The ForwardingGestureRecognizers to have back reference to the PlatformViewsController so it can access FlutterViewController when its available (#20708)

Author: Chris Yang

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -107,6 +107,10 @@
   flutter_view_controller_.reset([flutter_view_controller retain]);
 }
 
+UIViewController* FlutterPlatformViewsController::getFlutterViewController() {
+  return flutter_view_controller_.get();
+}
+
 void FlutterPlatformViewsController::OnMethodCall(FlutterMethodCall* call, FlutterResult& result) {
   if ([[call method] isEqualToString:@"create"]) {
     OnCreate(call, result);
@@ -161,7 +165,7 @@
 
   FlutterTouchInterceptingView* touch_interceptor = [[[FlutterTouchInterceptingView alloc]
                   initWithEmbeddedView:embedded_view.view
-                 flutterViewController:flutter_view_controller_.get()
+               platformViewsController:GetWeakPtr()
       gestureRecognizersBlockingPolicy:gesture_recognizers_blocking_policies[viewType]]
       autorelease];
 
@@ -701,15 +705,17 @@ - (instancetype)initWithTarget:(id)target
 // directly to the FlutterView.
 @interface ForwardingGestureRecognizer : UIGestureRecognizer <UIGestureRecognizerDelegate>
 - (instancetype)initWithTarget:(id)target
-         flutterViewController:(UIViewController*)flutterViewController;
+       platformViewsController:
+           (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController;
 @end
 
 @implementation FlutterTouchInterceptingView {
   fml::scoped_nsobject<DelayingGestureRecognizer> _delayingRecognizer;
   FlutterPlatformViewGestureRecognizersBlockingPolicy _blockingPolicy;
 }
 - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
-               flutterViewController:(UIViewController*)flutterViewController
+             platformViewsController:
+                 (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController
     gestureRecognizersBlockingPolicy:
         (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy {
   self = [super initWithFrame:embeddedView.frame];
@@ -720,9 +726,9 @@ - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
 
     [self addSubview:embeddedView];
 
-    ForwardingGestureRecognizer* forwardingRecognizer =
-        [[[ForwardingGestureRecognizer alloc] initWithTarget:self
-                                       flutterViewController:flutterViewController] autorelease];
+    ForwardingGestureRecognizer* forwardingRecognizer = [[[ForwardingGestureRecognizer alloc]
+                 initWithTarget:self
+        platformViewsController:std::move(platformViewsController)] autorelease];
 
     _delayingRecognizer.reset([[DelayingGestureRecognizer alloc]
               initWithTarget:self
@@ -833,39 +839,42 @@ - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
 @end
 
 @implementation ForwardingGestureRecognizer {
-  // We can't dispatch events to the framework without this back pointer.
-  // This is a weak reference, the ForwardingGestureRecognizer is owned by the
-  // FlutterTouchInterceptingView which is strong referenced only by the FlutterView,
-  // which is strongly referenced by the FlutterViewController.
-  // So this is safe as when FlutterView is deallocated the reference to ForwardingGestureRecognizer
-  // will go away.
-  UIViewController* _flutterViewController;
+  // Weak reference to FlutterPlatformViewsController. The FlutterPlatformViewsController has
+  // a reference to the FlutterViewController, where we can dispatch pointer events to.
+  //
+  // The lifecycle of FlutterPlatformViewsController is bind to FlutterEngine, which should always
+  // outlives the FlutterViewController. And ForwardingGestureRecognizer is owned by a subview of
+  // FlutterView, so the ForwardingGestureRecognizer never out lives FlutterViewController.
+  // Therefore, `_platformViewsController` should never be nullptr.
+  fml::WeakPtr<flutter::FlutterPlatformViewsController> _platformViewsController;
   // Counting the pointers that has started in one touch sequence.
   NSInteger _currentTouchPointersCount;
 }
 
 - (instancetype)initWithTarget:(id)target
-         flutterViewController:(UIViewController*)flutterViewController {
+       platformViewsController:
+           (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController {
   self = [super initWithTarget:target action:nil];
   if (self) {
     self.delegate = self;
-    _flutterViewController = flutterViewController;
+    FML_DCHECK(platformViewsController.get() != nullptr);
+    _platformViewsController = std::move(platformViewsController);
     _currentTouchPointersCount = 0;
   }
   return self;
 }
 
