PlatformViewsController always make sure the touch events are finished

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

@@ -871,6 +871,11 @@ @implementation ForwardingGestureRecognizer {
   fml::WeakPtr<flutter::FlutterPlatformViewsController> _platformViewsController;
   // Counting the pointers that has started in one touch sequence.
   NSInteger _currentTouchPointersCount;
+  // We can't dispatch events to the framework without this back pointer.
+  // This gesture recognizer retains the `FlutterViewController` until the
+  // end of a gesture sequence, that is all the touches in touchesBegan are concluded
+  // with |touchesCancelled| or |touchesEnded|.
+  fml::scoped_nsobject<UIViewController> _flutterViewController;
 }
 
 - (instancetype)initWithTarget:(id)target
@@ -887,30 +892,41 @@ - (instancetype)initWithTarget:(id)target
 }
 
 - (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_platformViewsController->getFlutterViewController() touchesBegan:touches withEvent:event];
+  FML_DCHECK(_currentTouchPointersCount >= 0);
+  if (_currentTouchPointersCount == 0) {
+    // At the start of each gesture sequence, we reset the `_flutterViewController`,
+    // so that all the touch events in the same sequence are forwarded to the same
+    // `_flutterViewController`.
+    _flutterViewController.reset([_platformViewsController->getFlutterViewController() retain]);
+  }
+  [_flutterViewController.get() touchesBegan:touches withEvent:event];
   _currentTouchPointersCount += touches.count;
 }
 
 - (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_platformViewsController->getFlutterViewController() touchesMoved:touches withEvent:event];
+  [_flutterViewController.get() touchesMoved:touches withEvent:event];
 }
 
 - (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_platformViewsController->getFlutterViewController() touchesEnded:touches withEvent:event];
+  [_flutterViewController.get() 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
   // not necessarially mean the touch sequence has ended. We Only set the state to
   // UIGestureRecognizerStateFailed when all the touches in the current touch sequence is ended.
   if (_currentTouchPointersCount == 0) {
     self.state = UIGestureRecognizerStateFailed;
+    _flutterViewController.reset(nil);
   }
 }
 
 - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_platformViewsController->getFlutterViewController() touchesCancelled:touches withEvent:event];
-  _currentTouchPointersCount = 0;
-  self.state = UIGestureRecognizerStateFailed;
+  [_flutterViewController.get() touchesCancelled:touches withEvent:event];
+  _currentTouchPointersCount -= touches.count;
+  if (_currentTouchPointersCount == 0) {
+    self.state = UIGestureRecognizerStateFailed;
+    _flutterViewController.reset(nil);
+  }
 }
 
 - (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer

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

@@ -568,6 +568,196 @@ - (void)testSetFlutterViewControllerAfterCreateCanStillDispatchTouchEvents {
   flutterPlatformViewsController->Reset();
 }
 
