这是在 UICollectionView 中显示“视频墙”的有效解决方案：
1) 将所有单元格存储在 NSMapTable 中（从今以后，您将只能从 NSMapTable 访问单元格对象）：
self.cellCache = [[NSMapTable alloc] initWithKeyOptions:NSPointerFunctionsWeakMemory valueOptions:NSPointerFunctionsStrongMemory capacity:AppDelegate.sharedAppDelegate.assetsFetchResults.count];
for (NSInteger i = 0; i < AppDelegate.sharedAppDelegate.assetsFetchResults.count; i++) {
[self.cellCache setObject:(AssetPickerCollectionViewCell *)[self.collectionView dequeueReusableCellWithReuseIdentifier:CellReuseIdentifier forIndexPath:[NSIndexPath indexPathForItem:i inSection:0]] forKey:[NSIndexPath indexPathForItem:i inSection:0]];
}
2) 将此方法添加到您的 UICollectionViewCell 子类中：
- (void)setupPlayer:(PHAsset *)phAsset {
typedef void (^player) (void);
player play = ^{
NSString __autoreleasing *serialDispatchCellQueueDescription = ([NSString stringWithFormat:@"%@ serial cell queue", self]);
dispatch_queue_t __autoreleasing serialDispatchCellQueue = dispatch_queue_create([serialDispatchCellQueueDescription UTF8String], DISPATCH_QUEUE_SERIAL);
dispatch_async(serialDispatchCellQueue, ^{
__weak typeof(self) weakSelf = self;
__weak typeof(PHAsset) *weakPhAsset = phAsset;
[[PHImageManager defaultManager] requestPlayerItemForVideo:weakPhAsset options:nil
resultHandler:^(AVPlayerItem * _Nullable playerItem, NSDictionary * _Nullable info) {
if(![[info objectForKey:PHImageResultIsInCloudKey] boolValue]) {
AVPlayer __autoreleasing *player = [AVPlayer playerWithPlayerItem:playerItem];
__block typeof(AVPlayerLayer) *weakPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:player];
[weakPlayerLayer setFrame:weakSelf.contentView.bounds]; //CGRectMake(self.contentView.bounds.origin.x, self.contentView.bounds.origin.y, [[UIScreen mainScreen] bounds].size.width, [[UIScreen mainScreen] bounds].size.height * (9.0/16.0))];
[weakPlayerLayer setVideoGravity:AVLayerVideoGravityResizeAspect];
[weakPlayerLayer setBorderWidth:0.25f];
[weakPlayerLayer setBorderColor:[UIColor whiteColor].CGColor];
[player play];
dispatch_async(dispatch_get_main_queue(), ^{
[weakSelf.contentView.layer addSublayer:weakPlayerLayer];
});
}
}];
});
}; play();
}
3) 以这种方式从您的 UICollectionView 委托调用上述方法：
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
if ([[self.cellCache objectForKey:indexPath] isKindOfClass:[AssetPickerCollectionViewCell class]])
[self.cellCache setObject:(AssetPickerCollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellReuseIdentifier forIndexPath:indexPath] forKey:indexPath];
dispatch_async(dispatch_get_global_queue(0, DISPATCH_QUEUE_PRIORITY_HIGH), ^{
NSInvocationOperation *invOp = [[NSInvocationOperation alloc]
initWithTarget:(AssetPickerCollectionViewCell *)[self.cellCache objectForKey:indexPath]
selector:@selector(setupPlayer:) object:AppDelegate.sharedAppDelegate.assetsFetchResults[indexPath.item]];
[[NSOperationQueue mainQueue] addOperation:invOp];
});
return (AssetPickerCollectionViewCell *)[self.cellCache objectForKey:indexPath];
}
顺便说一下，下面是您将如何使用“照片”应用的“视频”文件夹中的所有视频填充 PHFetchResult 集合：
// Collect all videos in the Videos folder of the Photos app
- (PHFetchResult *)assetsFetchResults {
__block PHFetchResult *i = self->_assetsFetchResults;
if (!i) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
PHFetchResult *smartAlbums = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeSmartAlbumVideos options:nil];
PHAssetCollection *collection = smartAlbums.firstObject;
if (![collection isKindOfClass:[PHAssetCollection class]]) collection = nil;
PHFetchOptions *allPhotosOptions = [[PHFetchOptions alloc] init];
allPhotosOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:NO]];
i = [PHAsset fetchAssetsInAssetCollection:collection options:allPhotosOptions];
self->_assetsFetchResults = i;
});
}
NSLog(@"assetsFetchResults (%ld)", self->_assetsFetchResults.count);
return i;
}
如果您想过滤本地（而不是 iCloud）视频，这是我的假设，因为您正在寻找平滑滚动：
// Filter videos that are stored in iCloud
- (NSArray *)phAssets {
NSMutableArray *assets = [NSMutableArray arrayWithCapacity:self.assetsFetchResults.count];
[[self assetsFetchResults] enumerateObjectsUsingBlock:^(PHAsset *asset, NSUInteger idx, BOOL *stop) {
if (asset.sourceType == PHAssetSourceTypeUserLibrary)
[assets addObject:asset];
}];
return [NSArray arrayWithArray:(NSArray *)assets];
}