IGListAdapter support for scrollViewDidEndDecelerating

Summary:
References #842

We use -[UIScrollViewDelegate scrollViewDidEndDecelerating:] delegate callback in the app we are building to hide/show elements when motion has ended.
Closes #899

Differential Revision: D5689239

Pulled By: rnystrom

fbshipit-source-id: ea17fe94ccacc5e4f0a9e085e61f8f77cfcea3b4

CHANGELOG.md

@@ -28,6 +28,7 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 - Added `-[IGListCollectionContext selectItemAtIndex:]` Select an item through IGListCollectionContext like `-[IGListCollectionContext deselectItemAtIndex:]`. [Marvin Nazari](https://github.com/MarvinNazari) (tbd)
 
 - Added horizontal scrolling support to `IGListCollectionViewLayout`. [Peter Edmonston](https://github.com/edmonston) [(#857)](https://github.com/Instagram/IGListKit/pull/857)
+- Added support for scrollViewDidEndDecelerating to `IGListAdapter`. [Phil Larson](https://github.com/plarson) [(#899)](https://github.com/Instagram/IGListKit/pull/899)
 
 - Automatically disable `[UICollectionView isPrefetchingEnabled]` when setting a collection view on an adapter. [Ryan Nystrom](https://github.com/rnystrom) [(#889)](https://github.com/Instagram/IGListKit/pull/889)
 

Source/IGListAdapter.m

@@ -740,6 +740,20 @@ - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL
  }
 }
 
+- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
+ // forward this method to the delegate b/c this implementation will steal the message from the proxy
+ id<UIScrollViewDelegate> scrollViewDelegate = self.scrollViewDelegate;
+ if ([scrollViewDelegate respondsToSelector:@selector(scrollViewDidEndDecelerating:)]) {
+ [scrollViewDelegate scrollViewDidEndDecelerating:scrollView];
+ }
+ NSArray<IGListSectionController *> *visibleSectionControllers = [self visibleSectionControllers];
+ for (IGListSectionController *sectionController in visibleSectionControllers) {
+ id<IGListScrollDelegate> scrollDelegate = [sectionController scrollDelegate];
+ if ([scrollDelegate respondsToSelector:@selector(listAdapter:didEndDeceleratingSectionController:)]) {
+ [scrollDelegate listAdapter:self didEndDeceleratingSectionController:sectionController];
+ }
+ }
+}
 
 #pragma mark - IGListCollectionContext
 

Source/IGListScrollDelegate.h

@@ -46,6 +46,17 @@ NS_SWIFT_NAME(ListScrollDelegate)
  */
 - (void)listAdapter:(IGListAdapter *)listAdapter didEndDraggingSectionController:(IGListSectionController *)sectionController willDecelerate:(BOOL)decelerate;
 
+/**
+ Tells the delegate that the section controller did end decelerating on screen.
+
+ @param listAdapter The list adapter whose collection view ended decelerating.
+ @param sectionController The visible section controller that ended decelerating.
+
+ @note This method is `@optional` until the next breaking-change release.
+ */
+@optional
+- (void)listAdapter:(IGListAdapter *)listAdapter didEndDeceleratingSectionController:(IGListSectionController *)sectionController;
+
 @end
 
 NS_ASSUME_NONNULL_END

Source/IGListStackedSectionController.m

@@ -416,6 +416,15 @@ - (void)listAdapter:(IGListAdapter *)listAdapter didEndDraggingSectionController
  }
 }
 
+- (void)listAdapter:(IGListAdapter *)listAdapter didEndDeceleratingSectionController:(IGListSectionController *)sectionController {
+ for (IGListSectionController *childSectionController in self.sectionControllers) {
+ id<IGListScrollDelegate> scrollDelegate = [childSectionController scrollDelegate];
+ if ([scrollDelegate respondsToSelector:@selector(listAdapter:didEndDeceleratingSectionController:)]) {
+ [scrollDelegate listAdapter:listAdapter didEndDeceleratingSectionController:childSectionController];
+ }
+ }
+}
+
 #pragma mark - IGListWorkingRangeDelegate
 
 - (void)listAdapter:(IGListAdapter *)listAdapter sectionControllerWillEnterWorkingRange:(IGListSectionController *)sectionController {

