Always set change type to cancel with touchesCancelled on iOS platform view (#24333)

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

@@ -15,6 +15,7 @@
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterOverlayView.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/ios_surface.h"
 #import "flutter/shell/platform/darwin/ios/ios_surface_gl.h"
 
@@ -938,7 +939,12 @@ void FlutterPlatformViewsController::ResetFrameState() {
 }
 
 - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
-  [_flutterViewController.get() touchesCancelled:touches withEvent:event];
+  // In the event of platform view is removed, iOS generates a "stationary" change type instead of
+  // "cancelled" change type.
+  // Flutter needs all the cancelled touches to be "cancelled" change types in order to correctly
+  // handle gesture sequence.
+  // We always override the change type to "cancelled".
+  [((FlutterViewController*)_flutterViewController.get()) forceTouchesCancelled:touches];
   _currentTouchPointersCount -= touches.count;
   if (_currentTouchPointersCount == 0) {
     self.state = UIGestureRecognizerStateFailed;

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

@@ -626,7 +626,7 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
   // Before setting flutter view controller, events are not dispatched.
   NSSet* touches1 = [[[NSSet alloc] init] autorelease];
   id event1 = OCMClassMock([UIEvent class]);
-  id mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+  id mockFlutterViewContoller = OCMClassMock([FlutterViewController class]);
   [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
   OCMReject([mockFlutterViewContoller touchesBegan:touches1 withEvent:event1]);
 
@@ -684,7 +684,7 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
       break;
     }
   }
-  id mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+  id mockFlutterViewContoller = OCMClassMock([FlutterViewController class]);
   {
     // ***** Sequence 1, finishing touch event with touchEnded ***** //
     flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
@@ -739,7 +739,7 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
     NSSet* touches3 = [[[NSSet alloc] init] autorelease];
     id event3 = OCMClassMock([UIEvent class]);
     [forwardGectureRecognizer touchesCancelled:touches3 withEvent:event3];
-    OCMVerify([mockFlutterViewContoller touchesCancelled:touches3 withEvent:event3]);
+    OCMVerify([mockFlutterViewContoller forceTouchesCancelled:touches3]);
 
     // Now the 2nd touch sequence should not be allowed.
     NSSet* touches4 = [[[NSSet alloc] init] autorelease];
@@ -803,7 +803,7 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
       break;
     }
   }
-  id mockFlutterViewContoller = OCMClassMock([UIViewController class]);
+  id mockFlutterViewContoller = OCMClassMock([FlutterViewController class]);
 
   flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
 
@@ -866,6 +866,66 @@ fml::RefPtr<fml::TaskRunner> CreateNewThread(std::string name) {
   flutterPlatformViewsController->Reset();
 }
 
+- (void)testFlutterPlatformViewTouchesCancelledEventAreForcedToBeCancelled {
+  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;
+    }
+  }
+  id mockFlutterViewContoller = OCMClassMock([FlutterViewController class]);
+
+  flutterPlatformViewsController->SetFlutterViewController(mockFlutterViewContoller);
+
+  NSSet* touches1 = [NSSet setWithObject:@1];
+  id event1 = OCMClassMock([UIEvent class]);
+  [forwardGectureRecognizer touchesBegan:touches1 withEvent:event1];
+
+  [forwardGectureRecognizer touchesCancelled:touches1 withEvent:event1];
+  OCMVerify([mockFlutterViewContoller forceTouchesCancelled:touches1]);
+
+  flutterPlatformViewsController->Reset();
+}
+
 - (void)testFlutterPlatformViewControllerSubmitFrameWithoutFlutterViewNotCrashing {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");

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

@@ -947,6 +947,11 @@ static flutter::PointerData::DeviceKind DeviceKindFromTouchType(UITouch* touch)
   [self dispatchTouches:touches pointerDataChangeOverride:nullptr];
 }
 
+- (void)forceTouchesCancelled:(NSSet*)touches {
+  flutter::PointerData::Change cancel = flutter::PointerData::Change::kCancel;
+  [self dispatchTouches:touches pointerDataChangeOverride:&cancel];
+}
+
 #pragma mark - Handle view resizing
 
 - (void)updateViewportMetrics {

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

@@ -29,6 +29,9 @@ extern NSNotificationName const FlutterViewControllerShowHomeIndicator;
 - (fml::WeakPtr<FlutterViewController>)getWeakPtr;
 - (std::shared_ptr<flutter::FlutterPlatformViewsController>&)platformViewsController;
 - (FlutterRestorationPlugin*)restorationPlugin;
+// Send touches to the Flutter Engine while forcing the change type to be cancelled.
+// The `phase`s in `touches` are ignored.
+- (void)forceTouchesCancelled:(NSSet*)touches;
 
 @end