From 1fba62da0eff538794c17fc20f9d64c96944b071 Mon Sep 17 00:00:00 2001
From: Max Gu <maxgu@pinterest.com>
Date: Thu, 24 Mar 2016 14:50:08 -0700
Subject: [PATCH] Adding scrollViewWillBeginDragging and
 scrollViewDidEndDragging callbac to ASCellNode instances

---
 AsyncDisplayKit/ASCellNode.h              |  8 ++++++
 AsyncDisplayKit/ASCollectionView.mm       | 30 +++++++++++++++++++++++
 AsyncDisplayKit/Details/ASDelegateProxy.m |  8 ++++++
 3 files changed, 46 insertions(+)

diff --git a/AsyncDisplayKit/ASCellNode.h b/AsyncDisplayKit/ASCellNode.h
index 6e11c859..6f3dc043 100644
--- a/AsyncDisplayKit/ASCellNode.h
+++ b/AsyncDisplayKit/ASCellNode.h
@@ -30,6 +30,14 @@ typedef NS_ENUM(NSUInteger, ASCellNodeVisibilityEvent) {
    * Indicates a cell is no longer visible
    */
   ASCellNodeVisibilityEventInvisible,
+  /**
+   * Indicates user has started dragging the visible cell
+   */
+  ASCellNodeVisibilityEventWillBeginDragging,
+  /**
+   * Indicates user has ended dragging the visible cell
+   */
+  ASCellNodeVisibilityEventDidEndDragging,
 };
 
 /**
diff --git a/AsyncDisplayKit/ASCollectionView.mm b/AsyncDisplayKit/ASCollectionView.mm
index ae1f5792..ab815e50 100644
--- a/AsyncDisplayKit/ASCollectionView.mm
+++ b/AsyncDisplayKit/ASCollectionView.mm
@@ -107,6 +107,8 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   
   BOOL _asyncDataFetchingEnabled;
   BOOL _asyncDelegateImplementsScrollviewDidScroll;
+  BOOL _asyncDelegateImplementsWillBeginDragging;
+  BOOL _asyncDelegateImplementsDidEndDragging;
   BOOL _asyncDataSourceImplementsConstrainedSizeForNode;
   BOOL _asyncDataSourceImplementsNodeBlockForItemAtIndexPath;
   _ASCollectionViewNodeSizeInvalidationContext *_queuedNodeSizeInvalidationContext; // Main thread only
@@ -364,10 +366,14 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
     _asyncDelegate = nil;
     _proxyDelegate = _isDeallocating ? nil : [[ASCollectionViewProxy alloc] initWithTarget:nil interceptor:self];
     _asyncDelegateImplementsScrollviewDidScroll = NO;
+    _asyncDelegateImplementsWillBeginDragging = NO;
+    _asyncDelegateImplementsDidEndDragging = NO;
   } else {
     _asyncDelegate = asyncDelegate;
     _proxyDelegate = [[ASCollectionViewProxy alloc] initWithTarget:_asyncDelegate interceptor:self];
     _asyncDelegateImplementsScrollviewDidScroll = ([_asyncDelegate respondsToSelector:@selector(scrollViewDidScroll:)] ? 1 : 0);
+    _asyncDelegateImplementsWillBeginDragging = ([_asyncDelegate respondsToSelector:@selector(scrollViewWillBeginDragging:)] ? 1 : 0);
+    _asyncDelegateImplementsDidEndDragging = ([_asyncDelegate respondsToSelector:@selector(scrollViewDidEndDragging:willDecelerate:)] ? 1 : 0);
   }
 
   super.delegate = (id<UICollectionViewDelegate>)_proxyDelegate;
@@ -738,6 +744,30 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   }
 }
 
+- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
+{
+  for (_ASCollectionViewCell *collectionCell in _cellsForVisibilityUpdates) {
+    [[collectionCell node] cellNodeVisibilityEvent:ASCellNodeVisibilityEventWillBeginDragging
+                                      inScrollView:scrollView
+                                     withCellFrame:collectionCell.frame];
+    }
+    if (_asyncDelegateImplementsWillBeginDragging) {
+      [_asyncDelegate scrollViewWillBeginDragging:scrollView];
+    }
+}
+
+- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
+{
+  for (_ASCollectionViewCell *collectionCell in _cellsForVisibilityUpdates) {
+    [[collectionCell node] cellNodeVisibilityEvent:ASCellNodeVisibilityEventDidEndDragging
+                                      inScrollView:scrollView
+                                     withCellFrame:collectionCell.frame];
+    }
+    if (_asyncDelegateImplementsDidEndDragging) {
+        [_asyncDelegate scrollViewDidEndDragging:scrollView willDecelerate:decelerate];
+    }
+}
+
 - (BOOL)shouldBatchFetch
 {
   // if the delegate does not respond to this method, there is no point in starting to fetch
diff --git a/AsyncDisplayKit/Details/ASDelegateProxy.m b/AsyncDisplayKit/Details/ASDelegateProxy.m
index 3034a83d..032de4c6 100644
--- a/AsyncDisplayKit/Details/ASDelegateProxy.m
+++ b/AsyncDisplayKit/Details/ASDelegateProxy.m
@@ -27,6 +27,10 @@
           // used for ASCellNode visibility
           selector == @selector(scrollViewDidScroll:) ||
           
+          // used for ASCellNode user interaction
+          selector == @selector(scrollViewWillBeginDragging:) ||
+          selector == @selector(scrollViewDidEndDragging:willDecelerate:) ||
+
           // used for ASRangeController visibility updates
           selector == @selector(tableView:willDisplayCell:forRowAtIndexPath:) ||
           selector == @selector(tableView:didEndDisplayingCell:forRowAtIndexPath:) ||
@@ -62,6 +66,10 @@
           // used for ASCellNode visibility
           selector == @selector(scrollViewDidScroll:) ||
           
+          // used for ASCellNode user interaction
+          selector == @selector(scrollViewWillBeginDragging:) ||
+          selector == @selector(scrollViewDidEndDragging:willDecelerate:) ||
+          
           // intercepted due to not being supported by ASCollectionView (prevent bugs caused by usage)
           selector == @selector(collectionView:canMoveItemAtIndexPath:) ||
           selector == @selector(collectionView:moveItemAtIndexPath:toIndexPath:) ||