iOS platform view gesture blocking policy. (#15940)

Author: Chris Yang

shell/platform/darwin/ios/framework/Headers/FlutterPlugin.h

@@ -238,6 +238,32 @@ typedef void (*FlutterPluginRegistrantCallback)(NSObject<FlutterPluginRegistry>*
 - (void)detachFromEngineForRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar;
 @end
 
+#pragma mark -
+/***************************************************************************************************
+ * How the UIGestureRecognizers of a platform view are blocked.
+ *
+ * UIGestureRecognizers of platform views can be blocked based on decisions made by the
+ * Flutter Framework (e.g. When an interact-able widget is covering the platform view).
+ */
+typedef enum {
+  /**
+   * Flutter blocks all the UIGestureRecognizers on the platform view as soon as it
+   * decides they should be blocked.
+   *
+   * With this policy, only the `touchesBegan` method for all the UIGestureRecognizers is guaranteed
+   * to be called.
+   */
+  FlutterPlatformViewGestureRecognizersBlockingPolicyEager,
+  /**
+   * Flutter blocks the platform view's UIGestureRecognizers from recognizing only after
+   * touchesEnded was invoked.
+   *
+   * This results in the platform view's UIGestureRecognizers seeing the entire touch sequence,
+   * but never recognizing the gesture (and never invoking actions).
+   */
+  FlutterPlatformViewGestureRecognizersBlockingPolicyWaitUntilTouchesEnded,
+} FlutterPlatformViewGestureRecognizersBlockingPolicy;
+
 #pragma mark -
 /***************************************************************************************************
  *Registration context for a single `FlutterPlugin`, providing a one stop shop
@@ -277,6 +303,23 @@ typedef void (*FlutterPluginRegistrantCallback)(NSObject<FlutterPluginRegistry>*
 - (void)registerViewFactory:(NSObject<FlutterPlatformViewFactory>*)factory
                      withId:(NSString*)factoryId;
 
+/**
+ * Registers a `FlutterPlatformViewFactory` for creation of platform views.
+ *
+ * Plugins can expose a `UIView` for embedding in Flutter apps by registering a view factory.
+ *
+ * @param factory The view factory that will be registered.
+ * @param factoryId A unique identifier for the factory, the Dart code of the Flutter app can use
+ *   this identifier to request creation of a `UIView` by the registered factory.
+ * @param gestureBlockingPolicy How UIGestureRecognizers on the platform views are
+ * blocked.
+ *
+ */
+- (void)registerViewFactory:(NSObject<FlutterPlatformViewFactory>*)factory
+                              withId:(NSString*)factoryId
+    gestureRecognizersBlockingPolicy:
+        (FlutterPlatformViewGestureRecognizersBlockingPolicy)gestureRecognizersBlockingPolicy;
+
 /**
  * Publishes a value for external use of the plugin.
  *

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

@@ -761,7 +761,17 @@ - (NSString*)lookupKeyForAsset:(NSString*)asset fromPackage:(NSString*)package {
 
 - (void)registerViewFactory:(NSObject<FlutterPlatformViewFactory>*)factory
                      withId:(NSString*)factoryId {
-  [_flutterEngine platformViewsController] -> RegisterViewFactory(factory, factoryId);
+  [self registerViewFactory:factory
+                                withId:factoryId
+      gestureRecognizersBlockingPolicy:FlutterPlatformViewGestureRecognizersBlockingPolicyEager];
+}
+
+- (void)registerViewFactory:(NSObject<FlutterPlatformViewFactory>*)factory
+                              withId:(NSString*)factoryId
+    gestureRecognizersBlockingPolicy:
+        (FlutterPlatformViewGestureRecognizersBlockingPolicy)gestureRecognizersBlockingPolicy {
+  [_flutterEngine platformViewsController] -> RegisterViewFactory(factory, factoryId,
+                                                                  gestureRecognizersBlockingPolicy);
 }
 
 @end

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

@@ -86,8 +86,10 @@
   views_[viewId] = fml::scoped_nsobject<NSObject<FlutterPlatformView>>([embedded_view retain]);
 
