Letting ASCellNode and its subclasses handle didScroll

AsyncDisplayKit/ASCellNode+Internal.h

@@ -0,0 +1,15 @@
+//
+//  ASCellNode+Internal.h
+//  Pods
+//
+//  Created by Max Gu on 2/19/16.
+//
+//
+
+#import "ASCellNode.h"
+
+@interface ASCellNode (Internal)
+
+- (void)_visibleNodeDidScroll:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame;
+
+@end

AsyncDisplayKit/ASCellNode.h

@@ -25,15 +25,6 @@ typedef NSUInteger ASCellNodeAnimation;
  */
 - (void)nodeDidRelayout:(ASCellNode *)node sizeChanged:(BOOL)sizeChanged;
 
-@optional
-/**
- * Notifies the delegate that the specified cell node has scrolled
- *
- * @param node: A node informing the delegate about the scroll
- * @param cellFrame: The frame of the cell that has just scrolled
- */
-- (void)visibleNodeDidScroll:(ASCellNode *)node inScrollView:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame;
-
 @end
 
 /**
@@ -120,7 +111,6 @@ typedef NSUInteger ASCellNodeAnimation;
 - (instancetype)initWithViewControllerBlock:(ASDisplayNodeViewControllerBlock)viewControllerBlock didLoadBlock:(ASDisplayNodeDidLoadBlock)didLoadBlock;
 
 - (void)_visibleNodeDidScroll:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame;
-
 @end
 
 

AsyncDisplayKit/ASCellNode.m

@@ -9,7 +9,6 @@
 #import "ASCellNode.h"
 
 #import "ASInternalHelpers.h"
-#import "ASCollectionView.h"
 #import <AsyncDisplayKit/_ASDisplayView.h>
 #import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
 #import <AsyncDisplayKit/ASTextNode.h>
@@ -24,7 +23,6 @@
   UIViewController *_viewController;
   ASDisplayNode *_viewControllerNode;
 }
-@property (nonatomic, assign, readwrite) BOOL shouldMonitorScrollViewDidScroll;
 
 @end
 
@@ -38,9 +36,6 @@
   // Use UITableViewCell defaults
   _selectionStyle = UITableViewCellSelectionStyleDefault;
   self.clipsToBounds = YES;
-  if ([self.layoutDelegate respondsToSelector:@selector(visibleNodeDidScroll:inScrollView:withCellFrame:)]) {
-     self.shouldMonitorScrollViewDidScroll = YES;
-  }
   return self;
 }
 
@@ -60,10 +55,7 @@
     
     [self addSubnode:_viewControllerNode];
   }
-  
+
-  if ([self.layoutDelegate respondsToSelector:@selector(visibleNodeDidScroll:inScrollView:withCellFrame:)]) {
-    self.shouldMonitorScrollViewDidScroll = YES;
-  }
   return self;
 }
 
@@ -143,9 +135,7 @@
 
 - (void)_visibleNodeDidScroll:(UIScrollView *)scrollView withCellFrame:(CGRect)cellFrame
 {
-  if (self.shouldMonitorScrollViewDidScroll) {
+    // To be overriden by subclasses
-    [self.layoutDelegate visibleNodeDidScroll:self inScrollView:scrollView withCellFrame:cellFrame];
-  }
 }
 
 @end

AsyncDisplayKit/ASCollectionView.mm

@@ -9,6 +9,7 @@
 #import "ASAssert.h"
 #import "ASBatchFetching.h"
 #import "ASDelegateProxy.h"
+#import "ASCellNode+Internal.h"
 #import "ASCollectionNode.h"
 #import "ASCollectionDataController.h"
 #import "ASCollectionViewLayoutController.h"
@@ -541,7 +542,9 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   if (cellNode.neverShowPlaceholders) {
     [cellNode recursivelyEnsureDisplaySynchronously:YES];
   }
-  [_cellsForVisibilityUpdates addObject:cell];
+  if (ASSubclassOverridesSelector([ASCellNode class], [cellNode class], @selector(_visibleNodeDidScroll:withCellFrame:))) {
+    [_cellsForVisibilityUpdates addObject:cell];
+  }
 }
 
 - (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath
@@ -553,7 +556,10 @@ 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]) {
+    [_cellsForVisibilityUpdates removeObject:cell];
+  }
+  
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
   if ([_asyncDelegate respondsToSelector:@selector(collectionView:didEndDisplayingNodeForItemAtIndexPath:)]) {
@@ -674,9 +680,8 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
 {
   for (_ASCollectionViewCell *collectionCell in _cellsForVisibilityUpdates) {
     ASCellNode *node = [collectionCell node];
-    if (node.shouldMonitorScrollViewDidScroll) {
+    // Only nodes that respond to the selector are added to _cellsForVisibilityUpdates
-      [node _visibleNodeDidScroll:scrollView withCellFrame: node.frame];
+    [node _visibleNodeDidScroll:scrollView withCellFrame:collectionCell.frame];
-    }
   }
   if (_asyncDelegateImplementsScrollviewDidScroll) {
     [_asyncDelegate scrollViewDidScroll:scrollView];