ios - 如何减少 PhotoKit 的内存使用？

Question

我正在使用 PhotoKit 从系统相册中获取照片并将它们放入 UICollectionView 中。

1. 对于 UICollectionViewCell，我这样设置:

   cell.imageView.contentMode = UIViewContentModeScaleAspectFill;
   

2. 初始化我的 UICollectionView 时，我从 collection 中获取照片 PHAsset:仅 Camera Roll :

   PHFetchResult *fetchResult = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
   [fetchResult enumerateObjectsUsingBlock:^(PHAssetCollection *collection, NSUInteger idx, BOOL *stop) {
       NSLog(@"ALBUM NAME: %@", collection.localizedTitle);
       if ([collection.localizedTitle isEqualToString:@"Camera Roll"]) {
           _fetchedPhotos = [PHAsset fetchAssetsInAssetCollection:collection options:nil];
           _pickedStatuses = @[].mutableCopy;            
   
           NSMutableArray *assets = @[].mutableCopy;
   
           _manager = [[PHCachingImageManager alloc] init];
           _options = [[PHImageRequestOptions alloc] init];
           _options.resizeMode = PHImageRequestOptionsResizeModeExact;
           _options.deliveryMode = PHImageRequestOptionsDeliveryModeOpportunistic;
   
           CGFloat scale = [UIScreen mainScreen].scale;
           CGSize targetSize = CGSizeMake(layout.itemSize.width*scale, layout.itemSize.height*scale);
   
           //I'm not sure if this api should be called here
           [_manager startCachingImagesForAssets:assets targetSize:targetSize contentMode:PHImageContentModeAspectFill options:_options];
       }
   }];
   

3. 然后我从上面的 PHFetchResult 请求 UIImage，如下所示:

   -(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
   {
       MYCell *cell = (MYCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"reuseCell" forIndexPath:indexPath];
   
       CGFloat scale = [UIScreen mainScreen].scale;
       CGSize targetSize = CGSizeMake(_layout.itemSize.width*scale, _layout.itemSize.height*scale);
   
       PHAsset *asset = _fetchedPhotos[indexPath.item];
       [_manager requestImageForAsset:asset targetSize:targetSize contentMode:PHImageContentModeAspectFill options:_options resultHandler:^(UIImage *result, NSDictionary *info) {
            cell.imageView.image = result;
       }];
   
       return cell;
   }
   

但是当我运行它并足够快地滚动 UICollectionView 时，我发现内存使用变得像这样陡峭:

如果内存不足会崩溃，如何减少它？

Answer 1

我现在做的是

1. 减少获取的PHAsset对象的目标大小；

2. 尝试采用缓存。我的代码如下:

   CGFloat scale = 1.5; //or an even smaller one
   if (!_manager) {
       _manager = [[PHCachingImageManager alloc] init];
   }
   if (!_options) {
       _options = [[PHImageRequestOptions alloc] init];
   }
   _options.resizeMode = PHImageRequestOptionsResizeModeExact;
   _options.deliveryMode = PHImageRequestOptionsDeliveryModeOpportunistic;
   
   NSRange range = NSMakeRange(0, _fetchedPhotos.count);
   NSIndexSet *set = [NSIndexSet indexSetWithIndexesInRange:range];
   NSArray *assets = [_fetchedPhotos objectsAtIndexes:set];
   
   CGSize targetSize = CGSizeMake(_layout.itemSize.width*scale, _layout.itemSize.height*scale);
   
   [_manager startCachingImagesForAssets:assets targetSize:targetSize contentMode:PHImageContentModeAspectFill options:_options];
   

现在，即使我足够快地滚动 UICollectionView，顶部内存也不会超过 50 MB，这要归功于 Caching(我猜它基于我的代码工作)它没有那么大的波动，内存使用是这样的:

更新根据另一篇文章 here , 建议不要指定 PHImageRequestOptions 对象。相反，您可以将它留给 iOS 来决定什么是最适合您的，以最好的质量和最短的时间呈现照片。