   FlutterTouchInterceptingView* touch_interceptor = [[[FlutterTouchInterceptingView alloc]
-       initWithEmbeddedView:embedded_view.view
-      flutterViewController:flutter_view_controller_.get()] autorelease];
+                  initWithEmbeddedView:embedded_view.view
+                 flutterViewController:flutter_view_controller_.get()
+      gestureRecognizersBlockingPolicy:gesture_recognizers_blocking_policies[viewType]]
+      autorelease];
 
   touch_interceptors_[viewId] =
       fml::scoped_nsobject<FlutterTouchInterceptingView>([touch_interceptor retain]);
@@ -149,11 +151,13 @@
 
 void FlutterPlatformViewsController::RegisterViewFactory(
     NSObject<FlutterPlatformViewFactory>* factory,
-    NSString* factoryId) {
+    NSString* factoryId,
+    FlutterPlatformViewGestureRecognizersBlockingPolicy gestureRecognizerBlockingPolicy) {
   std::string idString([factoryId UTF8String]);
   FML_CHECK(factories_.count(idString) == 0);
   factories_[idString] =
       fml::scoped_nsobject<NSObject<FlutterPlatformViewFactory>>([factory retain]);
+  gesture_recognizers_blocking_policies[idString] = gestureRecognizerBlockingPolicy;
 }
 
 void FlutterPlatformViewsController::SetFrameSize(SkISize frame_size) {
@@ -513,6 +517,15 @@
 // invoking an acceptGesture method on the platform_views channel). And this is how we allow the
 // Flutter framework to delay or prevent the embedded view from getting a touch sequence.
 @interface DelayingGestureRecognizer : UIGestureRecognizer <UIGestureRecognizerDelegate>
+
+// Indicates that if the `DelayingGestureRecognizer`'s state should be set to
+// `UIGestureRecognizerStateEnded` during next `touchesEnded` call.
+@property(nonatomic) bool shouldEndInNextTouchesEnded;
+
+// Indicates that the `DelayingGestureRecognizer`'s `touchesEnded` has been invoked without
+// setting the state to `UIGestureRecognizerStateEnded`.
+@property(nonatomic) bool touchedEndedWithoutBlocking;
+
 - (instancetype)initWithTarget:(id)target
                         action:(SEL)action
           forwardingRecognizer:(UIGestureRecognizer*)forwardingRecognizer;
@@ -535,9 +548,12 @@ - (instancetype)initWithTarget:(id)target
 
 @implementation FlutterTouchInterceptingView {
   fml::scoped_nsobject<DelayingGestureRecognizer> _delayingRecognizer;
+  FlutterPlatformViewGestureRecognizersBlockingPolicy _blockingPolicy;
 }
 - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
-               flutterViewController:(UIViewController*)flutterViewController {
+               flutterViewController:(UIViewController*)flutterViewController
+    gestureRecognizersBlockingPolicy:
+        (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy {
   self = [super initWithFrame:embeddedView.frame];
   if (self) {
     self.multipleTouchEnabled = YES;
@@ -554,6 +570,7 @@ - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
               initWithTarget:self
                       action:nil
         forwardingRecognizer:forwardingRecognizer]);
+    _blockingPolicy = blockingPolicy;
 
     [self addGestureRecognizer:_delayingRecognizer.get()];
     [self addGestureRecognizer:forwardingRecognizer];
@@ -566,7 +583,27 @@ - (void)releaseGesture {
 }
 
