Batch fetch with small data sets

AsyncDisplayKit/ASCollectionView.mm

@@ -386,11 +386,12 @@ static BOOL _isInterceptedSelector(SEL sel)
 
 - (BOOL)shouldBatchFetch
 {
-  if ([_asyncDelegate respondsToSelector:@selector(shouldBatchFetchForCollectionView:)]) {
+  // if the delegate does not respond to this method, there is no point in starting to fetch
+  BOOL canFetch = [_asyncDelegate respondsToSelector:@selector(collectionView:willBeginBatchFetchWithContext:)];
+  if (canFetch && [_asyncDelegate respondsToSelector:@selector(shouldBatchFetchForCollectionView:)]) {
     return [_asyncDelegate shouldBatchFetchForCollectionView:self];
   } else {
-    // if the delegate does not respond to this method, there is no point in starting to fetch
-    return [_asyncDelegate respondsToSelector:@selector(collectionView:willBeginBatchFetchWithContext:)];
+    return canFetch;
   }
 }
 

AsyncDisplayKit/ASTableView.mm

@@ -392,11 +392,12 @@ static BOOL _isInterceptedSelector(SEL sel)
 
 - (BOOL)shouldBatchFetch
 {
-  if ([_asyncDelegate respondsToSelector:@selector(shouldBatchFetchForTableView:)]) {
+  // if the delegate does not respond to this method, there is no point in starting to fetch
+  BOOL canFetch = [_asyncDelegate respondsToSelector:@selector(tableView:willBeginBatchFetchWithContext:)];
+  if (canFetch && [_asyncDelegate respondsToSelector:@selector(shouldBatchFetchForTableView:)]) {
     return [_asyncDelegate shouldBatchFetchForTableView:self];
   } else {
-    // if the delegate does not respond to this method, there is no point in starting to fetch
-    return [_asyncDelegate respondsToSelector:@selector(tableView:willBeginBatchFetchWithContext:)];
+    return canFetch;
   }
 }
 

AsyncDisplayKit/Details/ASBatchFetching.m

@@ -19,16 +19,14 @@ BOOL ASDisplayShouldFetchBatchForContext(ASBatchContext *context,
     return NO;
   }
 
-  // no fetching for null states
-  if (leadingScreens <= 0.0 ||
-      CGPointEqualToPoint(targetOffset, CGPointZero) ||
-      CGSizeEqualToSize(contentSize, CGSizeZero) ||
-      CGRectEqualToRect(bounds, CGRectZero)) {
+  // only Up and Left scrolls are currently supported (tail loading)
+  if (scrollDirection != ASScrollDirectionUp && scrollDirection != ASScrollDirectionLeft) {
     return NO;
   }
 
-  // only Up and Left scrolls are currently supported (tail loading)
-  if (scrollDirection != ASScrollDirectionUp && scrollDirection != ASScrollDirectionLeft) {
+  // no fetching for null states
+  if (leadingScreens <= 0.0 ||
+      CGRectEqualToRect(bounds, CGRectZero)) {
     return NO;
   }
 
@@ -44,8 +42,11 @@ BOOL ASDisplayShouldFetchBatchForContext(ASBatchContext *context,
     contentLength = contentSize.width;
   }
 
+  // target offset will always be 0 if the content size is smaller than the viewport
+  BOOL hasSmallContent = offset == 0.0 && contentLength < viewLength;
+
   CGFloat triggerDistance = viewLength * leadingScreens;
   CGFloat remainingDistance = contentLength - viewLength - offset;
 
-  return remainingDistance <= triggerDistance;
+  return hasSmallContent || remainingDistance <= triggerDistance;
 }

AsyncDisplayKitTests/ASBatchFetchingTests.m

@@ -99,4 +99,20 @@
   XCTAssert(shouldFetch == YES, @"Fetch should begin when vertically scrolling past the content size");
 }
 
+- (void)testVerticalScrollingSmallContentSize {
+  CGFloat screen = 1.0;
+  ASBatchContext *context = [[ASBatchContext alloc] init];
+  // when the content size is < screen size, the target offset will always be 0
+  BOOL shouldFetch = ASDisplayShouldFetchBatchForContext(context, ASScrollDirectionUp, VERTICAL_RECT(screen), VERTICAL_SIZE(screen * 0.5), VERTICAL_OFFSET(0.0), 1.0);
+  XCTAssert(shouldFetch == YES, @"Fetch should begin when the target is 0 and the content size is smaller than the scree");
+}
+
+- (void)testHorizontalScrollingSmallContentSize {
+  CGFloat screen = 1.0;
+  ASBatchContext *context = [[ASBatchContext alloc] init];
+  // when the content size is < screen size, the target offset will always be 0
+  BOOL shouldFetch = ASDisplayShouldFetchBatchForContext(context, ASScrollDirectionLeft, HORIZONTAL_RECT(screen), HORIZONTAL_SIZE(screen * 0.5), HORIZONTAL_OFFSET(0.0), 1.0);
+  XCTAssert(shouldFetch == YES, @"Fetch should begin when the target is 0 and the content size is smaller than the scree");
+}
+
 @end

examples/ASCollectionView/Sample/ViewController.m

@@ -89,7 +89,7 @@
   // unlock the data source to enable data source updating.
 }
 
-- (void)collectionView:(UICollectionView *)collectionView beginBatchFetchingWithContext:(ASBatchContext *)context
+- (void)collectionView:(UICollectionView *)collectionView willBeginBatchFetchWithContext:(ASBatchContext *)context
 {
   NSLog(@"fetch additional content");
   [context completeBatchFetching:YES];

examples/Kittens/Sample/ViewController.m

@@ -55,7 +55,7 @@ static const NSInteger kMaxLitterSize = 100;
 
   // populate our "data source" with some random kittens
 
-  _kittenDataSource = [self createLitterWithSize:kLitterSize];;
+  _kittenDataSource = [self createLitterWithSize:kLitterSize];
 
   return self;
 }
@@ -63,7 +63,7 @@ static const NSInteger kMaxLitterSize = 100;
 - (NSArray *)createLitterWithSize:(NSInteger)litterSize
 {
   NSMutableArray *kittens = [NSMutableArray arrayWithCapacity:litterSize];
-  for (NSInteger i = 0; i < kLitterSize; i++) {
+  for (NSInteger i = 0; i < litterSize; i++) {
     u_int32_t deltaX = arc4random_uniform(10) - 5;
     u_int32_t deltaY = arc4random_uniform(10) - 5;
     CGSize size = CGSizeMake(350 + 2 * deltaX, 350 + 4 * deltaY);
@@ -140,7 +140,7 @@ static const NSInteger kMaxLitterSize = 100;
   return _kittenDataSource.count < kMaxLitterSize;
 }
 
-- (void)tableView:(UITableView *)tableView beginBatchFetchingWithContext:(ASBatchContext *)context
+- (void)tableView:(UITableView *)tableView willBeginBatchFetchWithContext:(ASBatchContext *)context
 {
   NSLog(@"adding kitties");
   dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{