Source/Internal/IGListAdapterProxy.m

@@ -31,7 +31,8 @@ static BOOL isInterceptedSelector(SEL sel) {
  // UIScrollViewDelegate
  sel == @selector(scrollViewDidScroll:) ||
  sel == @selector(scrollViewWillBeginDragging:) ||
- sel == @selector(scrollViewDidEndDragging:willDecelerate:)
+ sel == @selector(scrollViewDidEndDragging:willDecelerate:) ||
+ sel == @selector(scrollViewDidEndDecelerating:)
  );
 }
 

Tests/IGListAdapterTests.m

@@ -1028,6 +1028,25 @@ - (void)test_whenDidEndDragging_thatScrollViewDelegateReceivesMethod {
  [mockScrollDelegate verify];
 }
 
+- (void)test_whenDidEndDecelerating_thatScrollViewDelegateReceivesMethod {
+ self.dataSource.objects = @[@0, @1, @2];
+ [self.adapter reloadDataWithCompletion:nil];
+
+ id mockCollectionDelegate = [OCMockObject mockForProtocol:@protocol(UICollectionViewDelegate)];
+ id mockScrollDelegate = [OCMockObject mockForProtocol:@protocol(UIScrollViewDelegate)];
+ self.adapter.collectionViewDelegate = mockCollectionDelegate;
+ self.adapter.scrollViewDelegate = mockScrollDelegate;
+
+ [[mockCollectionDelegate reject] scrollViewDidEndDecelerating:self.collectionView];
+ [[mockScrollDelegate expect] scrollViewDidEndDecelerating:self.collectionView];
+
+ // simulates the scrollview delegate telling the adapter that it ended decelerating
+ [self.adapter scrollViewDidEndDecelerating:self.collectionView];
+
+ [mockCollectionDelegate verify];
+ [mockScrollDelegate verify];
+}
+
 - (void)test_whenReloadingObjectsThatDontExist_thatAdapterContinues {
  self.dataSource.objects = @[@0, @1, @2];
  [self.adapter reloadDataWithCompletion:nil];

Tests/IGListStackSectionControllerTests.m

@@ -693,6 +693,34 @@ - (void)test_whenForwardingDidEndDraggingEvent_thatChildSectionControllersReceiv
  [mockScrollDelegate verify];
 }
 
+- (void)test_whenForwardingDidEndDeceleratingEvent_thatChildSectionControllersReceiveEvent {
+ [self setupWithObjects:@[
+ [[IGTestObject alloc] initWithKey:@0 value:@[@1, @2, @3]],
+ [[IGTestObject alloc] initWithKey:@2 value:@[@1, @1]]
+ ]];
+
+ id mockScrollDelegate = [OCMockObject mockForProtocol:@protocol(IGListScrollDelegate)];
+
+ IGListStackedSectionController *stack0 = [self.adapter sectionControllerForObject:self.dataSource.objects[0]];
+ IGListStackedSectionController *stack1 = [self.adapter sectionControllerForObject:self.dataSource.objects[1]];
+
+ [stack0.sectionControllers[0] setScrollDelegate:mockScrollDelegate];
+ [stack0.sectionControllers[1] setScrollDelegate:mockScrollDelegate];
+ [stack0.sectionControllers[2] setScrollDelegate:mockScrollDelegate];
+ [stack1.sectionControllers[0] setScrollDelegate:mockScrollDelegate];
+ [stack1.sectionControllers[1] setScrollDelegate:mockScrollDelegate];
+
+ [[mockScrollDelegate expect] listAdapter:self.adapter didEndDeceleratingSectionController:stack0.sectionControllers[0]];
+ [[mockScrollDelegate expect] listAdapter:self.adapter didEndDeceleratingSectionController:stack0.sectionControllers[1]];
+ [[mockScrollDelegate expect] listAdapter:self.adapter didEndDeceleratingSectionController:stack0.sectionControllers[2]];
+ [[mockScrollDelegate expect] listAdapter:self.adapter didEndDeceleratingSectionController:stack1.sectionControllers[0]];
+ [[mockScrollDelegate expect] listAdapter:self.adapter didEndDeceleratingSectionController:stack1.sectionControllers[1]];
+
+ [self.adapter scrollViewDidEndDecelerating:self.collectionView];
+
+ [mockScrollDelegate verify];
+}
+
 - (void)test_whenUsingSupplementary_withCode_thatSupplementaryViewExists {
  // updater that uses reloadData so we can rebuild all views/sizes
  IGListAdapter *adapter = [[IGListAdapter alloc] initWithUpdater:[IGListReloadDataUpdater new] viewController:nil];