Merge pull request #1292 from nguyenhuy/visibility_improvements

[ASCellNode] Update visibility API to support new event types for initial visibility & invisibility (caused by VC transitions, etc)

AsyncDisplayKit/ASCellNode.h

@@ -14,6 +14,24 @@ NS_ASSUME_NONNULL_BEGIN
 
 typedef NSUInteger ASCellNodeAnimation;
 
+typedef enum : NSUInteger {
+  /** 
+   * Indicates a cell has just became visible 
+   */
+  ASCellNodeVisibilityEventVisible,
+  /**
+   * Its position (determined by scrollView.contentOffset) has changed while at least 1px remains visible.
+   * It is possible that 100% of the cell is visible both before and after and only its position has changed,
+   * or that the position change has resulted in more or less of the cell being visible.
+   * Use CGRectIntersect between cellFrame and scrollView.bounds to get this rectangle
+   */
+  ASCellNodeVisibilityEventVisibleRectChanged,
+  /** 
+   * Indicates a cell is no longer visible 
+   */
+  ASCellNodeVisibilityEventInvisible,
+} ASCellNodeVisibilityEvent;
+
 /**
  * Generic cell node.  Subclass this instead of `ASDisplayNode` to use with `ASTableView` and `ASCollectionView`.
  */
@@ -90,7 +108,7 @@ typedef NSUInteger ASCellNodeAnimation;
  */
 - (instancetype)initWithViewControllerBlock:(ASDisplayNodeViewControllerBlock)viewControllerBlock didLoadBlock:(nullable ASDisplayNodeDidLoadBlock)didLoadBlock;
 
-- (void)visibleNodeDidScroll:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame;
+- (void)cellNodeVisibilityEvent:(ASCellNodeVisibilityEvent)event inScrollView:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame;
 
 @end
 

AsyncDisplayKit/ASCellNode.m

@@ -179,7 +179,9 @@
   [(_ASDisplayView *)self.view __forwardTouchesCancelled:touches withEvent:event];
 }
 
-- (void)visibleNodeDidScroll:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame
+- (void)cellNodeVisibilityEvent:(ASCellNodeVisibilityEvent)event
+                   inScrollView:(UIScrollView *)scrollView
+                  withCellFrame:(CGRect)cellFrame
 {
     // To be overriden by subclasses
 }

AsyncDisplayKit/ASCollectionView.mm

@@ -542,8 +542,11 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   if (cellNode.neverShowPlaceholders) {
     [cellNode recursivelyEnsureDisplaySynchronously:YES];
   }
-  if (ASSubclassOverridesSelector([ASCellNode class], [cellNode class], @selector(visibleNodeDidScroll:withCellFrame:))) {
+  if (ASSubclassOverridesSelector([ASCellNode class], [cellNode class], @selector(cellNodeVisibilityEvent:inScrollView:withCellFrame:))) {
     [_cellsForVisibilityUpdates addObject:cell];
+    [cellNode cellNodeVisibilityEvent:ASCellNodeVisibilityEventVisible
+                         inScrollView:collectionView
+                        withCellFrame:cell.frame];
   }
 }
 
@@ -556,8 +559,14 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
     ASDisplayNodeAssertNotNil(node, @"Expected node associated with removed cell not to be nil.");
     [_asyncDelegate collectionView:self didEndDisplayingNode:node forItemAtIndexPath:indexPath];
   }
-  [_cellsForVisibilityUpdates removeObject:cell];
   
+  if ([_cellsForVisibilityUpdates containsObject:cell]) {
+    ASCellNode *node = ((_ASCollectionViewCell *)cell).node;
+    [node cellNodeVisibilityEvent:ASCellNodeVisibilityEventInvisible
+                     inScrollView:collectionView
+                    withCellFrame:cell.frame];
+    [_cellsForVisibilityUpdates removeObject:cell];
+  }
   
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
@@ -681,9 +690,10 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
 {
   for (_ASCollectionViewCell *collectionCell in _cellsForVisibilityUpdates) {
-    ASCellNode *node = [collectionCell node];
     // Only nodes that respond to the selector are added to _cellsForVisibilityUpdates
-    [node visibleNodeDidScroll:scrollView withCellFrame:collectionCell.frame];
+    [[collectionCell node] cellNodeVisibilityEvent:ASCellNodeVisibilityEventVisibleRectChanged
+                                      inScrollView:scrollView
+                                     withCellFrame:collectionCell.frame];
   }
   if (_asyncDelegateImplementsScrollviewDidScroll) {
     [_asyncDelegate scrollViewDidScroll:scrollView];

AsyncDisplayKit/ASTableView.mm

@@ -597,8 +597,9 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
 - (void)scrollViewDidScroll:(UIScrollView *)scrollView
 {
   for (_ASTableViewCell *tableCell in _cellsForVisibilityUpdates) {
-    ASCellNode *node = [tableCell node];
-    [node visibleNodeDidScroll:scrollView withCellFrame:tableCell.frame];
+    [[tableCell node] cellNodeVisibilityEvent:ASCellNodeVisibilityEventVisibleRectChanged
+                                 inScrollView:scrollView
+                                withCellFrame:tableCell.frame];
   }
   if (_asyncDelegateImplementsScrollviewDidScroll) {
     [_asyncDelegate scrollViewDidScroll:scrollView];
@@ -617,8 +618,11 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
 
   ASCellNode *cellNode = [cell node];
 
-  if (ASSubclassOverridesSelector([ASCellNode class], [cellNode class], @selector(visibleNodeDidScroll:withCellFrame:))) {
+  if (ASSubclassOverridesSelector([ASCellNode class], [cellNode class], @selector(cellNodeVisibilityEvent:inScrollView:withCellFrame:))) {
     [_cellsForVisibilityUpdates addObject:cell];
+    [cellNode cellNodeVisibilityEvent:ASCellNodeVisibilityEventVisible
+                         inScrollView:tableView
+                        withCellFrame:cell.frame];
   }
   if (cellNode.neverShowPlaceholders) {
     [cellNode recursivelyEnsureDisplaySynchronously:YES];
@@ -639,7 +643,13 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
     [_asyncDelegate tableView:self didEndDisplayingNode:node forRowAtIndexPath:indexPath];
   }
 
+  if ([_cellsForVisibilityUpdates containsObject:cell]) {
     [_cellsForVisibilityUpdates removeObject:cell];
+    ASCellNode *node = ((_ASTableViewCell *)cell).node;
+    [node cellNodeVisibilityEvent:ASCellNodeVisibilityEventInvisible
+                     inScrollView:tableView
+                    withCellFrame:cell.frame];
+  }
 
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"