 - (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_flutterViewController touchesBegan:touches withEvent:event];
+  [_platformViewsController.get()->getFlutterViewController() touchesBegan:touches withEvent:event];
   _currentTouchPointersCount += touches.count;
 }
 
 - (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_flutterViewController touchesMoved:touches withEvent:event];
+  [_platformViewsController.get()->getFlutterViewController() touchesMoved:touches withEvent:event];
 }
 
 - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_flutterViewController touchesEnded:touches withEvent:event];
+  [_platformViewsController.get()->getFlutterViewController() touchesEnded:touches withEvent:event];
   _currentTouchPointersCount -= touches.count;
   // Touches in one touch sequence are sent to the touchesEnded method separately if different
   // fingers stop touching the screen at different time. So one touchesEnded method triggering does
@@ -877,7 +886,8 @@ - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
 }
 
 - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_flutterViewController touchesCancelled:touches withEvent:event];
+  [_platformViewsController.get()->getFlutterViewController() touchesCancelled:touches
+                                                                     withEvent:event];
   _currentTouchPointersCount = 0;
   self.state = UIGestureRecognizerStateFailed;
 }

shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -7,7 +7,9 @@
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterBinaryMessenger.h"
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
 #import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlatformViews.h"
+#import "flutter/shell/platform/darwin/ios/framework/Headers/FlutterViewController.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
+#import "flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController_Internal.h"
 #import "flutter/shell/platform/darwin/ios/platform_view_ios.h"
 #import "third_party/ocmock/Source/OCMock/OCMock.h"
 
@@ -508,6 +510,70 @@ - (void)testClipPath {
   flutterPlatformViewsController->Reset();
 }
 
+- (void)testSetFlutterViewControllerAfterCreateCanStillDispatchTouchEvents {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+  auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/thread_task_runner,
+                               /*raster=*/thread_task_runner,
+                               /*ui=*/thread_task_runner,
+                               /*io=*/thread_task_runner);
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*task_runners=*/runners);
+
+  auto flutterPlatformViewsController = std::make_unique<flutter::FlutterPlatformViewsController>();
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory new] autorelease];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @2, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+
+  XCTAssertNotNil(gMockPlatformView);
+
+  // Find touch inteceptor view
+  UIView* touchInteceptorView = gMockPlatformView;
+  while (touchInteceptorView != nil &&
+         ![touchInteceptorView isKindOfClass:[FlutterTouchInterceptingView class]]) {
+    touchInteceptorView = touchInteceptorView.superview;
+  }
+  XCTAssertNotNil(touchInteceptorView);
+
+  // Find ForwardGestureRecognizer
+  UIGestureRecognizer* forwardGectureRecognizer = nil;
+  for (UIGestureRecognizer* gestureRecognizer in touchInteceptorView.gestureRecognizers) {
+    if ([gestureRecognizer isKindOfClass:NSClassFromString(@"ForwardingGestureRecognizer")]) {
+      forwardGectureRecognizer = gestureRecognizer;
+      break;
+    }
+  }
+
+  // Before setting flutter view controller, events are not dispatched.
+  NSSet* touches1 = OCMClassMock([NSSet class]);
+  UIEvent* event1 = OCMClassMock([UIEvent class]);
+  UIViewController* mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+  [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
+  OCMReject([mockFlutterViewContoller touchesBegan:touches1 withEvent:event1]);
+
+  // Set flutter view controller allows events to be dispatched.
+  NSSet* touches2 = OCMClassMock([NSSet class]);
+  UIEvent* event2 = OCMClassMock([UIEvent class]);
+  flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
+  [forwardGectureRecognizer touchesBegan:touches2 withEvent:event2];
+  OCMVerify([mockFlutterViewContoller touchesBegan:touches2 withEvent:event2]);
+
+  flutterPlatformViewsController->Reset();
+}
+
 - (int)alphaOfPoint:(CGPoint)point onView:(UIView*)view {
   unsigned char pixel[4] = {0};
 

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h

@@ -16,6 +16,8 @@
 #include "flutter/shell/platform/darwin/ios/ios_context.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 
+@class FlutterTouchInterceptingView;
+
 // A UIView that acts as a clipping mask for the |ChildClippingView|.
 //
 // On the [UIView drawRect:] method, this view performs a series of clipping operations and sets the
@@ -43,24 +45,6 @@
 
