/* Copyright (c) 2014-present, Facebook, Inc.

* All rights reserved.

*

* This source code is licensed under the BSD-style license found in the

* LICENSE file in the root directory of this source tree. An additional grant

* of patent rights can be found in the PATENTS file in the same directory.

*/

#import "ASCollectionView.h"

#import "ASAssert.h"

#import "ASFlowLayoutController.h"

#import "ASRangeController.h"

#import "ASDataController.h"

#import "ASDisplayNodeInternal.h"

#import "ASBatchFetching.h"

const static NSUInteger kASCollectionViewAnimationNone = 0;

#pragma mark -

#pragma mark Proxying.

/**

* ASCollectionView intercepts and/or overrides a few of UICollectionView's critical data source and delegate methods.

*

* Any selector included in this function *MUST* be implemented by ASCollectionView.

*/

static BOOL _isInterceptedSelector(SEL sel)

{

return (

// handled by ASCollectionView node<->cell machinery

sel == @selector(collectionView:cellForItemAtIndexPath:) ||

sel == @selector(collectionView:layout:sizeForItemAtIndexPath:) ||

// handled by ASRangeController

sel == @selector(numberOfSectionsInCollectionView:) ||

sel == @selector(collectionView:numberOfItemsInSection:) ||

// used for ASRangeController visibility updates

sel == @selector(collectionView:willDisplayCell:forItemAtIndexPath:) ||

sel == @selector(collectionView:didEndDisplayingCell:forItemAtIndexPath:) ||

// used for batch fetching API

sel == @selector(scrollViewWillEndDragging:withVelocity:targetContentOffset:)

);

}

/**

* Stand-in for UICollectionViewDataSource and UICollectionViewDelegate. Any method calls we intercept are routed to ASCollectionView;

* everything else leaves AsyncDisplayKit safely and arrives at the original intended data source and delegate.

*/

@interface _ASCollectionViewProxy : NSProxy

- (instancetype)initWithTarget:(id<NSObject>)target interceptor:(ASCollectionView *)interceptor;

@end

@implementation _ASCollectionViewProxy {

id<NSObject> __weak _target;

ASCollectionView * __weak _interceptor;

}

- (instancetype)initWithTarget:(id<NSObject>)target interceptor:(ASCollectionView *)interceptor

{

// -[NSProxy init] is undefined

if (!self) {

return nil;

}

ASDisplayNodeAssert(target, @"target must not be nil");

ASDisplayNodeAssert(interceptor, @"interceptor must not be nil");

_target = target;

_interceptor = interceptor;

return self;

}

- (BOOL)respondsToSelector:(SEL)aSelector

{

ASDisplayNodeAssert(_target, @"target must not be nil"); // catch weak ref's being nilled early

ASDisplayNodeAssert(_interceptor, @"interceptor must not be nil");

return (_isInterceptedSelector(aSelector) || [_target respondsToSelector:aSelector]);

}

- (id)forwardingTargetForSelector:(SEL)aSelector

{

ASDisplayNodeAssert(_target, @"target must not be nil"); // catch weak ref's being nilled early

ASDisplayNodeAssert(_interceptor, @"interceptor must not be nil");

if (_isInterceptedSelector(aSelector)) {

return _interceptor;

}

return [_target respondsToSelector:aSelector] ? _target : nil;

}

@end

#pragma mark -

#pragma mark ASCollectionView.

@interface ASCollectionView () <ASRangeControllerDelegate, ASDataControllerSource> {

_ASCollectionViewProxy *_proxyDataSource;

_ASCollectionViewProxy *_proxyDelegate;

ASDataController *_dataController;

ASRangeController *_rangeController;

ASFlowLayoutController *_layoutController;

BOOL _performingBatchUpdates;

NSMutableArray *_batchUpdateBlocks;

BOOL _asyncDataFetchingEnabled;

ASBatchContext *_batchContext;

}

@property (atomic, assign) BOOL asyncDataSourceLocked;

@end

@implementation ASCollectionView

#pragma mark -

#pragma mark Lifecycle.

- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout

{

return [self initWithFrame:frame collectionViewLayout:layout asyncDataFetching:NO];

}

- (instancetype)initWithFrame:(CGRect)frame collectionViewLayout:(UICollectionViewLayout *)layout asyncDataFetching:(BOOL)asyncDataFetchingEnabled

{

if (!(self = [super initWithFrame:frame collectionViewLayout:layout]))

return nil;

ASDisplayNodeAssert([layout isKindOfClass:UICollectionViewFlowLayout.class], @"only flow layouts are currently supported");

ASFlowLayoutDirection direction = (((UICollectionViewFlowLayout *)layout).scrollDirection == UICollectionViewScrollDirectionHorizontal) ? ASFlowLayoutDirectionHorizontal : ASFlowLayoutDirectionVertical;

_layoutController = [[ASFlowLayoutController alloc] initWithScrollOption:direction];

_rangeController = [[ASRangeController alloc] init];

_rangeController.delegate = self;

_rangeController.layoutController = _layoutController;

_dataController = [[ASDataController alloc] initWithAsyncDataFetching:asyncDataFetchingEnabled];

_dataController.delegate = _rangeController;

_dataController.dataSource = self;

_batchContext = [[ASBatchContext alloc] init];

_leadingScreensForBatching = 1.0;

_asyncDataFetchingEnabled = asyncDataFetchingEnabled;

_asyncDataSourceLocked = NO;

_performingBatchUpdates = NO;

_batchUpdateBlocks = [NSMutableArray array];

[self registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"_ASCollectionViewCell"];

return self;

}

-(void)dealloc {

// a little defense move here.

super.delegate = nil;

super.dataSource = nil;

}

#pragma mark -

#pragma mark Overrides.

- (void)reloadDataWithCompletion:(void (^)())completion

{

ASDisplayNodeAssert(self.asyncDelegate, @"ASCollectionView's asyncDelegate property must be set.");

ASDisplayNodePerformBlockOnMainThread(^{

[super reloadData];

});

[_dataController reloadDataWithAnimationOption:kASCollectionViewAnimationNone completion:completion];

}

- (void)reloadData

{

[self reloadDataWithCompletion:nil];

}

- (void)setDataSource:(id<UICollectionViewDataSource>)dataSource

{

ASDisplayNodeAssert(NO, @"ASCollectionView uses asyncDataSource, not UICollectionView's dataSource property.");

}

- (void)setDelegate:(id<UICollectionViewDelegate>)delegate

{

// Our UIScrollView superclass sets its delegate to nil on dealloc. Only assert if we get a non-nil value here.

ASDisplayNodeAssert(delegate == nil, @"ASCollectionView uses asyncDelegate, not UICollectionView's delegate property.");

}

- (void)setAsyncDataSource:(id<ASCollectionViewDataSource>)asyncDataSource

{

// Note: It's common to check if the value hasn't changed and short-circuit but we aren't doing that here to handle

// the (common) case of nilling the asyncDataSource in the ViewController's dealloc. In this case our _asyncDataSource

// will return as nil (ARC magic) even though the _proxyDataSource still exists. It's really important to nil out

// super.dataSource in this case because calls to _ASTableViewProxy will start failing and cause crashes.

if (asyncDataSource == nil) {

super.dataSource = nil;

_asyncDataSource = nil;

_proxyDataSource = nil;

} else {

_asyncDataSource = asyncDataSource;

_proxyDataSource = [[_ASCollectionViewProxy alloc] initWithTarget:_asyncDataSource interceptor:self];

super.dataSource = (id<UICollectionViewDataSource>)_proxyDataSource;

}

}

- (void)setAsyncDelegate:(id<ASCollectionViewDelegate>)asyncDelegate

{

// Note: It's common to check if the value hasn't changed and short-circuit but we aren't doing that here to handle

// the (common) case of nilling the asyncDelegate in the ViewController's dealloc. In this case our _asyncDelegate

// will return as nil (ARC magic) even though the _proxyDelegate still exists. It's really important to nil out

