Added FlutterActivity and FlutterFragment hook to cleanUpFlutterEngin…

…e() as symmetry for configureFlutterEngine(). (flutter#41943) (flutter#12987)

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

@@ -851,6 +851,17 @@ public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
     // No-op. Hook for subclasses.
   }
 
+  /**
+   * Hook for the host to cleanup references that were established in
+   * {@link #configureFlutterEngine(FlutterEngine)} before the host is destroyed or detached.
+   * <p>
+   * This method is called in {@link #onDestroy()}.
+   */
+  @Override
+  public void cleanUpFlutterEngine(@NonNull FlutterEngine flutterEngine) {
+    // No-op. Hook for subclasses.
+  }
+
   /**
    * Hook for subclasses to control whether or not the {@link FlutterFragment} within this
    * {@code Activity} automatically attaches its {@link FlutterEngine} to this {@code Activity}.

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

@@ -421,6 +421,10 @@ void onDetach() {
     Log.v(TAG, "onDetach()");
     ensureAlive();
 
+    // Give the host an opportunity to cleanup any references that were created in
+    // configureFlutterEngine().
+    host.cleanUpFlutterEngine(flutterEngine);
+
     if (host.shouldAttachEngineToActivity()) {
       // Notify plugins that they are no longer attached to an Activity.
       Log.d(TAG, "Detaching FlutterEngine from the Activity that owns this Fragment.");
@@ -693,6 +697,12 @@ private void ensureAlive() {
      */
     void configureFlutterEngine(@NonNull FlutterEngine flutterEngine);
 
+    /**
+     * Hook for the host to cleanup references that were established in
+     * {@link #configureFlutterEngine(FlutterEngine)} before the host is destroyed or detached.
+     */
+    void cleanUpFlutterEngine(@NonNull FlutterEngine flutterEngine);
+
     /**
      * Returns true if the {@link FlutterEngine}'s plugin system should be connected to the
      * host {@link Activity}, allowing plugins to interact with it.

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

@@ -30,4 +30,10 @@ public interface FlutterEngineConfigurator {
    * {@code Activity} at the time that this method is invoked.
    */
   void configureFlutterEngine(@NonNull FlutterEngine flutterEngine);
+
+  /**
+   * Cleans up references that were established in {@link #configureFlutterEngine(FlutterEngine)}
+   * before the host is destroyed or detached.
+   */
+  void cleanUpFlutterEngine(@NonNull FlutterEngine flutterEngine);
 }

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

@@ -924,6 +924,20 @@ public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
     }
   }
 
+  /**
+   * Hook for the host to cleanup references that were established in
+   * {@link #configureFlutterEngine(FlutterEngine)} before the host is destroyed or detached.
+   * <p>
+   * This method is called in {@link #onDetach()}.
+   */
+  @Override
+  public void cleanUpFlutterEngine(@NonNull FlutterEngine flutterEngine) {
+    FragmentActivity attachedActivity = getActivity();
+    if (attachedActivity instanceof FlutterEngineConfigurator) {
+      ((FlutterEngineConfigurator) attachedActivity).cleanUpFlutterEngine(flutterEngine);
+    }
+  }
+
   /**
    * See {@link NewEngineFragmentBuilder#shouldAttachEngineToActivity()} and
    * {@link CachedEngineFragmentBuilder#shouldAttachEngineToActivity()}.

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

@@ -550,6 +550,17 @@ public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
     // No-op. Hook for subclasses.
   }
 
+  /**
+   * Hook for the host to cleanup references that were established in
+   * {@link #configureFlutterEngine(FlutterEngine)} before the host is destroyed or detached.
+   * <p>
+   * This method is called in {@link #onDestroy()}.
+   */
+  @Override
+  public void cleanUpFlutterEngine(@NonNull FlutterEngine flutterEngine) {
+    // No-op. Hook for subclasses.
+  }
+
   /**
    * The path to the bundle that contains this Flutter app's resources, e.g., Dart code snapshots.
    * <p>

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

@@ -197,6 +197,21 @@ public void itGivesHostAnOpportunityToConfigureFlutterEngine() {
     verify(mockHost, times(1)).configureFlutterEngine(mockFlutterEngine);
   }
 
+  @Test
+  public void itGivesHostAnOpportunityToCleanUpFlutterEngine() {
+    // ---- Test setup ----
+    // Create the real object that we're testing.
+    FlutterActivityAndFragmentDelegate delegate = new FlutterActivityAndFragmentDelegate(mockHost);
+
+    // --- Execute the behavior under test ---
+    // The FlutterEngine is created in onAttach().
+    delegate.onAttach(RuntimeEnvironment.application);
+    delegate.onDetach();
+
+    // Verify that the host was asked to configure our FlutterEngine.
+    verify(mockHost, times(1)).cleanUpFlutterEngine(mockFlutterEngine);
+  }
+
   @Test
   public void itSendsInitialRouteToFlutter() {
     // ---- Test setup ----