Support custom working-range logic.

AsyncDisplayKit/ASCollectionView.h

@@ -34,6 +34,13 @@
  */
 @property (nonatomic, assign) ASRangeTuningParameters rangeTuningParameters;
 
+/**
+ * @abstract An optional block which can perform custom calculation for working range.
+ *
+ * @discussion Can be used to provide custom working range logic for custom layouts.
+ */
+@property (nonatomic, assign) asrangecontroller_working_range_calculation_block_t workingRangeCalculationBlock;
+
 /**
  * Reload everything from scratch, destroying the working range and all cached nodes.
  *

AsyncDisplayKit/ASCollectionView.m

@@ -165,6 +165,16 @@ static BOOL _isInterceptedSelector(SEL sel)
   _rangeController.tuningParameters = tuningParameters;
 }
 
+- (asrangecontroller_working_range_calculation_block_t)workingRangeCalculationBlock
+{
+  return _rangeController.workingRangeCalculationBlock;
+}
+
+- (void)setWorkingRangeCalculationBlock:(asrangecontroller_working_range_calculation_block_t)workingRangeCalculationBlock
+{
+  _rangeController.workingRangeCalculationBlock = workingRangeCalculationBlock;
+}
+
 - (void)appendNodesWithIndexPaths:(NSArray *)indexPaths
 {
   [_rangeController appendNodesWithIndexPaths:indexPaths];

AsyncDisplayKit/Details/ASRangeController.h

@@ -16,6 +16,13 @@ typedef struct {
   CGFloat leadingBufferScreenfuls;
 } ASRangeTuningParameters;
 
+typedef NS_ENUM(NSInteger, ASScrollDirection) {
+  ASScrollDirectionBackward,
+  ASScrollDirectionForward,
+};
+
+typedef NSRange (^asrangecontroller_working_range_calculation_block_t)(ASRangeTuningParameters params, ASScrollDirection scrollDirection, NSRange visibleRange, NSArray *nodeSizes, CGSize viewport);
+
 @protocol ASRangeControllerDelegate;
 
 
@@ -99,6 +106,13 @@ typedef struct {
  */
 @property (nonatomic, assign) ASRangeTuningParameters tuningParameters;
 
+/**
+ * @abstract An optional block which can perform custom calculation for working range.
+ *
+ * @discussion Can be used to provide custom working range logic for custom layouts.
+ */
+@property (nonatomic, readwrite, copy) asrangecontroller_working_range_calculation_block_t workingRangeCalculationBlock;
+
 @end
 
 

AsyncDisplayKit/Details/ASRangeController.mm

@@ -13,11 +13,6 @@
 #import "ASDisplayNodeInternal.h"
 #import "ASRangeControllerInternal.h"
 
-typedef NS_ENUM(NSInteger, ASScrollDirection) {
-  ASScrollDirectionBackward,
-  ASScrollDirectionForward,
-};
-
 @interface ASRangeController () {
   // index path -> node mapping
   NSMutableDictionary *_nodes;
@@ -472,11 +467,21 @@ static NSRange ASCalculateWorkingRange(ASRangeTuningParameters params, ASScrollD
 
 - (void)recalculateWorkingRange
 {
-  NSRange workingRange = ASCalculateWorkingRange(_tuningParameters,
+  NSRange workingRange;
+  if (self.workingRangeCalculationBlock != NULL) {
+    workingRange = self.workingRangeCalculationBlock(_tuningParameters,
                                                      _scrollDirection,
                                                      _visibleRange,
                                                      _nodeSizes,
                                                      [_delegate rangeControllerViewportSize:self]);
+  } else {
+    workingRange = ASCalculateWorkingRange(_tuningParameters,
+                                           _scrollDirection,
+                                           _visibleRange,
+                                           _nodeSizes,
+                                           [_delegate rangeControllerViewportSize:self]);
+  }
+  
   [self setWorkingRange:workingRange];
 }