Merge pull request #303 from facebook/enable_async_data_fetching

Move ASTableView & ASCollectionView data fetching to background thread

AsyncDisplayKit/Details/ASDataController.h

@@ -28,13 +28,23 @@ typedef NSUInteger ASDataControllerAnimationOptions;
 /**
  Fetch the number of rows in specific section.
  */
-- (NSUInteger)dataController:(ASDataController *)dataControllre rowsInSection:(NSUInteger)section;
+- (NSUInteger)dataController:(ASDataController *)dataController rowsInSection:(NSUInteger)section;
 
 /**
  Fetch the number of sections.
  */
 - (NSUInteger)dataControllerNumberOfSections:(ASDataController *)dataController;
 
+/**
+ Lock the data source for data fetching.
+ */
+- (void)dataControllerLockDataSource;
+
+/**
+ Unlock the data source after data fetching.
+ */
+- (void)dataControllerUnlockDataSource;
+
 @end
 
 /**
@@ -97,6 +107,20 @@ typedef NSUInteger ASDataControllerAnimationOptions;
  */
 @property (nonatomic, weak) id<ASDataControllerDelegate> delegate;
 
+/**
+ *  Designated iniailizer.
+ *
+ * @param asyncDataFetchingEnabled Enable the data fetching in async mode.
+ 
+ * @discussion If enabled, we will fetch data through `dataController:nodeAtIndexPath:` and `dataController:rowsInSection:` in background thread.
+ * Otherwise, the methods will be invoked synchronically in calling thread. Enabling data fetching in async mode could avoid blocking main thread
+ * while allocating cell on main thread, which is frequently reported issue for handing large scale data. On another hand, the application code
+ * will take the responsibility to avoid data inconsistence. Specifically, we will lock the data source through `dataControllerLockDataSource`,
+ * and unlock it by `dataControllerUnlockDataSource` after the data fetching. The application should not update the data source while
+ * the data source is locked.
+ */
+- (instancetype)initWithAsyncDataFetching:(BOOL)asyncDataFetchingEnabled;
+
 /** @name Initial loading */
 
 - (void)initialDataLoadingWithAnimationOption:(ASDataControllerAnimationOptions)animationOption;