 - (void)blockGesture {
-  _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
+  switch (_blockingPolicy) {
+    case FlutterPlatformViewGestureRecognizersBlockingPolicyEager:
+      // We block all other gesture recognizers immediately in this policy.
+      _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
+      break;
+    case FlutterPlatformViewGestureRecognizersBlockingPolicyWaitUntilTouchesEnded:
+      if (_delayingRecognizer.get().touchedEndedWithoutBlocking) {
+        // If touchesEnded of the `DelayingGesureRecognizer` has been already invoked,
+        // we want to set the state of the `DelayingGesureRecognizer` to
+        // `UIGestureRecognizerStateEnded` as soon as possible.
+        _delayingRecognizer.get().state = UIGestureRecognizerStateEnded;
+      } else {
+        // If touchesEnded of the `DelayingGesureRecognizer` has not been invoked,
+        // We will set a flag to notify the `DelayingGesureRecognizer` to set the state to
+        // `UIGestureRecognizerStateEnded` when touchesEnded is called.
+        _delayingRecognizer.get().shouldEndInNextTouchesEnded = YES;
+      }
+      break;
+    default:
+      break;
+  }
 }
 
 // We want the intercepting view to consume the touches and not pass the touches up to the parent
@@ -596,7 +633,10 @@ - (instancetype)initWithTarget:(id)target
   self = [super initWithTarget:target action:action];
   if (self) {
     self.delaysTouchesBegan = YES;
+    self.delaysTouchesEnded = YES;
     self.delegate = self;
+    self.shouldEndInNextTouchesEnded = NO;
+    self.touchedEndedWithoutBlocking = NO;
     _forwardingRecognizer.reset([forwardingRecognizer retain]);
   }
   return self;
@@ -614,6 +654,21 @@ - (BOOL)gestureRecognizer:(UIGestureRecognizer*)gestureRecognizer
   return otherGestureRecognizer == self;
 }
 
+- (void)touchesBegan:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+  self.touchedEndedWithoutBlocking = NO;
+  [super touchesBegan:touches withEvent:event];
+}
+
+- (void)touchesEnded:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+  if (self.shouldEndInNextTouchesEnded) {
+    self.state = UIGestureRecognizerStateEnded;
+    self.shouldEndInNextTouchesEnded = NO;
+  } else {
+    self.touchedEndedWithoutBlocking = YES;
+  }
+  [super touchesEnded:touches withEvent:event];
+}
+
 - (void)touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event {
   self.state = UIGestureRecognizerStateFailed;
 }

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

@@ -11,6 +11,7 @@
 #include "flutter/shell/platform/darwin/common/framework/Headers/FlutterBinaryMessenger.h"
 #include "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
 #include "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlatformViews.h"
+#include "flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlugin.h"
 
 // A UIView that is used as the parent for embedded UIViews.
 //
@@ -19,7 +20,9 @@
 // 2. Dispatching all events that are hittested to the embedded view to the FlutterView.
 @interface FlutterTouchInterceptingView : UIView
 - (instancetype)initWithEmbeddedView:(UIView*)embeddedView
-               flutterViewController:(UIViewController*)flutterViewController;
+               flutterViewController:(UIViewController*)flutterViewController
+    gestureRecognizersBlockingPolicy:
+        (FlutterPlatformViewGestureRecognizersBlockingPolicy)blockingPolicy;
 
 // Stop delaying any active touch sequence (and let it arrive the embedded view).
 - (void)releaseGesture;
@@ -80,7 +83,10 @@ class FlutterPlatformViewsController {
 
   void SetFlutterViewController(UIViewController* flutter_view_controller);
 
-  void RegisterViewFactory(NSObject<FlutterPlatformViewFactory>* factory, NSString* factoryId);
+  void RegisterViewFactory(
+      NSObject<FlutterPlatformViewFactory>* factory,
+      NSString* factoryId,
+      FlutterPlatformViewGestureRecognizersBlockingPolicy gestureRecognizerBlockingPolicy);
 
   void SetFrameSize(SkISize frame_size);
 
@@ -152,6 +158,10 @@ class FlutterPlatformViewsController {
   // Only compoiste platform views in this set.
   std::unordered_set<int64_t> views_to_recomposite_;
 
