Handle initial sizing delegate implementation in flow layout inspector

AsyncDisplayKit/ASCollectionView.mm

@@ -228,13 +228,8 @@ static BOOL _isInterceptedSelector(SEL sel)
   
   // Register the default layout inspector delegate for flow layouts, custom layouts
   // will need to roll their own ASCollectionViewLayoutInspecting implementation.
-  if ([layout asdk_isFlowLayout]) {
-    _flowLayoutInspector = [[ASCollectionViewFlowLayoutInspector alloc] init];
-    _flowLayoutInspector.layout = (UICollectionViewFlowLayout *)layout;
-    _flowLayoutInspector.collectionView = self;
-    _layoutDelegate = _flowLayoutInspector;
-  }
-
+  _layoutDelegate = [self flowLayoutInspector];
+  
   _registeredSupplementaryKinds = [NSMutableArray array];
   
   self.backgroundColor = [UIColor whiteColor];
@@ -252,6 +247,21 @@ static BOOL _isInterceptedSelector(SEL sel)
   super.dataSource = nil;
 }
 
+/**
+ * A layout inspector implementation specific for the sizing behavior of UICollectionViewFlowLayouts
+ *
+ * @discussion Will return nil if the current layout is not a flow layout
+ */
+- (ASCollectionViewFlowLayoutInspector *)flowLayoutInspector
+{
+    if (_flowLayoutInspector == nil) {
+        UICollectionViewFlowLayout *layout = (UICollectionViewFlowLayout *)self.collectionViewLayout;
+        _flowLayoutInspector = [[ASCollectionViewFlowLayoutInspector alloc] initWithCollectionView:self
+                                                                                        flowLayout:layout];
+    }
+    return _flowLayoutInspector;
+}
+
 #pragma mark -
 #pragma mark Overrides.
 
@@ -326,6 +336,8 @@ static BOOL _isInterceptedSelector(SEL sel)
     super.delegate = (id<UICollectionViewDelegate>)_proxyDelegate;
     _asyncDelegateImplementsInsetSection = ([_asyncDelegate respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)] ? 1 : 0);
   }
+
+  _flowLayoutInspector.collectionView = self;
 }
 
 - (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.h

@@ -33,8 +33,10 @@
 
 @interface ASCollectionViewFlowLayoutInspector : NSObject <ASCollectionViewLayoutInspecting>
 
-@property (nonatomic, weak) ASCollectionView *collectionView;
 @property (nonatomic, weak) UICollectionViewFlowLayout *layout;
+@property (nonatomic, weak) ASCollectionView *collectionView;
+
+- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView flowLayout:(UICollectionViewFlowLayout *)flowLayout;
 
 - (ASSizeRange)collectionView:(ASCollectionView *)collectionView constrainedSizeForSupplementaryNodeOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath;
 

AsyncDisplayKit/Details/ASCollectionViewFlowLayoutInspector.m

@@ -19,11 +19,25 @@
 
 #pragma mark - Accessors
 
-- (void)setLayout:(UICollectionViewFlowLayout *)layout
+- (instancetype)initWithCollectionView:(ASCollectionView *)collectionView flowLayout:(UICollectionViewFlowLayout *)flowLayout
 {
-  _layout = layout;
-  _delegateImplementsReferenceSizeForHeader = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForHeaderInSection:)];
-  _delegateImplementsReferenceSizeForFooter = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForFooterInSection:)];
+    if (flowLayout == nil) {
+        return nil;
+    }
+
+    self = [super init];
+    if (self != nil) {
+        self.collectionView = collectionView;
+        _layout = flowLayout;
+    }
+    return self;
+}
+
+- (void)setCollectionView:(ASCollectionView *)collectionView
+{
+    _collectionView = collectionView;
+    _delegateImplementsReferenceSizeForHeader = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForHeaderInSection:)];
+    _delegateImplementsReferenceSizeForFooter = [[self layoutDelegate] respondsToSelector:@selector(collectionView:layout:referenceSizeForFooterInSection:)];
 }
 
 #pragma mark - ASCollectionViewLayoutInspecting
@@ -94,9 +108,9 @@
   }
 }
 
-- (id<UICollectionViewDelegateFlowLayout>)layoutDelegate
+- (id<ASCollectionViewDelegateFlowLayout>)layoutDelegate
 {
-  return (id<UICollectionViewDelegateFlowLayout>)self.collectionView.delegate;
+  return (id<ASCollectionViewDelegateFlowLayout>)_collectionView.asyncDelegate;
 }
 
 @end