Only call -layout and -layoutDidFinish if the node is already loaded

CHANGELOG.md

@@ -24,4 +24,5 @@
 - [Layout] Extract layout implementation code into it's own subcategories [Michael Schneider] (https://github.com/maicki)[#272](https://github.com/TextureGroup/Texture/pull/272)
 - [Fix] Fix a potential crash when cell nodes that need layout are deleted during the same runloop.  [Adlai Holler](https://github.com/Adlai-Holler) [#279](https://github.com/TextureGroup/Texture/pull/279)
 - [Batch fetching] Add ASBatchFetchingDelegate that takes scroll velocity and remaining time into account [Huy Nguyen](https://github.com/nguyenhuy) [#281](https://github.com/TextureGroup/Texture/pull/281)
+- [Layout] Ensure -layout and -layoutDidFinish are called only if a node is loaded. [Huy Nguyen](https://github.com/nguyenhuy) [#285](https://github.com/TextureGroup/Texture/pull/285)
 

Source/ASDisplayNode+Layout.mm

@@ -293,7 +293,6 @@ - (void)displayNodeDidInvalidateSizeNewSize:(CGSize)size
   }
 }
 
-/// Needs to be called with lock held
 - (void)_locked_measureNodeWithBoundsIfNecessary:(CGRect)bounds
 {
   // Check if we are a subnode in a layout transition.

Source/ASDisplayNode.mm

@@ -902,8 +902,10 @@ - (void)__layout
   ASDisplayNodeAssertThreadAffinity(self);
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
 
+  BOOL loaded = NO;
   {
     ASDN::MutexLocker l(__instanceLock__);
+    loaded = [self _locked_isNodeLoaded];
     CGRect bounds = _threadSafeBounds;
 
     if (CGRectEqualToRect(bounds, CGRectZero)) {
@@ -930,17 +932,21 @@ - (void)__layout
 
   [self _layoutSublayouts];
 
-  ASPerformBlockOnMainThread(^{
-    [self layout];
-    [self layoutDidFinish];
-  });
+  // Per API contract, `-layout` and `-layoutDidFinish` are called only if the node is loaded. 
+  if (loaded) {
+    ASPerformBlockOnMainThread(^{
+      [self layout];
+      [self layoutDidFinish];
+    });
+  }
 }
 
 - (void)layoutDidFinish
 {
   // Hook for subclasses
   ASDisplayNodeAssertMainThread();
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
+  ASDisplayNodeAssertTrue(self.isNodeLoaded);
 }
 
 #pragma mark Calculation
@@ -1082,8 +1088,10 @@ - (ASLayoutSpec *)layoutSpecThatFits:(ASSizeRange)constrainedSize
 
 - (void)layout
 {
+  // Hook for subclasses
   ASDisplayNodeAssertMainThread();
-  // Subclass hook
+  ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
+  ASDisplayNodeAssertTrue(self.isNodeLoaded);
 }
 
 #pragma mark Layout Transition

Source/Private/ASDisplayNodeInternal.h

@@ -234,7 +234,9 @@ FOUNDATION_EXPORT NSString * const ASRenderingEngineDidDisplayNodesScheduledBefo
 - (void)__setNeedsDisplay;
 
 /**
- * Called from [CALayer layoutSublayers:]. Executes the layout pass for the node
+ * Called whenever the node needs to layout its subnodes and, if it's already loaded, its subviews. Executes the layout pass for the node
+ *
+ * This method is thread-safe but asserts thread affinity.
  */
 - (void)__layout;