Add support for sectionInset in ASCollectionView in property and delegate form

AsyncDisplayKit/ASCollectionView.h

@@ -320,6 +320,19 @@
  */
 - (BOOL)shouldBatchFetchForCollectionView:(ASCollectionView *)collectionView;
 
+/**
+ * Passthrough support to UICollectionViewDelegateFlowLayout sectionInset behavior.
+ *
+ * @param collectionView The sender.
+ * @param collectionViewLayout The layout object requesting the information.
+ * #param section The index number of the section whose insets are needed.
+ *
+ * @discussion The same rules apply as the UICollectionView implementation, but this can also be used without a UICollectionViewFlowLayout.
+ * https://developer.apple.com/library/ios/documentation/UIKit/Reference/UICollectionViewDelegateFlowLayout_protocol/index.html#//apple_ref/occ/intfm/UICollectionViewDelegateFlowLayout/collectionView:layout:insetForSectionAtIndex:
+ *
+ */
+- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section;
+
 @end
 
 @interface ASCollectionView (Deprecated)

AsyncDisplayKit/ASCollectionView.mm

@@ -118,6 +118,7 @@ static BOOL _isInterceptedSelector(SEL sel)
   NSMutableArray *_batchUpdateBlocks;
 
   BOOL _asyncDataFetchingEnabled;
+  BOOL _implementsInsetSection;
 
   ASBatchContext *_batchContext;
 }
@@ -164,6 +165,8 @@ static BOOL _isInterceptedSelector(SEL sel)
 
   _performingBatchUpdates = NO;
   _batchUpdateBlocks = [NSMutableArray array];
+  
+  _implementsInsetSection = ([_asyncDelegate respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)] ? 1 : 0);
 
   [self registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"_ASCollectionViewCell"];
   
@@ -511,11 +514,16 @@ static BOOL _isInterceptedSelector(SEL sel)
 - (CGSize)dataController:(ASDataController *)dataController constrainedSizeForNodeAtIndexPath:(NSIndexPath *)indexPath
 {
   CGSize restrainedSize = self.bounds.size;
+  UIEdgeInsets sectionInset = [(UICollectionViewFlowLayout *)self.collectionViewLayout sectionInset];
+  
+  if (_implementsInsetSection) {
+    sectionInset = [_asyncDelegate collectionView:self layout:self.collectionViewLayout insetForSectionAtIndex:indexPath.section];
+  }
 
   if (ASScrollDirectionContainsHorizontalDirection([self scrollableDirections])) {
-    restrainedSize.width = FLT_MAX;
+    restrainedSize.width = MAX(0, FLT_MAX - sectionInset.left - sectionInset.right);
   } else {
-    restrainedSize.height = FLT_MAX;
+    restrainedSize.height = MAX(0, FLT_MAX - sectionInset.top - sectionInset.bottom);
   }
 
   return restrainedSize;

examples/ASCollectionView/Sample/ViewController.m

@@ -95,4 +95,8 @@
   [context completeBatchFetching:YES];
 }
 
+- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
+  return UIEdgeInsetsMake(20.0, 20.0, 20.0, 20.0);
+}
+
 @end