Allow bound views to listen to handler updates and state changes

Author: j-piasecki

packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.h

@@ -11,5 +11,25 @@
 @interface RNDummyGestureRecognizer : UIGestureRecognizer
 @end
 
+/*
+ * Views bound to a `RNNativeViewGestureHandler` may conform to this protocol to
+ * be notified about the handler's updates and state changes.
+ */
+@protocol RNGHNativeViewHandlerStateObserver <NSObject>
+
+/*
+ * Called when the handler dispatches a new update event in the ACTIVE state.
+ */
+- (void)onHandlerUpdate:(nonnull RNGestureHandlerEventExtraData *)extraData;
+
+/*
+ * Called when the handler moves to a new state.
+ */
+- (void)onHandlerStateChange:(RNGestureHandlerState)newState
+                   prevState:(RNGestureHandlerState)prevState
+                   extraData:(nonnull RNGestureHandlerEventExtraData *)extraData;
+
+@end
+
 @interface RNNativeViewGestureHandler : RNGestureHandler
 @end

packages/react-native-gesture-handler/apple/Handlers/RNNativeViewHandler.mm

@@ -116,6 +116,11 @@ @implementation RNNativeViewGestureHandler {
   BOOL _yieldsToContinuousGestures;
   BOOL _delaysChildPressedState;
   RNGestureHandlerEventExtraData *_lastActiveExtraData;
+
+  // For UIControl-based views the recognizer is never attached, so
+  // `recognizer.view` cannot be used to retrieve the bound view.
+  __weak RNGHUIView *_boundView;
+  __weak id<RNGHNativeViewHandlerStateObserver> _stateObserver;
 }
 
 - (instancetype)initWithTag:(NSNumber *)tag
@@ -146,9 +151,54 @@ - (void)updateConfig:(NSDictionary *)config
 #endif
 }
 
+- (void)bindToView:(RNGHUIView *)view
+{
+  _boundView = view;
+
+  if ([view conformsToProtocol:@protocol(RNGHNativeViewHandlerStateObserver)]) {
+    _stateObserver = (id<RNGHNativeViewHandlerStateObserver>)view;
+  }
+
+#if !TARGET_OS_OSX
+  [self bindToUIKitView:view];
+#else
+  [super bindToView:view];
+#endif
+}
+
+- (void)unbindFromView
+{
+#if !TARGET_OS_OSX
+  if ([_boundView isKindOfClass:[UIControl class]]) {
+    [(UIControl *)_boundView removeTarget:self action:NULL forControlEvents:UIControlEventAllEvents];
+  }
+
+  // Restore the React Native's overriden behavor for not delaying content touches
+  UIScrollView *scrollView = [self retrieveScrollView:_boundView];
+  scrollView.delaysContentTouches = NO;
+#endif
+
+  _boundView = nil;
+  _stateObserver = nil;
+
+  [super unbindFromView];
+}
+
+- (void)dispatchStateChange:(RNGestureHandlerState)newState
+                  prevState:(RNGestureHandlerState)prevState
+                  extraData:(RNGestureHandlerEventExtraData *)extraData
+{
+  [_stateObserver onHandlerStateChange:newState prevState:prevState extraData:extraData];
+}
+
+- (void)dispatchHandlerUpdate:(RNGestureHandlerEventExtraData *)extraData
+{
+  [_stateObserver onHandlerUpdate:extraData];
+}
+
 #if !TARGET_OS_OSX
 
-- (void)bindToView:(UIView *)view
+- (void)bindToUIKitView:(UIView *)view
 {
   // For UIControl based views (UIButton, UISwitch) we provide special handling that would allow
   // for properties like `disallowInterruption` to work.
@@ -196,21 +246,6 @@ - (void)bindToView:(UIView *)view
   scrollView.delaysContentTouches = _delaysChildPressedState;
 }
 