// super.delegate in this case because calls to _ASTableViewProxy will start failing and cause crashes.

if (asyncDelegate == nil) {

// order is important here, the delegate must be callable while nilling super.delegate to avoid random crashes

// in UIScrollViewAccessibility.

super.delegate = nil;

_asyncDelegate = nil;

_proxyDelegate = nil;

} else {

_asyncDelegate = asyncDelegate;

_proxyDelegate = [[_ASCollectionViewProxy alloc] initWithTarget:_asyncDelegate interceptor:self];

super.delegate = (id<UICollectionViewDelegate>)_proxyDelegate;

}

}

- (void)setTuningParameters:(ASRangeTuningParameters)tuningParameters forRangeType:(ASLayoutRangeType)rangeType

{

[_layoutController setTuningParameters:tuningParameters forRangeType:rangeType];

}

- (ASRangeTuningParameters)tuningParametersForRangeType:(ASLayoutRangeType)rangeType

{

return [_layoutController tuningParametersForRangeType:rangeType];

}

- (ASRangeTuningParameters)rangeTuningParameters

{

return [self tuningParametersForRangeType:ASLayoutRangeTypeRender];

}

- (void)setRangeTuningParameters:(ASRangeTuningParameters)tuningParameters

{

[self setTuningParameters:tuningParameters forRangeType:ASLayoutRangeTypeRender];

}

- (CGSize)calculatedSizeForNodeAtIndexPath:(NSIndexPath *)indexPath

{

return [[_dataController nodeAtIndexPath:indexPath] calculatedSize];

}

- (NSArray *)visibleNodes

{

NSArray *indexPaths = [self indexPathsForVisibleItems];

NSMutableArray *visibleNodes = [[NSMutableArray alloc] init];

[indexPaths enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {

ASCellNode *visibleNode = [self nodeForItemAtIndexPath:obj];

[visibleNodes addObject:visibleNode];

}];

return visibleNodes;

}

#pragma mark Assertions.

- (void)performBatchUpdates:(void (^)())updates completion:(void (^)(BOOL))completion

{

[_dataController beginUpdates];

updates();

[_dataController endUpdatesWithCompletion:completion];

}

- (void)insertSections:(NSIndexSet *)sections

{

[_dataController insertSections:sections withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)deleteSections:(NSIndexSet *)sections

{

[_dataController deleteSections:sections withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)reloadSections:(NSIndexSet *)sections

{

[_dataController reloadSections:sections withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)moveSection:(NSInteger)section toSection:(NSInteger)newSection

{

[_dataController moveSection:section toSection:newSection withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)insertItemsAtIndexPaths:(NSArray *)indexPaths

{

[_dataController insertRowsAtIndexPaths:indexPaths withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)deleteItemsAtIndexPaths:(NSArray *)indexPaths

{

[_dataController deleteRowsAtIndexPaths:indexPaths withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths

{

[_dataController reloadRowsAtIndexPaths:indexPaths withAnimationOption:kASCollectionViewAnimationNone];

}

- (void)moveItemAtIndexPath:(NSIndexPath *)indexPath toIndexPath:(NSIndexPath *)newIndexPath

{

[_dataController moveRowAtIndexPath:indexPath toIndexPath:newIndexPath withAnimationOption:kASCollectionViewAnimationNone];

}

- (ASCellNode *)nodeForItemAtIndexPath:(NSIndexPath *)indexPath

{

return [_dataController nodeAtIndexPath:indexPath];

}

#pragma mark -

#pragma mark Intercepted selectors.

