Introduce ASCellNodeDelegate

- Cell node automatically notifies the delegate after a relayout (via -setNeedsLayout) that results in a new size. Confirming to ASCellNodeDelegate; ASTableView and ASCollectionView reload the calling cell upon notifications. These views automatically set themselves as delegate of every node.
- The result is that ASCellNode subclasses don't need to manually notify the containing view. Thus, `-relayoutItemAtIndexPath` and `-relayoutRowAtIndexPath` are removed.
- Kittens example is updated to reflect the change.

AsyncDisplayKit/ASCellNode.h

@@ -8,6 +8,24 @@
 
 #import <AsyncDisplayKit/ASDisplayNode.h>
 
+@class ASCellNode;
+
+typedef NSUInteger ASCellNodeAnimation;
+
+@protocol ASCellNodeDelegate <NSObject>
+
+/**
+ * Notifies the delegate that the specified cell node has done a relayout that results in a new size. 
+ * The notification is done on main thread.
+ *
+ * @param node A node informing the delegate about the relayout.
+ *
+ * @param newSize A new size that is resulted in the relayout.
+ *
+ * @param suggestedAnimation A constant that indicates how the delegate should animate. See UITableViewRowAnimation.
+ */
+- (void)node:(ASCellNode *)node didRelayoutToNewSize:(CGSize)newSize suggestedAnimation:(ASCellNodeAnimation)animation;
+@end
 
 /**
  * Generic cell node.  Subclass this instead of `ASDisplayNode` to use with `ASTableView` and `ASCollectionView`.
@@ -53,6 +71,18 @@
  */
 @property (nonatomic, assign) BOOL highlighted;
 
+/*
+ * A delegate to be notified (on main thread) after a relayout that results in a new size.
+ */
+@property (nonatomic, weak) id<ASCellNodeDelegate> delegate;
+
+/*
+ * A constant that is passed to the delegate to indicate how a relayout is to be animated.
+ * 
+ * @see UITableViewRowAnimation
+ */
+@property (nonatomic, assign) ASCellNodeAnimation relayoutAnimation;
+
 /*
  * ASCellNode must forward touch events in order for UITableView and UICollectionView tap handling to work. Overriding
  * these methods (e.g. for highlighting) requires the super method be called.
@@ -62,6 +92,16 @@
 - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event ASDISPLAYNODE_REQUIRES_SUPER;
 - (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event ASDISPLAYNODE_REQUIRES_SUPER;
 
+/**
+ * Marks the node as needing layout. Convenience for use whether the view / layer is loaded or not. Safe to call from a background thread.
+ *
+ * If this node was measured, calling this method triggers an internal relayout: the calculated layout is invalidated,
+ * and the supernode is notified or (if this node is the root one) a full measurement pass is executed using the old constrained size.
+ *
+ * Note: If the relayout causes a change in size, the delegate will be notified (on main thread) to relayout.
+ */
+- (void)setNeedsLayout;
+
 @end
 
 

AsyncDisplayKit/ASCellNode.m

@@ -8,6 +8,7 @@
 
 #import "ASCellNode.h"
 
+#import "ASInternalHelpers.h"
 #import <AsyncDisplayKit/_ASDisplayView.h>
 #import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
 #import <AsyncDisplayKit/ASTextNode.h>
@@ -27,6 +28,7 @@
   // use UITableViewCell defaults
   _selectionStyle = UITableViewCellSelectionStyleDefault;
   self.clipsToBounds = YES;
+  _relayoutAnimation = UITableViewRowAnimationAutomatic;
 
   return self;
 }
@@ -49,6 +51,21 @@
   ASDisplayNodeAssert(!layerBacked, @"ASCellNode does not support layer-backing.");
 }
 
+- (void)setNeedsLayout
+{
+  ASDisplayNodeAssertThreadAffinity(self);
+  
+  CGSize oldSize = self.calculatedSize;
+  [super setNeedsLayout];
+  CGSize newSize = self.calculatedSize;
+  
+  if (_delegate != nil && !CGSizeEqualToSize(oldSize, newSize)) {
+    ASPerformBlockOnMainThread(^{
+      [_delegate node:self didRelayoutToNewSize:newSize suggestedAnimation:_relayoutAnimation];
+    });
+  }
+}
+
 - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
 {
   ASDisplayNodeAssertMainThread();