-- (void)unbindFromView
-{
-  UIView *view = self.recognizer.view;
-
-  if ([view isKindOfClass:[UIControl class]]) {
-    [(UIControl *)view removeTarget:self action:NULL forControlEvents:UIControlEventAllEvents];
-  }
-
-  // Restore the React Native's overriden behavor for not delaying content touches
-  UIScrollView *scrollView = [self retrieveScrollView:view];
-  scrollView.delaysContentTouches = NO;
-
-  [super unbindFromView];
-}
-
 - (RNGestureHandlerEventExtraData *)extraDataForView:(UIView *)sender
                                                event:(UIEvent *)event
                                        pointerInside:(BOOL)pointerInside

packages/react-native-gesture-handler/apple/RNGestureHandler.h

@@ -125,6 +125,21 @@
 
 - (void)stopActivationBlocker;
 - (void)reset;
+
+/*
+ * Called after a state-change event has been dispatched. No-op by default, may be
+ * overridden by subclasses to observe the state flow regardless of the action type.
+ */
+- (void)dispatchStateChange:(RNGestureHandlerState)newState
+                  prevState:(RNGestureHandlerState)prevState
+                  extraData:(nonnull RNGestureHandlerEventExtraData *)extraData;
+
+/*
+ * Called after an update event has been dispatched in the ACTIVE state. No-op by
+ * default, may be overridden by subclasses.
+ */
+- (void)dispatchHandlerUpdate:(nonnull RNGestureHandlerEventExtraData *)extraData;
+
 - (void)sendEventsInState:(RNGestureHandlerState)state
            forViewWithTag:(nonnull NSNumber *)reactTag
             withExtraData:(nonnull RNGestureHandlerEventExtraData *)extraData;

packages/react-native-gesture-handler/apple/RNGestureHandler.mm

@@ -534,21 +534,25 @@ - (void)sendEventsInState:(RNGestureHandlerState)state
         state == RNGestureHandlerStateEnd && _lastState != RNGestureHandlerStateActive && !fromManualStateChange &&
         !_manualActivation) {
       // Otherwise send activate state change event to preserve correct gesture flow
+      RNGestureHandlerState prevSynthesizedState = _lastState;
       id event = [[RNGestureHandlerStateChange alloc] initWithReactTag:reactTag
                                                             handlerTag:_tag
                                                                  state:RNGestureHandlerStateActive
                                                              prevState:_lastState
                                                              extraData:extraData];
       [self sendEvent:event];
       _lastState = RNGestureHandlerStateActive;
+      [self dispatchStateChange:RNGestureHandlerStateActive prevState:prevSynthesizedState extraData:extraData];
     }
+    RNGestureHandlerState prevState = _lastState;
     id stateEvent = [[RNGestureHandlerStateChange alloc] initWithReactTag:reactTag
                                                                handlerTag:_tag
                                                                     state:state
                                                                 prevState:_lastState
                                                                 extraData:extraData];
     [self sendEvent:stateEvent];
     _lastState = state;
+    [self dispatchStateChange:state prevState:prevState extraData:extraData];
   }
 
   if (state == RNGestureHandlerStateActive) {
@@ -559,9 +563,22 @@ - (void)sendEventsInState:(RNGestureHandlerState)state
                                                      forHandlerType:[self eventHandlerType]
                                                       coalescingKey:self->_eventCoalescingKey];
     [self sendEvent:touchEvent];
+    [self dispatchHandlerUpdate:extraData];
   }
 }
 
+- (void)dispatchStateChange:(RNGestureHandlerState)newState
+                  prevState:(RNGestureHandlerState)prevState
+                  extraData:(RNGestureHandlerEventExtraData *)extraData
+{
+  // no-op
+}
+
+- (void)dispatchHandlerUpdate:(RNGestureHandlerEventExtraData *)extraData
+{
+  // no-op
+}
+
 - (RNGHUIView *)findViewForEvents
 {
   return [self usesNativeOrVirtualDetector] ? self.hostDetectorView : self.recognizer.view;