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

{

static NSString *reuseIdentifier = @"_ASCollectionViewCell";

UICollectionViewCell *cell = [self dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

ASCellNode *node = [_dataController nodeAtIndexPath:indexPath];

[_rangeController configureContentView:cell.contentView forCellNode:node];

return cell;

}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath

{

return [[_dataController nodeAtIndexPath:indexPath] calculatedSize];

}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView

{

return [_dataController numberOfSections];

}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section

{

return [_dataController numberOfRowsInSection:section];

}

- (ASScrollDirection)scrollDirection

{

CGPoint scrollVelocity = [self.panGestureRecognizer velocityInView:self.superview];

ASScrollDirection direction = ASScrollDirectionNone;

if (_layoutController.layoutDirection == ASFlowLayoutDirectionHorizontal) {

if (scrollVelocity.x > 0) {

direction = ASScrollDirectionRight;

} else if (scrollVelocity.x < 0) {

direction = ASScrollDirectionLeft;

}

} else {

if (scrollVelocity.y > 0) {

direction = ASScrollDirectionDown;

} else {

direction = ASScrollDirectionUp;

}

}

return direction;

}

- (void)collectionView:(UICollectionView *)collectionView willDisplayCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath

{

[_rangeController visibleNodeIndexPathsDidChangeWithScrollDirection:self.scrollDirection];

if ([_asyncDelegate respondsToSelector:@selector(collectionView:willDisplayNodeForItemAtIndexPath:)]) {

[_asyncDelegate collectionView:self willDisplayNodeForItemAtIndexPath:indexPath];

}

}

- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath

{

[_rangeController visibleNodeIndexPathsDidChangeWithScrollDirection:self.scrollDirection];

if ([_asyncDelegate respondsToSelector:@selector(collectionView:didEndDisplayingNodeForItemAtIndexPath:)]) {

[_asyncDelegate collectionView:self didEndDisplayingNodeForItemAtIndexPath:indexPath];

}

}

#pragma mark -

#pragma mark Batch Fetching

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset

{

[self handleBatchFetchScrollingToOffset:*targetContentOffset];

if ([_asyncDelegate respondsToSelector:@selector(scrollViewWillEndDragging:withVelocity:targetContentOffset:)]) {

[_asyncDelegate scrollViewWillEndDragging:scrollView withVelocity:velocity targetContentOffset:targetContentOffset];

}

}

- (BOOL)shouldBatchFetch

{

// 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 {

return canFetch;

}

}

- (void)handleBatchFetchScrollingToOffset:(CGPoint)targetOffset

{

ASDisplayNodeAssert(_batchContext != nil, @"Batch context should exist");

if (![self shouldBatchFetch]) {

return;

}

if (ASDisplayShouldFetchBatchForContext(_batchContext, [self scrollDirection], self.bounds, self.contentSize, targetOffset, _leadingScreensForBatching)) {

[_batchContext beginBatchFetching];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

[_asyncDelegate collectionView:self willBeginBatchFetchWithContext:_batchContext];

});

}

}

#pragma mark - ASDataControllerSource

- (ASCellNode *)dataController:(ASDataController *)dataController nodeAtIndexPath:(NSIndexPath *)indexPath

{

ASCellNode *node = [_asyncDataSource collectionView:self nodeForItemAtIndexPath:indexPath];

ASDisplayNodeAssert([node isKindOfClass:ASCellNode.class], @"invalid node class, expected ASCellNode");

return node;

}

- (CGSize)dataController:(ASDataController *)dataController constrainedSizeForNodeAtIndexPath:(NSIndexPath *)indexPath

{

CGSize restrainedSize = self.bounds.size;

if (_layoutController.layoutDirection == ASFlowLayoutDirectionHorizontal) {

restrainedSize.width = FLT_MAX;

} else {

restrainedSize.height = FLT_MAX;

}

return restrainedSize;

}

- (NSUInteger)dataController:(ASDataController *)dataController rowsInSection:(NSUInteger)section

{

return [_asyncDataSource collectionView:self numberOfItemsInSection:section];

}

- (NSUInteger)dataControllerNumberOfSections:(ASDataController *)dataController {

if ([_asyncDataSource respondsToSelector:@selector(numberOfSectionsInCollectionView:)]) {

return [_asyncDataSource numberOfSectionsInCollectionView:self];

} else {

return 1;

