Add didEnterHierarchy/didExitHierarchy to ASNodeController. (facebookarchive#1444)

Author: tnorman42

Source/ASDisplayNode+InterfaceState.h

@@ -127,4 +127,22 @@ typedef NS_OPTIONS(NSUInteger, ASInterfaceState)
  */
 - (void)nodeWillCalculateLayout:(ASSizeRange)constrainedSize;
 
+/**
+ * @abstract Called when the node's layer is about to enter the hierarchy.
+ * @discussion May be called more than once if the layer is participating in a higher-level
+ * animation, such as a UIViewController transition. These animations can cause the layer to get
+ * re-parented multiple times, and each time will trigger this call.
+ * @note This method is guaranteed to be called on main.
+ */
+- (void)didEnterHierarchy;
+
+/**
+ * @abstract Called when the node's layer has exited the hierarchy.
+ * @discussion May be called more than once if the layer is participating in a higher-level
+ * animation, such as a UIViewController transition. These animations can cause the layer to get
+ * re-parented multiple times, and each time will trigger this call.
+ * @note This method is guaranteed to be called on main.
+ */
+- (void)didExitHierarchy;
+
 @end

Source/ASDisplayNode.mm

@@ -2874,6 +2874,12 @@ - (void)didEnterHierarchy {
   ASDisplayNodeAssert(!_flags.isExitingHierarchy, @"ASDisplayNode inconsistency. __enterHierarchy and __exitHierarchy are mutually exclusive");
   ASDisplayNodeAssert(_flags.isInHierarchy, @"ASDisplayNode inconsistency. __enterHierarchy and __exitHierarchy are mutually exclusive");
   ASAssertUnlocked(__instanceLock__);
+
+  [self enumerateInterfaceStateDelegates:^(id<ASInterfaceStateDelegate> del) {
+    if ([del respondsToSelector:@selector(didEnterHierarchy)]) {
+      [del didEnterHierarchy];
+    }
+  }];
 }
 
 - (void)didExitHierarchy
@@ -2883,6 +2889,12 @@ - (void)didExitHierarchy
   ASDisplayNodeAssert(!_flags.isEnteringHierarchy, @"ASDisplayNode inconsistency. __enterHierarchy and __exitHierarchy are mutually exclusive");
   ASAssertUnlocked(__instanceLock__);
 
+  [self enumerateInterfaceStateDelegates:^(id<ASInterfaceStateDelegate> del) {
+    if ([del respondsToSelector:@selector(didExitHierarchy)]) {
+      [del didExitHierarchy];
+    }
+  }];
+
   // This case is important when tearing down hierarchies.  We must deliver a visibileStateDidChange:NO callback, as part our API guarantee that this method can be used for
   // things like data analytics about user content viewing.  We cannot call the method in the dealloc as any incidental retain operations in client code would fail.
   // Additionally, it may be that a Standard UIView which is containing us is moving between hierarchies, and we should not send the call if we will be re-added in the

Source/ASNodeController+Beta.h

@@ -44,6 +44,9 @@
 
 - (void)hierarchyDisplayDidFinish ASDISPLAYNODE_REQUIRES_SUPER;
 
+- (void)didEnterHierarchy ASDISPLAYNODE_REQUIRES_SUPER;
+- (void)didExitHierarchy  ASDISPLAYNODE_REQUIRES_SUPER;
+
 /**
  * @discussion Attempts (via ASLockSequence, a backing-off spinlock similar to
  * std::lock()) to lock both the node and its ASNodeController, if one exists.

Source/ASNodeController+Beta.mm

@@ -92,6 +92,9 @@ - (void)interfaceStateDidChange:(ASInterfaceState)newState
 
 - (void)hierarchyDisplayDidFinish {}
 
+- (void)didEnterHierarchy {}
+- (void)didExitHierarchy  {}
+
 - (ASLockSet)lockPair {
   ASLockSet lockSet = ASLockSequence(^BOOL(ASAddLockBlock addLock) {
     if (!addLock(_node)) {