Add an array of scrollviewlisteners in RCTScrollableProtocol

Summary: We are deprecating nativeScrollDelegate property in RCTScrollableProtocol in favor of a scrollListener api. To register/unregister from scroll events use the addScrollListener/removeScrollListener methods

Reviewed By: javache

Differential Revision: D3278218

fbshipit-source-id: 54373cae8e9f8efa7cdbd40c51bcf21d368acf75

React/Views/RCTScrollView.m

@@ -380,6 +380,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
   CGRect _lastClippedToRect;
   uint16_t _coalescingKey;
   NSString *_lastEmittedEventName;
+  NSHashTable *_scrollListeners;
 }
 
 @synthesize nativeScrollDelegate = _nativeScrollDelegate;
@@ -402,6 +403,8 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
     _lastScrollDispatchTime = 0;
     _cachedChildFrames = [NSMutableArray new];
 
+    _scrollListeners = [NSHashTable weakObjectsHashTable];
+
     [self addSubview:_scrollView];
   }
   return self;
@@ -570,8 +573,10 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
 }
 
 #define RCT_FORWARD_SCROLL_EVENT(call) \
-if ([_nativeScrollDelegate respondsToSelector:_cmd]) { \
-  [_nativeScrollDelegate call]; \
+for (NSObject<UIScrollViewDelegate> *scrollViewListener in _scrollListeners) { \
+  if ([scrollViewListener respondsToSelector:_cmd]) { \
+    [scrollViewListener call]; \
+  } \
 }
 
 #define RCT_SCROLL_EVENT_HANDLER(delegateMethod, eventName) \
@@ -584,6 +589,33 @@ if ([_nativeScrollDelegate respondsToSelector:_cmd]) { \
 RCT_SCROLL_EVENT_HANDLER(scrollViewWillBeginDecelerating, onMomentumScrollBegin)
 RCT_SCROLL_EVENT_HANDLER(scrollViewDidZoom, onScroll)
 
+- (void)setNativeScrollDelegate:(NSObject<UIScrollViewDelegate> *)nativeScrollDelegate
+{
+  if (nativeScrollDelegate != _nativeScrollDelegate) {
+    if (_nativeScrollDelegate) {
+      [_scrollListeners removeObject:_nativeScrollDelegate];
+    }
+    if (nativeScrollDelegate) {
+      [_scrollListeners addObject:nativeScrollDelegate];
+    }
+    _nativeScrollDelegate = nativeScrollDelegate;
+  }
+}
+
+- (void)addScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener
+{
+  [_scrollListeners addObject:scrollListener];
+}
+
+- (void)removeScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener
+{
+  if (scrollListener == _nativeScrollDelegate) {
+    [self setNativeScrollDelegate:nil];
+  } else {
+    [_scrollListeners removeObject:scrollListener];
+  }
+}
+
 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
 {
   [_scrollView dockClosestSectionHeader];
@@ -730,7 +762,7 @@ RCT_SCROLL_EVENT_HANDLER(scrollViewDidZoom, onScroll)
   // Fire a final scroll event
   _allowNextScrollNoMatterWhat = YES;
   [self scrollViewDidScroll:scrollView];
-  
+
   // Fire the end deceleration event
   RCT_SEND_SCROLL_EVENT(onMomentumScrollEnd, nil);
   RCT_FORWARD_SCROLL_EVENT(scrollViewDidEndDecelerating:scrollView);
@@ -741,16 +773,19 @@ RCT_SCROLL_EVENT_HANDLER(scrollViewDidZoom, onScroll)
   // Fire a final scroll event
   _allowNextScrollNoMatterWhat = YES;
   [self scrollViewDidScroll:scrollView];
-  
+
   // Fire the end deceleration event
-  RCT_SEND_SCROLL_EVENT(onMomentumScrollEnd, nil); //TODO: shouldn't this be onScrollAnimationEnd? 
+  RCT_SEND_SCROLL_EVENT(onMomentumScrollEnd, nil); //TODO: shouldn't this be onScrollAnimationEnd?
   RCT_FORWARD_SCROLL_EVENT(scrollViewDidEndScrollingAnimation:scrollView);
 }
 
 - (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView
 {
-  if ([_nativeScrollDelegate respondsToSelector:_cmd]) {
-    return [_nativeScrollDelegate scrollViewShouldScrollToTop:scrollView];
+  for (NSObject<UIScrollViewDelegate> *scrollListener in _scrollListeners) {
+    if ([scrollListener respondsToSelector:_cmd] &&
+        ![scrollListener scrollViewShouldScrollToTop:scrollView]) {
+      return NO;
+    }
   }
   return YES;
 }

React/Views/RCTScrollableProtocol.h

@@ -15,11 +15,17 @@
  */
 @protocol RCTScrollableProtocol
 
-@property (nonatomic, weak) NSObject<UIScrollViewDelegate> *nativeScrollDelegate;
+/*
+ * The nativeScrollDelegate property is now deprecated please use the scrollListener API instead
+ */
+@property (nonatomic, weak) NSObject<UIScrollViewDelegate> *nativeScrollDelegate DEPRECATED_ATTRIBUTE;
 @property (nonatomic, readonly) CGSize contentSize;
 
 - (void)scrollToOffset:(CGPoint)offset;
 - (void)scrollToOffset:(CGPoint)offset animated:(BOOL)animated;
 - (void)zoomToRect:(CGRect)rect animated:(BOOL)animated;
 
+- (void)addScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener;
+- (void)removeScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener;
+
 @end