Merge pull request #1016 from facebook/RasterizationUnloadingNodes

Ensure that the uncommon __unloadNode codepath does not unintentionally trigger node removal.

Author: appleguy

AsyncDisplayKit/ASDisplayNode.mm

@@ -352,8 +352,9 @@ - (void)dealloc
 - (void)__unloadNode
 {
   ASDisplayNodeAssertThreadAffinity(self);
+  ASDisplayNodeAssert([self isNodeLoaded], @"Implementation shouldn't call __unloadNode if not loaded: %@", self);
   ASDN::MutexLocker l(_propertyLock);
-  
+
   if (_flags.layerBacked)
     _pendingViewState = [_ASPendingState pendingViewStateFromLayer:_layer];
   else

AsyncDisplayKit/Details/_ASDisplayView.mm

@@ -151,8 +151,11 @@ - (void)didMoveToSuperview
         needsSupernodeRemoval = YES;
       }
     } else {
-      // If supernode is loaded but our superview is nil, the user manually removed us, so disconnect supernode.
-      needsSupernodeRemoval = supernodeLoaded;
+      // If supernode is loaded but our superview is nil, the user likely manually removed us, so disconnect supernode.
+      // The unlikely alternative: we are in __unloadNode, with shouldRasterizeSubnodes just having been turned on.
+      // In the latter case, we don't want to disassemble the node hierarchy because all views are intentionally being destroyed.
+      BOOL nodeIsRasterized = ((_node.hierarchyState & ASHierarchyStateRasterized) == ASHierarchyStateRasterized);
+      needsSupernodeRemoval = (supernodeLoaded && !nodeIsRasterized);
     }
 
     if (needsSupernodeRemoval) {

AsyncDisplayKit/Private/_ASPendingState.m

@@ -798,8 +798,13 @@ - (void)applyToView:(UIView *)view
     view.accessibilityIdentifier = accessibilityIdentifier;
 }
 
+// FIXME: Make this more efficient by tracking which properties are set rather than reading everything.
 + (_ASPendingState *)pendingViewStateFromLayer:(CALayer *)layer
 {
+  if (!layer) {
+    return nil;
+  }
+  
   _ASPendingState *pendingState = [[_ASPendingState alloc] init];
 
   pendingState.anchorPoint = layer.anchorPoint;
@@ -877,8 +882,13 @@ + (_ASPendingState *)pendingViewStateFromLayer:(CALayer *)layer
   return pendingState;
 }
 
+// FIXME: Make this more efficient by tracking which properties are set rather than reading everything.
 + (_ASPendingState *)pendingViewStateFromView:(UIView *)view
 {
+  if (!view) {
+    return nil;
+  }
+  
   _ASPendingState *pendingState = [[_ASPendingState alloc] init];
 
   CALayer *layer = view.layer;

examples/SocialAppLayout/Sample/ViewController.m

@@ -134,4 +134,18 @@ - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger
     return _socialAppDataSource.count;
 }
 
+- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
+{
+    PostNode *postNode = (PostNode *)[_tableView nodeForRowAtIndexPath:indexPath];
+    Post *post = _socialAppDataSource[indexPath.row];
+  
+    BOOL shouldRasterize = postNode.shouldRasterizeDescendants;
+    shouldRasterize = !shouldRasterize;
+    postNode.shouldRasterizeDescendants = shouldRasterize;
+    
+    NSLog(@"%@ rasterization for %@'s post: %@", shouldRasterize ? @"Enabling" : @"Disabling", post.name, postNode);
+    
+    [tableView deselectRowAtIndexPath:indexPath animated:YES];
+}
+
 @end