Implement UICollectionViewFlowLayout heuristics in a default inspector

AsyncDisplayKit/ASCollectionView.mm

@@ -688,21 +688,6 @@ static BOOL _isInterceptedSelector(SEL sel)
   return [_asyncDataSource collectionView:self numberOfItemsInSection:section];
 }
 
-- (ASSizeRange)dataController:(ASCollectionDataController *)dataController constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
-{
-  return [self.layoutDelegate collectionView:self constrainedSizeForSupplementaryNodeOfKind:kind atIndexPath:indexPath];
-}
-
-- (NSUInteger)dataController:(ASCollectionDataController *)dataController supplementaryViewsOfKind:(NSString *)kind inSection:(NSUInteger)section
-{
-  return [self.layoutDelegate collectionView:self supplementaryViewsOfKind:kind inSection:section];
-}
-
-- (NSUInteger)dataController:(ASCollectionDataController *)dataController numberOfSectionsForSupplementaryKind:(NSString *)kind;
-{
-  return [self.layoutDelegate collectionView:self numberOfSectionsForSupplementaryKind:kind];
-}
-
 - (NSUInteger)numberOfSectionsInDataController:(ASDataController *)dataController {
   if ([_asyncDataSource respondsToSelector:@selector(numberOfSectionsInCollectionView:)]) {
     return [_asyncDataSource numberOfSectionsInCollectionView:self];
@@ -731,8 +716,24 @@ static BOOL _isInterceptedSelector(SEL sel)
   }
 }
 
-#pragma mark -
-#pragma mark ASRangeControllerDelegate.
+#pragma mark - ASCollectionViewDataControllerSource Supplementary view support
+
+- (ASSizeRange)dataController:(ASCollectionDataController *)dataController constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
+{
+  return [_layoutDelegate collectionView:self constrainedSizeForSupplementaryNodeOfKind:kind atIndexPath:indexPath];
+}
+
+- (NSUInteger)dataController:(ASCollectionDataController *)dataController supplementaryViewsOfKind:(NSString *)kind inSection:(NSUInteger)section
+{
+  return [_layoutDelegate collectionView:self supplementaryViewsOfKind:kind inSection:section];
+}
+
+- (NSUInteger)dataController:(ASCollectionDataController *)dataController numberOfSectionsForSupplementaryKind:(NSString *)kind;
+{
+  return [_layoutDelegate collectionView:self numberOfSectionsForSupplementaryKind:kind];
+}
+
+#pragma mark - ASRangeControllerDelegate.
 
 - (void)rangeControllerBeginUpdates:(ASRangeController *)rangeController {
   ASDisplayNodeAssertMainThread();

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.h

@@ -14,10 +14,19 @@
 
 @protocol ASCollectionViewLayoutInspecting <NSObject>
 
+/**
+ * Asks the inspector 
+ */
 - (ASSizeRange)collectionView:(ASCollectionView *)collectionView constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
 
+/**
+ * Asks the inspector for the number of supplementary sections in the collection view for the given kind.
+ */
 - (NSUInteger)collectionView:(ASCollectionView *)collectionView numberOfSectionsForSupplementaryKind:(NSString *)kind;
 
+/**
+ * Asks the inspector for the number of supplementary views for the given kind in the specified section.
+ */
 - (NSUInteger)collectionView:(ASCollectionView *)collectionView supplementaryViewsOfKind:(NSString *)kind inSection:(NSUInteger)section;
 
 @end

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m

@@ -6,32 +6,93 @@
 //
 //
 
+#import <UIKit/UIKit.h>
+
 #import "ASCollectionViewFlowLayoutInspector.h"
 
 #import "ASCollectionView.h"
 
