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Add `onScrollToTop` to ScrollView for iOS (#21204) 

Summary:
This PR exposes the `onScrollToTop` event on iOS using the same event-forwarding infrastructure as other ScrollView events. (As such, its `nativeEvent` object reflects the same fields as other ScrollView events.)

Motivation:
----------

If your app is only interested in knowing the position of a ScrollView after a scroll has completed, it can use `onScrollEndDrag` and `onMomentumScrollEnd` to inspect the `contentOffset` after a drag-initiated scroll has finished. (This is much less expensive than observing the `onScroll` event if you only want to know the end position.) However, neither of these `End` events fire if the ScrollView is scrolled to the top by tapping the status bar.

By exposing `onScrollToTop`, it is now possible for an app to cheaply know when such a scroll has completed.
Pull Request resolved: https://github.com/facebook/react-native/pull/21204

Differential Revision: D9943618

Pulled By: hramos

fbshipit-source-id: ac5ee42b7f12d94655ffda617f8f811138da7f6f
This commit is contained in:
James Reggio 2018-09-19 11:15:54 -07:00 committed by Facebook Github Bot
parent 58fe324163
commit 9733b92f3d
4 changed files with 8 additions and 0 deletions
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5
Libraries/Components/ScrollView/ScrollView.js
View File

@ -217,6 +217,11 @@ type IOSProps = $ReadOnly<{|
* @platform ios
*/
scrollsToTop?: ?boolean,
/**
* Fires when the scroll view scrolls to top after the status bar has been tapped
* @platform ios
*/
onScrollToTop?: ?Function,
/**
* When true, shows a horizontal scroll indicator.
* The default value is true.

1
React/Views/ScrollView/RCTScrollView.h
View File

@ -55,6 +55,7 @@
// need to be coalesced before sending, for performance reasons.
@property (nonatomic, copy) RCTDirectEventBlock onScrollBeginDrag;
@property (nonatomic, copy) RCTDirectEventBlock onScroll;
@property (nonatomic, copy) RCTDirectEventBlock onScrollToTop;
@property (nonatomic, copy) RCTDirectEventBlock onScrollEndDrag;
@property (nonatomic, copy) RCTDirectEventBlock onMomentumScrollBegin;
@property (nonatomic, copy) RCTDirectEventBlock onMomentumScrollEnd;

1
React/Views/ScrollView/RCTScrollView.m
View File

@ -648,6 +648,7 @@ for (NSObject<UIScrollViewDelegate> *scrollViewListener in _scrollListeners) { \
RCT_SCROLL_EVENT_HANDLER(scrollViewWillBeginDecelerating, onMomentumScrollBegin)
RCT_SCROLL_EVENT_HANDLER(scrollViewDidZoom, onScroll)
RCT_SCROLL_EVENT_HANDLER(scrollViewDidScrollToTop, onScrollToTop)
- (void)addScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener
{

1
React/Views/ScrollView/RCTScrollViewManager.m
View File

@ -88,6 +88,7 @@ RCT_EXPORT_VIEW_PROPERTY(snapToAlignment, NSString)
RCT_REMAP_VIEW_PROPERTY(contentOffset, scrollView.contentOffset, CGPoint)
RCT_EXPORT_VIEW_PROPERTY(onScrollBeginDrag, RCTDirectEventBlock)
RCT_EXPORT_VIEW_PROPERTY(onScroll, RCTDirectEventBlock)
RCT_EXPORT_VIEW_PROPERTY(onScrollToTop, RCTDirectEventBlock)
RCT_EXPORT_VIEW_PROPERTY(onScrollEndDrag, RCTDirectEventBlock)
RCT_EXPORT_VIEW_PROPERTY(onMomentumScrollBegin, RCTDirectEventBlock)
RCT_EXPORT_VIEW_PROPERTY(onMomentumScrollEnd, RCTDirectEventBlock)