[ASCollectionViewLayoutInspecting] make -scrollableDirections required (#2543)

* [ASCollectionViewLayoutInspecting] make -scrollableDirections a required method

* doh!

* fixed?

* add assert per @appleguy's comment

* use self.layoutInspector, add check at the start of didChangeBounds...

AsyncDisplayKit/ASCollectionView.mm

@@ -212,7 +212,6 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   struct {
     unsigned int didChangeCollectionViewDataSource:1;
     unsigned int didChangeCollectionViewDelegate:1;
-	unsigned int scrollableDirections:1;
   } _layoutInspectorFlags;
 }
 
@@ -515,7 +514,6 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
   
   _layoutInspectorFlags.didChangeCollectionViewDataSource = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDataSource:)];
   _layoutInspectorFlags.didChangeCollectionViewDelegate = [_layoutInspector respondsToSelector:@selector(didChangeCollectionViewDelegate:)];
-  _layoutInspectorFlags.scrollableDirections = [_layoutInspector respondsToSelector:@selector(scrollableDirections)];
 }
 
 - (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType
@@ -1117,23 +1115,8 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
 
 - (ASScrollDirection)scrollableDirections
 {
-  //Cache results of layoutInspector to ensure flags are up to date if getter lazily loads a new one.
-  id<ASCollectionViewLayoutInspecting> layoutInspector = self.layoutInspector;
-  if (_layoutInspectorFlags.scrollableDirections) {
-    return [layoutInspector scrollableDirections];
-  } else {
-    ASScrollDirection scrollableDirection = ASScrollDirectionNone;
-    CGFloat totalContentWidth = self.contentSize.width + self.contentInset.left + self.contentInset.right;
-    CGFloat totalContentHeight = self.contentSize.height + self.contentInset.top + self.contentInset.bottom;
-    
-    if (self.alwaysBounceHorizontal || totalContentWidth > self.bounds.size.width) { // Can scroll horizontally.
-      scrollableDirection |= ASScrollDirectionHorizontalDirections;
-    }
-    if (self.alwaysBounceVertical || totalContentHeight > self.bounds.size.height) { // Can scroll vertically.
-      scrollableDirection |= ASScrollDirectionVerticalDirections;
-    }
-    return scrollableDirection;
-  }
+  ASDisplayNodeAssertNotNil(self.layoutInspector, @"Layout inspector should be assigned.");
+  return [self.layoutInspector scrollableDirections];
 }
 
 - (ASScrollDirection)flowLayoutScrollableDirections:(UICollectionViewFlowLayout *)flowLayout {
@@ -1672,6 +1655,9 @@ static NSString * const kCellReuseIdentifier = @"_ASCollectionViewCell";
  */
 - (void)layer:(CALayer *)layer didChangeBoundsWithOldValue:(CGRect)oldBounds newValue:(CGRect)newBounds
 {
+  if (self.collectionViewLayout == nil) {
+    return;
+  }
   CGSize lastUsedSize = _lastBoundsSizeUsedForMeasuringNodes;
   if (CGSizeEqualToSize(lastUsedSize, newBounds.size)) {
     return;

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.h

@@ -27,6 +27,11 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (ASSizeRange)collectionView:(ASCollectionView *)collectionView constrainedSizeForNodeAtIndexPath:(NSIndexPath *)indexPath;
 
+/**
+ * Return the directions in which your collection view can scroll
+ */
+- (ASScrollDirection)scrollableDirections;
+
 @optional
 
 /**
@@ -53,11 +58,6 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)didChangeCollectionViewDataSource:(nullable id<ASCollectionDataSource>)dataSource;
 
-/**
- * Return the directions in which your collection view can scroll
- */
-- (ASScrollDirection)scrollableDirections;
-
 #pragma mark Deprecated Methods
 
 /**

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m

@@ -79,6 +79,12 @@ static inline ASSizeRange NodeConstrainedSizeForScrollDirection(ASCollectionView
   return NodeConstrainedSizeForScrollDirection(collectionView);
 }
 
+- (ASScrollDirection)scrollableDirections
+{
+  ASDisplayNodeAssert(NO, @"layoutInspector object must implement -scrollableDirections %@", self);
+  return ASScrollDirectionNone;
+}
+
 - (ASSizeRange)collectionView:(ASCollectionView *)collectionView constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
 {
   ASDisplayNodeAssert(NO, @"To support supplementary nodes in ASCollectionView, it must have a layoutInspector for layout inspection. (See ASCollectionViewFlowLayoutInspector for an example.)");

examples/CustomCollectionView/Sample/MosaicCollectionViewLayout.m

@@ -214,6 +214,11 @@
   return ASSizeRangeMake(CGSizeZero, [layout _headerSizeForSection:indexPath.section]);
 }
 
+- (ASScrollDirection)scrollableDirections
+{
+  return ASScrollDirectionVerticalDirections;
+}
+
 /**
  * Asks the inspector for the number of supplementary views for the given kind in the specified section.
  */