+  // The FlutterPlatformViewGestureRecognizersBlockingPolicy for each type of platform view.
+  std::map<std::string, FlutterPlatformViewGestureRecognizersBlockingPolicy>
+      gesture_recognizers_blocking_policies;
+
   std::map<int64_t, std::unique_ptr<SkPictureRecorder>> picture_recorders_;
 
   void OnCreate(FlutterMethodCall* call, FlutterResult& result);

testing/scenario_app/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java

@@ -0,0 +1,23 @@
+package io.flutter.plugins;
+
+import io.flutter.plugin.common.PluginRegistry;
+
+/**
+ * Generated file. Do not edit.
+ */
+public final class GeneratedPluginRegistrant {
+  public static void registerWith(PluginRegistry registry) {
+    if (alreadyRegisteredWith(registry)) {
+      return;
+    }
+  }
+
+  private static boolean alreadyRegisteredWith(PluginRegistry registry) {
+    final String key = GeneratedPluginRegistrant.class.getCanonicalName();
+    if (registry.hasPlugin(key)) {
+      return true;
+    }
+    registry.registrarFor(key);
+    return false;
+  }
+}

testing/scenario_app/ios/Runner/GeneratedPluginRegistrant.h

@@ -0,0 +1,17 @@
+//
+//  Generated file. Do not edit.
+//
+
+#ifndef GeneratedPluginRegistrant_h
+#define GeneratedPluginRegistrant_h
+
+#import <Flutter/Flutter.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface GeneratedPluginRegistrant : NSObject
++ (void)registerWithRegistry:(NSObject<FlutterPluginRegistry>*)registry;
+@end
+
+NS_ASSUME_NONNULL_END
+#endif /* GeneratedPluginRegistrant_h */

testing/scenario_app/ios/Runner/GeneratedPluginRegistrant.m

@@ -0,0 +1,12 @@
+//
+//  Generated file. Do not edit.
+//
+
+#import "GeneratedPluginRegistrant.h"
+
+@implementation GeneratedPluginRegistrant
+
++ (void)registerWithRegistry:(NSObject<FlutterPluginRegistry>*)registry {
+}
+
+@end

testing/scenario_app/ios/Scenarios/Scenarios.xcodeproj/project.pbxproj

@@ -50,6 +50,7 @@
 		6816DBAC2318696600A51400 /* golden_platform_view_opacity_iPhone SE_simulator.png in Resources */ = {isa = PBXBuildFile; fileRef = 6816DBA72318696600A51400 /* golden_platform_view_opacity_iPhone SE_simulator.png */; };
 		6816DBAD2318696600A51400 /* golden_platform_view_cliprect_iPhone SE_simulator.png in Resources */ = {isa = PBXBuildFile; fileRef = 6816DBA82318696600A51400 /* golden_platform_view_cliprect_iPhone SE_simulator.png */; };
 		6816DBAE2318696600A51400 /* golden_platform_view_cliprrect_iPhone SE_simulator.png in Resources */ = {isa = PBXBuildFile; fileRef = 6816DBA92318696600A51400 /* golden_platform_view_cliprrect_iPhone SE_simulator.png */; };
+		68A5B63423EB71D300BDBCDB /* PlatformViewGestureRecognizerTests.m in Sources */ = {isa = PBXBuildFile; fileRef = 68A5B63323EB71D300BDBCDB /* PlatformViewGestureRecognizerTests.m */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -156,6 +157,7 @@
 		6816DBA72318696600A51400 /* golden_platform_view_opacity_iPhone SE_simulator.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = "golden_platform_view_opacity_iPhone SE_simulator.png"; sourceTree = "<group>"; };
 		6816DBA82318696600A51400 /* golden_platform_view_cliprect_iPhone SE_simulator.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = "golden_platform_view_cliprect_iPhone SE_simulator.png"; sourceTree = "<group>"; };
 		6816DBA92318696600A51400 /* golden_platform_view_cliprrect_iPhone SE_simulator.png */ = {isa = PBXFileReference; lastKnownFileType = image.png; path = "golden_platform_view_cliprrect_iPhone SE_simulator.png"; sourceTree = "<group>"; };
+		68A5B63323EB71D300BDBCDB /* PlatformViewGestureRecognizerTests.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = PlatformViewGestureRecognizerTests.m; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -269,6 +271,7 @@
 				6816DBA02317573300A51400 /* GoldenImage.m */,
 				6816DBA22318358200A51400 /* PlatformViewGoldenTestManager.h */,
 				6816DBA32318358200A51400 /* PlatformViewGoldenTestManager.m */,
+				68A5B63323EB71D300BDBCDB /* PlatformViewGestureRecognizerTests.m */,
 			);
 			path = ScenariosUITests;
 			sourceTree = "<group>";
@@ -458,6 +461,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				68A5B63423EB71D300BDBCDB /* PlatformViewGestureRecognizerTests.m in Sources */,
 				6816DBA12317573300A51400 /* GoldenImage.m in Sources */,
 				6816DB9E231750ED00A51400 /* GoldenPlatformViewTests.m in Sources */,
 				6816DBA42318358200A51400 /* PlatformViewGoldenTestManager.m in Sources */,

