Add extension points for global node behaviors, potentially replacing…

… interface state delegates (#1229)

* Add extension points for global node behaviors via categories and a public ivar

* Update documentation on context ivar

Source/ASDisplayNode+Beta.h

@@ -143,7 +143,14 @@ typedef struct {
  * this hook could be called up to 1 + (pJPEGcount * pJPEGrenderCount) times. The render count depends on how many times the downloader calls the
  * progressImage block.
  */
-- (void)hierarchyDisplayDidFinish;
+AS_CATEGORY_IMPLEMENTABLE
+- (void)hierarchyDisplayDidFinish NS_REQUIRES_SUPER;
+
+/**
+ * Only called on the root during yoga layout.
+ */
+AS_CATEGORY_IMPLEMENTABLE
+- (void)willCalculateLayout:(ASSizeRange)constrainedSize NS_REQUIRES_SUPER;
 
 /**
  * Only ASLayoutRangeModeVisibleOnly or ASLayoutRangeModeLowMemory are recommended.  Default is ASLayoutRangeModeVisibleOnly,

Source/ASDisplayNode+Subclasses.h

@@ -69,8 +69,22 @@ NS_ASSUME_NONNULL_BEGIN
  *
  * @discussion This is the best time to add gesture recognizers to the view.
  */
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didLoad ASDISPLAYNODE_REQUIRES_SUPER;
 
+/**
+ * An empty method that you can implement in a category to add global
+ * node initialization behavior. This method will be called by [ASDisplayNode init].
+ */
+AS_CATEGORY_IMPLEMENTABLE
+- (void)baseDidInit;
+
+/**
+ * An empty method that you can implement in a category to add global
+ * node deallocation behavior. This method will be called by [ASDisplayNode dealloc].
+ */
+AS_CATEGORY_IMPLEMENTABLE
+- (void)baseWillDealloc;
 
 #pragma mark - Layout
 /** @name Layout */
@@ -88,6 +102,7 @@ NS_ASSUME_NONNULL_BEGIN
  * @discussion Gives a chance for subclasses to perform actions after the subclass and superclass have finished laying
  * out.
  */
+AS_CATEGORY_IMPLEMENTABLE
 - (void)layoutDidFinish ASDISPLAYNODE_REQUIRES_SUPER;
 
 /**
@@ -96,6 +111,7 @@ NS_ASSUME_NONNULL_BEGIN
  * @discussion When the .calculatedLayout property is set to a new ASLayout (directly from -calculateLayoutThatFits: or
  * calculated via use of -layoutSpecThatFits:), subclasses may inspect it here.
  */
+AS_CATEGORY_IMPLEMENTABLE
 - (void)calculatedLayoutDidChange ASDISPLAYNODE_REQUIRES_SUPER;
 
 
@@ -162,15 +178,25 @@ NS_ASSUME_NONNULL_BEGIN
   * For descriptions, see <ASInterfaceStateDelegate> definition.
   */
 
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didEnterVisibleState ASDISPLAYNODE_REQUIRES_SUPER;
+
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didExitVisibleState  ASDISPLAYNODE_REQUIRES_SUPER;
 
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didEnterDisplayState ASDISPLAYNODE_REQUIRES_SUPER;
+
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didExitDisplayState  ASDISPLAYNODE_REQUIRES_SUPER;
 
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didEnterPreloadState ASDISPLAYNODE_REQUIRES_SUPER;
+
+AS_CATEGORY_IMPLEMENTABLE
 - (void)didExitPreloadState  ASDISPLAYNODE_REQUIRES_SUPER;
 
+AS_CATEGORY_IMPLEMENTABLE
 - (void)interfaceStateDidChange:(ASInterfaceState)newState
                       fromState:(ASInterfaceState)oldState ASDISPLAYNODE_REQUIRES_SUPER;
 
@@ -179,6 +205,7 @@ NS_ASSUME_NONNULL_BEGIN
  *
  * @discussion Subclasses can override this method to react to a trait collection change.
  */
+AS_CATEGORY_IMPLEMENTABLE
 - (void)asyncTraitCollectionDidChange;
 
 #pragma mark - Drawing

Source/ASDisplayNode+Yoga.mm

@@ -338,6 +338,7 @@ - (void)calculateLayoutFromYogaRoot:(ASSizeRange)rootConstrainedSize
     return;
   }
 
+  [self willCalculateLayout:rootConstrainedSize];
   [self enumerateInterfaceStateDelegates:^(id<ASInterfaceStateDelegate>  _Nonnull delegate) {
     if ([delegate respondsToSelector:@selector(nodeWillCalculateLayout:)]) {
       [delegate nodeWillCalculateLayout:rootConstrainedSize];

Source/ASDisplayNode.h

@@ -94,7 +94,15 @@ AS_EXTERN NSInteger const ASDefaultDrawingPriority;
  *
  */
 
-@interface ASDisplayNode : NSObject <ASLocking>
+@interface ASDisplayNode : NSObject <ASLocking> {
+@public
+  /**
+   * The _context ivar is unused by Texture, but provided to enable advanced clients to make powerful extensions to base class functionality.
+   * For example, _context can be used to implement category methods on ASDisplayNode that add functionality to all node subclass types.
+   * Code demonstrating this technique can be found in the CatDealsCollectionView example.
+   */
+  void *_context;
+}
 
 /** @name Initializing a node object */