}

}

- (void)dataControllerLockDataSource

{

ASDisplayNodeAssert(!self.asyncDataSourceLocked, @"The data source has already been locked");

self.asyncDataSourceLocked = YES;

if ([_asyncDataSource respondsToSelector:@selector(collectionViewLockDataSource:)]) {

[_asyncDataSource collectionViewLockDataSource:self];

}

}

- (void)dataControllerUnlockDataSource

{

ASDisplayNodeAssert(self.asyncDataSourceLocked, @"The data source has already been unlocked");

self.asyncDataSourceLocked = NO;

if ([_asyncDataSource respondsToSelector:@selector(collectionViewUnlockDataSource:)]) {

[_asyncDataSource collectionViewUnlockDataSource:self];

}

}

#pragma mark -

#pragma mark ASRangeControllerDelegate.

- (void)rangeControllerBeginUpdates:(ASRangeController *)rangeController {

ASDisplayNodeAssertMainThread();

_performingBatchUpdates = YES;

}

- (void)rangeControllerEndUpdates:(ASRangeController *)rangeController completion:(void (^)(BOOL))completion {

ASDisplayNodeAssertMainThread();

[super performBatchUpdates:^{

[_batchUpdateBlocks enumerateObjectsUsingBlock:^(dispatch_block_t block, NSUInteger idx, BOOL *stop) {

block();

}];

} completion:^(BOOL finished) {

if (completion) {

completion(finished);

}

}];

[_batchUpdateBlocks removeAllObjects];

_performingBatchUpdates = NO;

}

- (NSArray *)rangeControllerVisibleNodeIndexPaths:(ASRangeController *)rangeController

{

ASDisplayNodeAssertMainThread();

return [self indexPathsForVisibleItems];

}

- (CGSize)rangeControllerViewportSize:(ASRangeController *)rangeController

{

ASDisplayNodeAssertMainThread();

return self.bounds.size;

}

- (NSArray *)rangeController:(ASRangeController *)rangeController nodesAtIndexPaths:(NSArray *)indexPaths

{

return [_dataController nodesAtIndexPaths:indexPaths];

}

- (void)rangeController:(ASRangeController *)rangeController didInsertNodesAtIndexPaths:(NSArray *)indexPaths withAnimationOption:(ASDataControllerAnimationOptions)animationOption

{

ASDisplayNodeAssertMainThread();

if (_performingBatchUpdates) {

[_batchUpdateBlocks addObject:^{

[super insertItemsAtIndexPaths:indexPaths];

}];

} else {

[UIView performWithoutAnimation:^{

[super insertItemsAtIndexPaths:indexPaths];

}];

}

}

- (void)rangeController:(ASRangeController *)rangeController didDeleteNodesAtIndexPaths:(NSArray *)indexPaths withAnimationOption:(ASDataControllerAnimationOptions)animationOption

{

ASDisplayNodeAssertMainThread();

if (_performingBatchUpdates) {

[_batchUpdateBlocks addObject:^{

[super deleteItemsAtIndexPaths:indexPaths];

}];

} else {

[UIView performWithoutAnimation:^{

[super deleteItemsAtIndexPaths:indexPaths];

}];

}

}

- (void)rangeController:(ASRangeController *)rangeController didInsertSectionsAtIndexSet:(NSIndexSet *)indexSet withAnimationOption:(ASDataControllerAnimationOptions)animationOption

{

ASDisplayNodeAssertMainThread();

if (_performingBatchUpdates) {

[_batchUpdateBlocks addObject:^{

[super insertSections:indexSet];

}];

} else {

[UIView performWithoutAnimation:^{

[super insertSections:indexSet];

}];

}

}

- (void)rangeController:(ASRangeController *)rangeController didDeleteSectionsAtIndexSet:(NSIndexSet *)indexSet withAnimationOption:(ASDataControllerAnimationOptions)animationOption

{

ASDisplayNodeAssertMainThread();

if (_performingBatchUpdates) {

[_batchUpdateBlocks addObject:^{

[super deleteSections:indexSet];

}];

} else {

[UIView performWithoutAnimation:^{

[super deleteSections:indexSet];

}];

}

}

@end