 @end
 
-// A UIView that is used as the parent for embedded UIViews.
-//
-// This view has 2 roles:
-// 1. Delay or prevent touch events from arriving the embedded view.
-// 2. Dispatching all events that are hittested to the embedded view to the FlutterView.
-@interface FlutterTouchInterceptingView : UIView
-- (instancetype)initWithEmbeddedView:(UIView*)embeddedView
-               flutterViewController:(UIViewController*)flutterViewController
-    gestureRecognizersBlockingPolicy:
-        (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy;
-
-// Stop delaying any active touch sequence (and let it arrive the embedded view).
-- (void)releaseGesture;
-
-// Prevent the touch sequence from ever arriving to the embedded view.
-- (void)blockGesture;
-@end
-
 // The parent view handles clipping to its subviews.
 @interface ChildClippingView : UIView
 
@@ -143,10 +127,14 @@ class FlutterPlatformViewsController {
 
   ~FlutterPlatformViewsController();
 
+  fml::WeakPtr<flutter::FlutterPlatformViewsController> GetWeakPtr();
+
   void SetFlutterView(UIView* flutter_view);
 
   void SetFlutterViewController(UIViewController* flutter_view_controller);
 
+  UIViewController* getFlutterViewController();
+
   void RegisterViewFactory(
       NSObject<FlutterPlatformViewFactory>* factory,
       NSString* factoryId,
@@ -255,6 +243,8 @@ class FlutterPlatformViewsController {
   std::map<std::string, FlutterPlatformViewGestureRecognizersBlockingPolicy>
       gesture_recognizers_blocking_policies;
 
+  std::unique_ptr<fml::WeakPtrFactory<FlutterPlatformViewsController>> weak_factory_;
+
   void OnCreate(FlutterMethodCall* call, FlutterResult& result);
   void OnDispose(FlutterMethodCall* call, FlutterResult& result);
   void OnAcceptGesture(FlutterMethodCall* call, FlutterResult& result);
@@ -313,4 +303,23 @@ class FlutterPlatformViewsController {
 
 }  // namespace flutter
 
+// A UIView that is used as the parent for embedded UIViews.
+//
+// This view has 2 roles:
+// 1. Delay or prevent touch events from arriving the embedded view.
+// 2. Dispatching all events that are hittested to the embedded view to the FlutterView.
+@interface FlutterTouchInterceptingView : UIView
+- (instancetype)initWithEmbeddedView:(UIView*)embeddedView
+             platformViewsController:
+                 (fml::WeakPtr<flutter::FlutterPlatformViewsController>)platformViewsController
+    gestureRecognizersBlockingPolicy:
+        (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy;
+
+// Stop delaying any active touch sequence (and let it arrive the embedded view).
+- (void)releaseGesture;
+
+// Prevent the touch sequence from ever arriving to the embedded view.
+- (void)blockGesture;
+@end
+
 #endif  // FLUTTER_SHELL_PLATFORM_DARWIN_IOS_FRAMEWORK_SOURCE_FLUTTERPLATFORMVIEWS_INTERNAL_H_

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.mm

@@ -24,10 +24,15 @@
 FlutterPlatformViewLayer::~FlutterPlatformViewLayer() = default;
 
 FlutterPlatformViewsController::FlutterPlatformViewsController()
-    : layer_pool_(std::make_unique<FlutterPlatformViewLayerPool>()){};
+    : layer_pool_(std::make_unique<FlutterPlatformViewLayerPool>()),
+      weak_factory_(std::make_unique<fml::WeakPtrFactory<FlutterPlatformViewsController>>(this)){};
 
 FlutterPlatformViewsController::~FlutterPlatformViewsController() = default;
 
+fml::WeakPtr<flutter::FlutterPlatformViewsController> FlutterPlatformViewsController::GetWeakPtr() {
+  return weak_factory_->GetWeakPtr();
+}
+
 CATransform3D GetCATransform3DFromSkMatrix(const SkMatrix& matrix) {
   // Skia only supports 2D transform so we don't map z.
   CATransform3D transform = CATransform3DIdentity;