Fabric: Support for <ScrollView scrollEventThrottle={...}> on iOS

Summary: This diff adds support from `ScrollView::scrollEventThrottle` property on iOS. Reviewed By: JoshuaGross Differential Revision: D17000397 fbshipit-source-id: 93f23919a6a2588000c0eeca869171d1036348b6
facebook · Aug 27, 2019 · 59c3d05 · 59c3d05
1 parent be2a252
commit 59c3d05
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Showing 2 changed files with 52 additions and 17 deletions.
diff --git a/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm b/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm
@@ -22,13 +22,13 @@
 
 @interface RCTScrollViewComponentView () <UIScrollViewDelegate>
 
-@property (nonatomic, assign) CGFloat scrollEventThrottle;
-
 @end
 
 @implementation RCTScrollViewComponentView {
   ScrollViewShadowNode::ConcreteState::Shared _state;
   CGSize _contentSize;
+  NSTimeInterval _lastScrollEventDispatchTime;
+  NSTimeInterval _scrollEventThrottle;
 }
 
 + (RCTScrollViewComponentView *_Nullable)findScrollViewComponentViewForView:(UIView *)view
@@ -59,6 +59,8 @@ - (instancetype)initWithFrame:(CGRect)frame
     }];
 
     [_scrollViewDelegateSplitter addDelegate:self];
+
+    _scrollEventThrottle = INFINITY;
   }
 
   return self;
@@ -107,7 +109,17 @@ - (void)updateProps:(Props::Shared const &)props oldProps:(Props::Shared const &
   MAP_SCROLL_VIEW_PROP(scrollsToTop);
   MAP_SCROLL_VIEW_PROP(showsHorizontalScrollIndicator);
   MAP_SCROLL_VIEW_PROP(showsVerticalScrollIndicator);
-  MAP_VIEW_PROP(scrollEventThrottle);
+
+  if (oldScrollViewProps.scrollEventThrottle != newScrollViewProps.scrollEventThrottle) {
+    // Zero means "send value only once per significant logical event".
+    // Prop value is in milliseconds.
+    // iOS implementation uses `NSTimeInterval` (in seconds).
+    // 16 ms is the minimum allowed value.
+    _scrollEventThrottle = newScrollViewProps.scrollEventThrottle <= 0
+        ? INFINITY
+        : std::max(newScrollViewProps.scrollEventThrottle / 1000.0, 1.0 / 60.0);
+  }
+
   MAP_SCROLL_VIEW_PROP(zoomScale);
 
   if (oldScrollViewProps.contentInset != newScrollViewProps.contentInset) {
@@ -184,87 +196,108 @@ - (void)scrollViewDidScroll:(UIScrollView *)scrollView
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScroll([self _scrollViewMetrics]);
+  NSTimeInterval now = CACurrentMediaTime();
+  if ((_lastScrollEventDispatchTime == 0) || (now - _lastScrollEventDispatchTime > _scrollEventThrottle)) {
+    _lastScrollEventDispatchTime = now;
+    std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onScroll([self _scrollViewMetrics]);
+  }
 }
 
 - (void)scrollViewDidZoom:(UIScrollView *)scrollView
 {
-  if (!_eventEmitter) {
-    return;
-  }
-
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScroll([self _scrollViewMetrics]);
+  [self scrollViewDidScroll:scrollView];
 }
 
 - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScrollBeginDrag([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onScrollBeginDrag([self _scrollViewMetrics]);
 }
 
 - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
                      withVelocity:(CGPoint)velocity
               targetContentOffset:(inout CGPoint *)targetContentOffset
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScrollEndDrag([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onScrollEndDrag([self _scrollViewMetrics]);
 }
 
 - (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)
       ->onMomentumScrollBegin([self _scrollViewMetrics]);
 }
 
 - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onMomentumScrollEnd([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onMomentumScrollEnd([self _scrollViewMetrics]);
   [self _updateStateWithContentOffset];
 }
 
 - (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onMomentumScrollEnd([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onMomentumScrollEnd([self _scrollViewMetrics]);
   [self _updateStateWithContentOffset];
 }
 
 - (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(nullable UIView *)view
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScrollBeginDrag([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onScrollBeginDrag([self _scrollViewMetrics]);
 }
 
 - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(nullable UIView *)view atScale:(CGFloat)scale
 {
+  [self _forceDispatchNextScrollEvent];
+
   if (!_eventEmitter) {
     return;
   }
 
-  std::static_pointer_cast<const ScrollViewEventEmitter>(_eventEmitter)->onScrollEndDrag([self _scrollViewMetrics]);
+  std::static_pointer_cast<ScrollViewEventEmitter const>(_eventEmitter)->onScrollEndDrag([self _scrollViewMetrics]);
   [self _updateStateWithContentOffset];
 }
 
+#pragma mark - UIScrollViewDelegate
+
+- (void)_forceDispatchNextScrollEvent
+{
+  _lastScrollEventDispatchTime = 0;
+}
+
 @end
 
 @implementation RCTScrollViewComponentView (ScrollableProtocol)
@@ -276,11 +309,13 @@ - (CGSize)contentSize
 
 - (void)scrollToOffset:(CGPoint)offset
 {
+  [self _forceDispatchNextScrollEvent];
   [self scrollToOffset:offset animated:YES];
 }
 
 - (void)scrollToOffset:(CGPoint)offset animated:(BOOL)animated
 {
+  [self _forceDispatchNextScrollEvent];
   [self.scrollView setContentOffset:offset animated:animated];
 }
 

diff --git a/ReactCommon/fabric/components/scrollview/ScrollViewProps.h b/ReactCommon/fabric/components/scrollview/ScrollViewProps.h
@@ -40,7 +40,7 @@ class ScrollViewProps final : public ViewProps {
   const bool scrollsToTop{true};
   const bool showsHorizontalScrollIndicator{true};
   const bool showsVerticalScrollIndicator{true};
-  const Float scrollEventThrottle{};
+  const int scrollEventThrottle{};
   const Float zoomScale{1.0};
   const EdgeInsets contentInset{};
   const EdgeInsets scrollIndicatorInsets{};