+- (void)testSetFlutterViewControllerInTheMiddleOfTouchEventShouldStillAllowGesturesToBeHandled {
+  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 flutterPlatformViewsController = std::make_shared<flutter::FlutterPlatformViewsController>();
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners);
+
+  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;
+    }
+  }
+  UIViewController* mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+  {
+    // ***** Sequence 1, finishing touch event with touchEnded ***** //
+
+    flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
+
+    NSSet* touches1 = OCMClassMock([NSSet class]);
+    UIEvent* event1 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
+    OCMVerify([mockFlutterViewContoller touchesBegan:touches1 withEvent:event1]);
+
+    flutterPlatformViewsController->SetFlutterViewController(nil);
+
+    // Allow the touch events to finish
+    NSSet* touches2 = OCMClassMock([NSSet class]);
+    UIEvent* event2 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesMoved:touches2 withEvent:event2];
+    OCMVerify([mockFlutterViewContoller touchesMoved:touches2 withEvent:event2]);
+
+    NSSet* touches3 = OCMClassMock([NSSet class]);
+    UIEvent* event3 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches3 withEvent:event3];
+    OCMVerify([mockFlutterViewContoller touchesEnded:touches3 withEvent:event3]);
+
+    // Now the 2nd touch sequence should not be allowed.
+    NSSet* touches4 = OCMClassMock([NSSet class]);
+    UIEvent* event4 = OCMClassMock([UIEvent class]);
+    mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+    [forwardGectureRecognizer touchesBegan:touches4 withEvent:event4];
+    OCMReject([mockFlutterViewContoller touchesBegan:touches4 withEvent:event4]);
+
+    NSSet* touches5 = OCMClassMock([NSSet class]);
+    UIEvent* event5 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches5 withEvent:event5];
+    OCMReject([mockFlutterViewContoller touchesEnded:touches5 withEvent:event5]);
+  }
+
+  {
+    // ***** Sequence 2, finishing touch event with touchCancelled ***** //
+    flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
+
+    NSSet* touches1 = OCMClassMock([NSSet class]);
+    UIEvent* event1 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
+    OCMVerify([mockFlutterViewContoller touchesBegan:touches1 withEvent:event1]);
+
+    flutterPlatformViewsController->SetFlutterViewController(nil);
+
+    // Allow the touch events to finish
+    NSSet* touches2 = OCMClassMock([NSSet class]);
+    UIEvent* event2 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesMoved:touches2 withEvent:event2];
+    OCMVerify([mockFlutterViewContoller touchesMoved:touches2 withEvent:event2]);
+
+    NSSet* touches3 = OCMClassMock([NSSet class]);
+    UIEvent* event3 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesCancelled:touches3 withEvent:event3];
+    OCMVerify([mockFlutterViewContoller touchesCancelled:touches3 withEvent:event3]);
+
+    // Now the 2nd touch sequence should not be allowed.
+    NSSet* touches4 = OCMClassMock([NSSet class]);
+    UIEvent* event4 = OCMClassMock([UIEvent class]);
+    mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+    [forwardGectureRecognizer touchesBegan:touches4 withEvent:event4];
+    OCMReject([mockFlutterViewContoller touchesBegan:touches4 withEvent:event4]);
+
+    NSSet* touches5 = OCMClassMock([NSSet class]);
+    UIEvent* event5 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches5 withEvent:event5];
+    OCMReject([mockFlutterViewContoller touchesEnded:touches5 withEvent:event5]);
+  }
+
+  {
+    // ***** Sequence 3, multile touches in one sequence with setting flutter view controllers in
+    // between ***** //
+    flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
+
+    NSSet* touches1 = OCMClassMock([NSSet class]);
+    OCMStub([touches1 count]).andReturn(1);
+    UIEvent* event1 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
+    OCMVerify([mockFlutterViewContoller touchesBegan:touches1 withEvent:event1]);
+
+    UIViewController* mockFlutterViewContoller2 = OCMClassMock([UIViewController class]);
+    flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller2);
+
+    // Touch events should still send to the old FlutterViewController if FlutterViewController
+    // is updated in between.
+    NSSet* touches2 = OCMClassMock([NSSet class]);
+    OCMStub([touches2 count]).andReturn(1);
+    UIEvent* event2 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesBegan:touches2 withEvent:event2];
+    OCMVerify([mockFlutterViewContoller touchesBegan:touches2 withEvent:event2]);
+    OCMReject([mockFlutterViewContoller2 touchesBegan:touches2 withEvent:event2]);
+
+    NSSet* touches3 = OCMClassMock([NSSet class]);
+    OCMStub([touches3 count]).andReturn(1);
+    UIEvent* event3 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesMoved:touches3 withEvent:event3];
+    OCMVerify([mockFlutterViewContoller touchesMoved:touches3 withEvent:event3]);
+    OCMReject([mockFlutterViewContoller2 touchesMoved:touches3 withEvent:event3]);
+
+    NSSet* touches4 = OCMClassMock([NSSet class]);
+    OCMStub([touches4 count]).andReturn(1);
+    UIEvent* event4 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches4 withEvent:event4];
+    OCMVerify([mockFlutterViewContoller touchesEnded:touches4 withEvent:event4]);
+    OCMReject([mockFlutterViewContoller2 touchesEnded:touches4 withEvent:event4]);
+
+    NSSet* touches5 = OCMClassMock([NSSet class]);
+    OCMStub([touches5 count]).andReturn(1);
+    UIEvent* event5 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches5 withEvent:event5];
+    OCMVerify([mockFlutterViewContoller touchesEnded:touches5 withEvent:event5]);
+    OCMReject([mockFlutterViewContoller2 touchesEnded:touches5 withEvent:event5]);
+
+    // Now the 2nd touch sequence should go to the new FlutterViewController
+
+    NSSet* touches6 = OCMClassMock([NSSet class]);
+    OCMStub([touches6 count]).andReturn(1);
+    UIEvent* event6 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesBegan:touches6 withEvent:event6];
+    OCMVerify([mockFlutterViewContoller2 touchesBegan:touches6 withEvent:event6]);
+    OCMReject([mockFlutterViewContoller touchesBegan:touches6 withEvent:event6]);
+
+    // Allow the touch events to finish
+    NSSet* touches7 = OCMClassMock([NSSet class]);
+    OCMStub([touches7 count]).andReturn(1);
+    UIEvent* event7 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesMoved:touches7 withEvent:event7];
+    OCMVerify([mockFlutterViewContoller2 touchesMoved:touches7 withEvent:event7]);
+    OCMReject([mockFlutterViewContoller touchesMoved:touches7 withEvent:event7]);
+
+    NSSet* touches8 = OCMClassMock([NSSet class]);
+    OCMStub([touches8 count]).andReturn(1);
+    UIEvent* event8 = OCMClassMock([UIEvent class]);
+    [forwardGectureRecognizer touchesEnded:touches8 withEvent:event8];
+    OCMVerify([mockFlutterViewContoller2 touchesEnded:touches8 withEvent:event8]);
+    OCMReject([mockFlutterViewContoller touchesEnded:touches8 withEvent:event8]);
+  }
+
+  flutterPlatformViewsController->Reset();
+}
+
 - (void)testFlutterPlatformViewControllerSubmitFrameWithoutFlutterViewNotCrashing {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");