SoundType soundType) {
         if (soundType == PlatformChannel.SoundType.CLICK) {
             View view = activity.getWindow().getDecorView();