Fix placeholder image is not appearing if size of node changed after initial placement

Author: maicki

AsyncDisplayKit/ASDisplayNode.mm

@@ -1088,7 +1088,13 @@ - (void)__layout
   // with negative sizes after applying margins, which will cause
   // measureWithSizeRange: on subnodes to assert.
   if (!CGRectEqualToRect(bounds, CGRectZero)) {
+    // Handle placeholder layer creation in case the size of the node changed after the initial placeholder layer
+    // was created
+    if ([self _shouldHavePlaceholderLayer]) {
+      [self _setupPlaceholderLayerIfNeeded];
+    }
     _placeholderLayer.frame = bounds;
+  
     [self layout];
     [self layoutDidFinish];
   }

examples_extra/Placeholders/Sample/PostNode.m

@@ -60,6 +60,10 @@ - (instancetype)init
 - (UIImage *)placeholderImage
 {
   CGSize size = self.calculatedSize;
+  if (CGSizeEqualToSize(size, CGSizeZero)) {
+    return nil;
+  }
+  
   UIGraphicsBeginImageContext(size);
   [[UIColor colorWithWhite:0.9 alpha:1] setFill];
   UIRectFill((CGRect){CGPointZero, size});
@@ -78,6 +82,8 @@ - (CGSize)calculateSizeThatFits:(CGSize)constrainedSize
 
 - (void)layout
 {
+  [super layout];
+  
   CGSize textSize = _textNode.calculatedSize;
   CGSize needyChildSize = _needyChildNode.calculatedSize;
 

examples_extra/Placeholders/Sample/SlowpokeImageNode.m

@@ -15,9 +15,14 @@
 
 static CGFloat const kASDKLogoAspectRatio = 2.79;
 
+@interface ASImageNode (ForwardWorkaround)
+// This is a workaround until subclass overwritting of custom drawing class methods is fixed
+- (UIImage *)displayWithParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock;
+@end
+
 @implementation SlowpokeImageNode
 
-+ (UIImage *)displayWithParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock
+- (UIImage *)displayWithParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock
 {
   usleep( (long)(0.5 * USEC_PER_SEC) ); // artificial delay of 0.5s
 
@@ -46,6 +51,10 @@ - (CGSize)calculateSizeThatFits:(CGSize)constrainedSize
 - (UIImage *)placeholderImage
 {
   CGSize size = self.calculatedSize;
+  if (CGSizeEqualToSize(size, CGSizeZero)) {
+    return nil;
+  }
+
   UIGraphicsBeginImageContext(size);
   [[UIColor whiteColor] setFill];
   [[UIColor colorWithWhite:0.9 alpha:1] setStroke];

examples_extra/Placeholders/Sample/SlowpokeTextNode.m

@@ -13,9 +13,14 @@
 
 #import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
 
+@interface ASTextNode (ForwardWorkaround)
+// This is a workaround until subclass overwritting of custom drawing class methods is fixed
+- (void)drawRect:(CGRect)bounds withParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock isRasterizing:(BOOL)isRasterizing;
+@end
+
 @implementation SlowpokeTextNode
 
-+ (void)drawRect:(CGRect)bounds withParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock isRasterizing:(BOOL)isRasterizing
+- (void)drawRect:(CGRect)bounds withParameters:(id<NSObject>)parameters isCancelled:(asdisplaynode_iscancelled_block_t)isCancelledBlock isRasterizing:(BOOL)isRasterizing
 {
   usleep( (long)(1.0 * USEC_PER_SEC) ); // artificial delay of 1.0