API for cancelling RCTTouchHandler

Reviewed By: spicyj

Differential Revision: D2846573

fb-gh-sync-id: 652864c773d03c24f0d68dd8335401eb052fc1bf

React/Base/RCTRootView.h

@@ -123,6 +123,25 @@ extern NSString *const RCTContentDidAppearNotification;
  */
 @property (nonatomic, strong) UIView *loadingView;
 
+/**
+ * Calling this will result in emitting a "touches cancelled" event to js,
+ * which effectively cancels all js "gesture recognizers" such as as touchable
+ * (unless they explicitely ignore cancellation events, but noone should do that).
+ *
+ * This API is exposed for integration purposes where you embed RN rootView
+ * in a native view with a native gesture recognizer,
+ * whose activation should prevent any in-flight js "gesture recognizer" from activating.
+ *
+ * An example would be RN rootView embedded in an UIScrollView.
+ * When you touch down on a touchable component and drag your finger up,
+ * you don't want any touch to be registered as soon as the UIScrollView starts scrolling.
+ *
+ * Note that this doesn't help with tapping on a touchable element that is being scrolled,
+ * unless you can call cancelTouches exactly between "touches began" and "touches ended" events.
+ * This is a reason why this API may be soon removed in favor of a better solution.
+ */
+- (void)cancelTouches;
+
 /**
  * Timings for hiding the loading view after the content has loaded. Both of
  * these values default to 0.25 seconds.

React/Base/RCTRootView.m

@@ -38,6 +38,8 @@ NSString *const RCTContentDidAppearNotification = @"RCTContentDidAppearNotificat
 
 @property (nonatomic, readonly) BOOL contentHasAppeared;
 
+@property (nonatomic, readonly, strong) RCTTouchHandler *touchHandler;
+
 - (instancetype)initWithFrame:(CGRect)frame bridge:(RCTBridge *)bridge NS_DESIGNATED_INITIALIZER;
 
 @end
@@ -257,6 +259,11 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
   [_contentView invalidate];
 }
 
+- (void)cancelTouches
+{
+  [[_contentView touchHandler] cancel];
+}
+
 @end
 
 @implementation RCTUIManager (RCTRootView)
@@ -273,7 +280,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
 @implementation RCTRootContentView
 {
   __weak RCTBridge *_bridge;
-  RCTTouchHandler *_touchHandler;
   UIColor *_backgroundColor;
 }
 
@@ -335,7 +341,8 @@ RCT_NOT_IMPLEMENTED(-(instancetype)initWithCoder:(nonnull NSCoder *)aDecoder)
    * the react tag is assigned every time we load new content.
    */
   self.reactTag = [_bridge.uiManager allocateRootTag];
-  [self addGestureRecognizer:[[RCTTouchHandler alloc] initWithBridge:_bridge]];
+  _touchHandler = [[RCTTouchHandler alloc] initWithBridge:_bridge];
+  [self addGestureRecognizer:_touchHandler];
   [_bridge.uiManager registerRootView:self];
 }
 

React/Base/RCTTouchHandler.h

@@ -16,5 +16,6 @@
 @interface RCTTouchHandler : UIGestureRecognizer
 
 - (instancetype)initWithBridge:(RCTBridge *)bridge NS_DESIGNATED_INITIALIZER;
+- (void)cancel;
 
 @end

React/Base/RCTTouchHandler.m

@@ -311,4 +311,10 @@ static BOOL RCTAnyTouchesChanged(NSSet<UITouch *> *touches)
   _dispatchedInitialTouches = NO;
 }
 
+- (void)cancel
+{
+  self.enabled = NO;
+  self.enabled = YES;
+}
+
 @end