Only call -layout and -layoutDidFinish if the node is already loaded (#285)

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

* Minor change

* Update CHANGELOG

CHANGELOG.md

@@ -27,3 +27,4 @@
 - [Fix] Fix a major regression in our image node contents caching. [Adlai Holler](https://github.com/Adlai-Holler) [#287](https://github.com/TextureGroup/Texture/pull/287)
 - [Fix] Fixed a bug where ASVideoNodeDelegate error reporting callback would crash an app because of not responding to selector. [Sergey Petrachkov](https://github.com/Petrachkov) [#291](https://github.com/TextureGroup/Texture/issues/291)
 - [IGListKit] Add IGListKit headers to public section of Xcode project [Michael Schneider] (https://github.com/maicki)[#286](https://github.com/TextureGroup/Texture/pull/286)
+- [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 @@ ASPrimitiveTraitCollectionDeprecatedImplementation
   }
 }
 
-/// 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 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   ASDisplayNodeAssertThreadAffinity(self);
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
   
+  BOOL loaded = NO;
   {
     ASDN::MutexLocker l(__instanceLock__);
+    loaded = [self _locked_isNodeLoaded];
     CGRect bounds = _threadSafeBounds;
     
     if (CGRectEqualToRect(bounds, CGRectZero)) {
@@ -930,10 +932,13 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   
   [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
@@ -941,6 +946,7 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
   // Hook for subclasses
   ASDisplayNodeAssertMainThread();
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
+  ASDisplayNodeAssertTrue(self.isNodeLoaded);
 }
 
 #pragma mark Calculation
@@ -1082,8 +1088,10 @@ static ASDisplayNodeMethodOverrides GetASDisplayNodeMethodOverrides(Class c)
 
 - (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;