AsyncDisplayKit/ASCollectionView.h

@@ -223,16 +223,6 @@
  */
 - (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths;
 
-/**
- * Relayouts the specified item.
- *
- * @param indexPath The index path identifying the item to relayout.
- *
- * @discussion This method must be called from the main thread. The relayout is excuted on main thread.
- * The node of the specified item must be updated to cause layout changes before this method is called.
- */
-- (void)relayoutItemAtIndexPath:(NSIndexPath *)indexPath;
-
 /**
  * Moves the item at a specified location to a destination location.
  *

AsyncDisplayKit/ASCollectionView.mm

@@ -130,7 +130,7 @@ static BOOL _isInterceptedSelector(SEL sel)
 #pragma mark -
 #pragma mark ASCollectionView.
 
-@interface ASCollectionView () <ASRangeControllerDelegate, ASDataControllerSource> {
+@interface ASCollectionView () <ASRangeControllerDelegate, ASDataControllerSource, ASCellNodeDelegate> {
   _ASCollectionViewProxy *_proxyDataSource;
   _ASCollectionViewProxy *_proxyDelegate;
 
@@ -457,14 +457,6 @@ static BOOL _isInterceptedSelector(SEL sel)
   [_dataController reloadRowsAtIndexPaths:indexPaths withAnimationOptions:kASCollectionViewAnimationNone];
 }
 
-- (void)relayoutItemAtIndexPath:(NSIndexPath *)indexPath
-{
-  ASDisplayNodeAssertMainThread();
-  ASCellNode *node = [self nodeForItemAtIndexPath:indexPath];
-  [node setNeedsLayout];
-  [super reloadItemsAtIndexPaths:@[indexPath]];
-}
-
 - (void)moveItemAtIndexPath:(NSIndexPath *)indexPath toIndexPath:(NSIndexPath *)newIndexPath
 {
   ASDisplayNodeAssertMainThread();
@@ -663,6 +655,7 @@ static BOOL _isInterceptedSelector(SEL sel)
 {
   ASCellNode *node = [_asyncDataSource collectionView:self nodeForItemAtIndexPath:indexPath];
   ASDisplayNodeAssert([node isKindOfClass:ASCellNode.class], @"invalid node class, expected ASCellNode");
+  node.delegate = self;
   return node;
 }
 
@@ -906,4 +899,15 @@ static BOOL _isInterceptedSelector(SEL sel)
   }
 }
 
+#pragma mark - ASCellNodeDelegate
+
+- (void)node:(ASCellNode *)node didRelayoutToNewSize:(CGSize)newSize suggestedAnimation:(ASCellNodeAnimation)animation
+{
+  ASDisplayNodeAssertMainThread();
+  NSIndexPath *indexPath = [self indexPathForNode:node];
+  if (indexPath != nil) {
+    [super reloadItemsAtIndexPaths:@[indexPath]];
+  }
+}
+
 @end

AsyncDisplayKit/ASDisplayNode.h

@@ -559,14 +559,6 @@ typedef void (^ASDisplayNodeDidLoadBlock)(ASDisplayNode *node);
  * 
  * If this node was measured, calling this method triggers an internal relayout: the calculated layout is invalidated,
  * and the supernode is notified or (if this node is the root one) a full measurement pass is executed using the old constrained size.
- * 
- * Note: If the relayout causes a change in size of the root node that is attached to a container view, 
- * the container view must be notified to relayout. 
- * For ASTableView and ASCollectionView, instead of calling this method directly, 
- * it is recommended to call -relayoutRowAtIndexPath:withRowAnimation and -relayoutItemAtIndexPath: respectively.
- *
- * @see [ASTableView relayoutRowAtIndexPath:withRowAnimation:]
- * @see [ASCollectionView relayoutItemAtIndexPath:]
  */
 - (void)setNeedsLayout;
 

AsyncDisplayKit/ASTableView.h

@@ -214,18 +214,6 @@
  */
 - (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation;
 
