iOS Platform View: Fixed overrelease of the observer. (#13093)

Author: gaaclarke

shell/platform/darwin/ios/platform_view_ios.h

@@ -48,6 +48,20 @@ class PlatformViewIOS final : public PlatformView {
   void SetSemanticsEnabled(bool enabled) override;
 
  private:
+  /// Smart pointer for use with objective-c observers.
+  /// This guarentees we remove the observer.
+  class ScopedObserver {
+   public:
+    ScopedObserver();
+    ~ScopedObserver();
+    void reset(id<NSObject> observer);
+    ScopedObserver(const ScopedObserver&) = delete;
+    ScopedObserver& operator=(const ScopedObserver&) = delete;
+
+   private:
+    id<NSObject> observer_;
+  };
+
   fml::WeakPtr<FlutterViewController> owner_controller_;
   // Since the `ios_surface_` is created on the platform thread but
   // used on the GPU thread we need to protect it with a mutex.
@@ -58,7 +72,7 @@ class PlatformViewIOS final : public PlatformView {
   std::unique_ptr<AccessibilityBridge> accessibility_bridge_;
   fml::scoped_nsprotocol<FlutterTextInputPlugin*> text_input_plugin_;
   fml::closure firstFrameCallback_;
-  fml::scoped_nsprotocol<NSObject*> dealloc_view_controller_observer_;
+  ScopedObserver dealloc_view_controller_observer_;
 
   // |PlatformView|
   void HandlePlatformMessage(fml::RefPtr<flutter::PlatformMessage> message) override;

shell/platform/darwin/ios/platform_view_ios.mm

@@ -54,15 +54,15 @@
 
   // Add an observer that will clear out the owner_controller_ ivar and
   // the accessibility_bridge_ in case the view controller is deleted.
-  dealloc_view_controller_observer_.reset([[NSNotificationCenter defaultCenter]
-      addObserverForName:FlutterViewControllerWillDealloc
-                  object:owner_controller_.get()
-                   queue:[NSOperationQueue mainQueue]
-              usingBlock:^(NSNotification* note) {
-                // Implicit copy of 'this' is fine.
-                accessibility_bridge_.reset();
-                owner_controller_.reset();
-              }]);
+  dealloc_view_controller_observer_.reset(
+      [[[NSNotificationCenter defaultCenter] addObserverForName:FlutterViewControllerWillDealloc
+                                                         object:owner_controller_.get()
+                                                          queue:[NSOperationQueue mainQueue]
+                                                     usingBlock:^(NSNotification* note) {
+                                                       // Implicit copy of 'this' is fine.
+                                                       accessibility_bridge_.reset();
+                                                       owner_controller_.reset();
+                                                     }] retain]);
 
   if (owner_controller_) {
     ios_surface_ =
@@ -174,4 +174,23 @@ new AccessibilityBridge(static_cast<FlutterView*>(owner_controller_.get().view),
   text_input_plugin_ = plugin;
 }
 
+PlatformViewIOS::ScopedObserver::ScopedObserver() : observer_(nil) {}
+
+PlatformViewIOS::ScopedObserver::~ScopedObserver() {
+  if (observer_) {
+    [[NSNotificationCenter defaultCenter] removeObserver:observer_];
+    [observer_ release];
+  }
+}
+
+void PlatformViewIOS::ScopedObserver::reset(id<NSObject> observer) {
+  if (observer != observer_) {
+    if (observer_) {
+      [[NSNotificationCenter defaultCenter] removeObserver:observer_];
+      [observer_ release];
+    }
+    observer_ = observer;
+  }
+}
+
 }  // namespace flutter