testing/scenario_app/ios/Scenarios/Scenarios/AppDelegate.m

@@ -25,7 +25,8 @@ - (BOOL)application:(UIApplication*)application
 
   // This argument is used by the XCUITest for Platform Views so that the app
   // under test will create platform views.
-  // The launchArgsMap should match the one in the `PlatformVieGoldenTestManager`.
+  // If the test is one of the platform view golden tests,
+  // the launchArgsMap should match the one in the `PlatformVieGoldenTestManager`.
   NSDictionary<NSString*, NSString*>* launchArgsMap = @{
     @"--platform-view" : @"platform_view",
     @"--platform-view-multiple" : @"platform_view_multiple",
@@ -37,18 +38,21 @@ - (BOOL)application:(UIApplication*)application
     @"--platform-view-transform" : @"platform_view_transform",
     @"--platform-view-opacity" : @"platform_view_opacity",
     @"--platform-view-rotate" : @"platform_view_rotate",
+    @"--gesture-reject-after-touches-ended" : @"platform_view_gesture_reject_after_touches_ended",
+    @"--gesture-reject-eager" : @"platform_view_gesture_reject_eager",
+    @"--gesture-accept" : @"platform_view_gesture_accept",
   };
-  __block NSString* goldenTestName = nil;
+  __block NSString* platformViewTestName = nil;
   [launchArgsMap
       enumerateKeysAndObjectsUsingBlock:^(NSString* argument, NSString* testName, BOOL* stop) {
         if ([[[NSProcessInfo processInfo] arguments] containsObject:argument]) {
-          goldenTestName = testName;
+          platformViewTestName = testName;
           *stop = YES;
         }
       }];
 
-  if (goldenTestName) {
-    [self readyContextForPlatformViewTests:goldenTestName];
+  if (platformViewTestName) {
+    [self readyContextForPlatformViewTests:platformViewTestName];
   } else if ([[[NSProcessInfo processInfo] arguments] containsObject:@"--screen-before-flutter"]) {
     self.window.rootViewController = [[ScreenBeforeFlutter alloc] initWithEngineRunCompletion:nil];
   } else {
@@ -76,7 +80,13 @@ - (void)readyContextForPlatformViewTests:(NSString*)scenarioIdentifier {
       [[TextPlatformViewFactory alloc] initWithMessenger:flutterViewController.binaryMessenger];
   NSObject<FlutterPluginRegistrar>* registrar =
       [flutterViewController.engine registrarForPlugin:@"scenarios/TextPlatformViewPlugin"];
-  [registrar registerViewFactory:textPlatformViewFactory withId:@"scenarios/textPlatformView"];
+  [registrar registerViewFactory:textPlatformViewFactory
+                                withId:@"scenarios/textPlatformView"
+      gestureRecognizersBlockingPolicy:FlutterPlatformViewGestureRecognizersBlockingPolicyEager];
+  [registrar registerViewFactory:textPlatformViewFactory
+                                withId:@"scenarios/textPlatformView_blockPolicyUntilTouchesEnded"
+      gestureRecognizersBlockingPolicy:
+          FlutterPlatformViewGestureRecognizersBlockingPolicyWaitUntilTouchesEnded];
   self.window.rootViewController = flutterViewController;
 }