-@implementation ASCollectionViewFlowLayoutInspector
+@implementation ASCollectionViewFlowLayoutInspector {
+  BOOL _delegateImplementsReferenceSizeForHeader;
+  BOOL _delegateImplementsReferenceSizeForFooter;
+}
+
+#pragma mark - Accessors
+
+- (void)setLayout:(UICollectionViewFlowLayout *)layout
+{
+  _layout = layout;
+  _delegateImplementsReferenceSizeForHeader = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForHeaderInSection:)];
+  _delegateImplementsReferenceSizeForFooter = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForFooterInSection:)];
+}
+
+#pragma mark - ASCollectionViewLayoutInspecting
 
 - (ASSizeRange)collectionView:(ASCollectionView *)collectionView constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
 {
-  // TODO: Implement some heuristic that follows the width/height constraints of header and footer supplementary views
-  return ASSizeRangeMake(CGSizeZero, CGSizeMake(FLT_MAX, FLT_MAX));
+  CGSize constrainedSize = CGSizeMake(FLT_MAX, FLT_MAX);
+  CGSize supplementarySize = [self sizeForSupplementaryViewOfKind:kind inSection:indexPath.section];
+  if (_layout.scrollDirection == UICollectionViewScrollDirectionVertical) {
+    constrainedSize.height = supplementarySize.height;
+  } else {
+    constrainedSize.width = supplementarySize.width;
+  }
+  return ASSizeRangeMake(CGSizeZero, constrainedSize);
 }
 
-- (NSUInteger)collectionView:(ASCollectionView *)collectionView numberOfSectionsForSupplementaryKind:(NSString *)kind {
-  return self.collectionView.numberOfSections;
+- (NSUInteger)collectionView:(ASCollectionView *)collectionView numberOfSectionsForSupplementaryKind:(NSString *)kind
+{
+  return [collectionView.asyncDataSource numberOfSectionsInCollectionView:collectionView];
 }
 
 - (NSUInteger)collectionView:(ASCollectionView *)collectionView supplementaryViewsOfKind:(NSString *)kind inSection:(NSUInteger)section
 {
-  NSUInteger count = 0;
-  if (self.layout.headerReferenceSize.width > 0 || self.layout.headerReferenceSize.height > 0) {
-    count++;
+  return [self layoutHasSupplementaryViewOfKind:kind inSection:section] ? 1 : 0;
+}
+
+#pragma mark - Private helpers
+
+- (CGSize)sizeForSupplementaryViewOfKind:(NSString *)kind inSection:(NSUInteger)section
+{
+  if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
+    if (_delegateImplementsReferenceSizeForHeader) {
+      return [[self layoutDelegate] collectionView:_collectionView layout:_layout referenceSizeForHeaderInSection:section];
+    } else {
+      return [self.layout headerReferenceSize];
+    }
+  } else if ([kind isEqualToString:UICollectionElementKindSectionFooter]) {
+    if (_delegateImplementsReferenceSizeForFooter) {
+      return [[self layoutDelegate] collectionView:_collectionView layout:_layout referenceSizeForFooterInSection:section];
+    } else {
+      return [self.layout footerReferenceSize];
+    }
+  } else {
+    return CGSizeZero;
   }
-  if (self.layout.footerReferenceSize.width > 0 || self.layout.footerReferenceSize.height > 0) {
-    count++;
+}
+
+- (BOOL)layoutHasSupplementaryViewOfKind:(NSString *)kind inSection:(NSUInteger)section
+{
+  CGSize size = [self sizeForSupplementaryViewOfKind:kind inSection:section];
+  if ([self usedLayoutValueForSize:size] > 0) {
+    return YES;
+  } else {
+    return NO;
   }
-  return count;
+}
+
+- (CGFloat)usedLayoutValueForSize:(CGSize)size
+{
+  if (_layout.scrollDirection == UICollectionViewScrollDirectionVertical) {
+    return size.height;
+  } else {
+    return size.width;
+  }
+}
+
+- (id<UICollectionViewDelegateFlowLayout>)layoutDelegate
+{
+  return (id<UICollectionViewDelegateFlowLayout>)self.collectionView.delegate;
 }
 
 @end