-/**
- * Relayouts the specified row using a given animation effect.
- *
- * @param indexPath The index path identifying the row to relayout.
- *
- * @param animation A constant that indicates how the relayout is to be animated. See UITableViewRowAnimation.
- *
- * @discussion This method must be called from the main thread. The relayout is excuted on main thread. 
- * The node of the specified row must be updated to cause layout changes before this method is called.
- */
-- (void)relayoutRowAtIndexPath:(NSIndexPath *)indexPath withRowAnimation:(UITableViewRowAnimation)animation;
-
 /**
  * Moves the row at a specified location to a destination location.
  *

AsyncDisplayKit/ASTableView.mm

@@ -151,7 +151,7 @@ static BOOL _isInterceptedSelector(SEL sel)
 #pragma mark -
 #pragma mark ASTableView
 
-@interface ASTableView () <ASRangeControllerDelegate, ASDataControllerSource, _ASTableViewCellDelegate> {
+@interface ASTableView () <ASRangeControllerDelegate, ASDataControllerSource, _ASTableViewCellDelegate, ASCellNodeDelegate> {
   _ASTableViewProxy *_proxyDataSource;
   _ASTableViewProxy *_proxyDelegate;
 
@@ -476,14 +476,6 @@ void ASPerformBlockWithoutAnimation(BOOL withoutAnimation, void (^block)()) {
   [_dataController reloadRowsAtIndexPaths:indexPaths withAnimationOptions:animation];
 }
 
-- (void)relayoutRowAtIndexPath:(NSIndexPath *)indexPath withRowAnimation:(UITableViewRowAnimation)animation
-{
-  ASDisplayNodeAssertMainThread();
-  ASCellNode *node = [self nodeForRowAtIndexPath:indexPath];
-  [node setNeedsLayout];
-  [super reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:animation];
-}
-
 - (void)moveRowAtIndexPath:(NSIndexPath *)indexPath toIndexPath:(NSIndexPath *)newIndexPath
 {
   ASDisplayNodeAssertMainThread();
@@ -848,6 +840,7 @@ void ASPerformBlockWithoutAnimation(BOOL withoutAnimation, void (^block)()) {
 {
   ASCellNode *node = [_asyncDataSource tableView:self nodeForRowAtIndexPath:indexPath];
   ASDisplayNodeAssert([node isKindOfClass:ASCellNode.class], @"invalid node class, expected ASCellNode");
+  node.delegate = self;
   return node;
 }
 
@@ -922,4 +915,15 @@ void ASPerformBlockWithoutAnimation(BOOL withoutAnimation, void (^block)()) {
   }
 }
 
+#pragma mark - ASCellNodeDelegate
+
+- (void)node:(ASCellNode *)node didRelayoutToNewSize:(CGSize)newSize suggestedAnimation:(ASCellNodeAnimation)animation
+{
+  ASDisplayNodeAssertMainThread();
+  NSIndexPath *indexPath = [self indexPathForNode:node];
+  if (indexPath != nil) {
+    [super reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:(UITableViewRowAnimation)animation];
+  }
+}
+
 @end

examples/Kittens/Sample/KittenNode.mm

@@ -185,6 +185,7 @@ static const CGFloat kInnerPadding = 10.0f;
 - (void)toggleImageEnlargement
 {
   _isImageEnlarged = !_isImageEnlarged;
+  [self setNeedsLayout];
 }
 
 - (void)toggleNodesSwap

examples/Kittens/Sample/ViewController.m

@@ -121,7 +121,6 @@ static const NSInteger kMaxLitterSize = 100;        // max number of kitten cell
   // Assume only kitten nodes are selectable (see -tableView:shouldHighlightRowAtIndexPath:).
   KittenNode *node = (KittenNode *)[_tableView nodeForRowAtIndexPath:indexPath];
   [node toggleImageEnlargement];
-  [_tableView relayoutRowAtIndexPath:indexPath withRowAnimation:UITableViewRowAnimationAutomatic];
 }
 
 - (ASCellNode *)tableView:(ASTableView *)tableView nodeForRowAtIndexPath:(NSIndexPath *)indexPath