ios - 如何使用 PhotoKit 减少内存使用？

Question

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

1. 对于UICollectionViewCell，我这样设置：

   cell.imageView.contentMode = UIViewContentModeScaleAspectFill;
   

2. 初始化 my 时，我仅从:UICollectionView获取照片：PHAssetcollectionCamera 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. UIImage然后我像这样从PHFetchResult上面请求：

   -(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;
   }
   

但是当我运行它并以足够快的速度滚动时UICollectionView，我发现内存使用变得像这样陡峭：

如果内存不足时它会崩溃，我该如何减少它？

Answer 1

我现在所做的是

1. 减小获取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];
   

现在即使我滚动UICollectionView得足够快，顶部内存也会小于50 MB，并且由于Caching（我猜它是基于我的代码工作的）它不会波动太大，内存使用是这样的：

更新 根据这里的另一篇文章，建议不要指定PHImageRequestOptions对象。相反，您可以将其留给 iOS 来决定最适合您以最好的质量和最少的时间呈现照片。

Answer 2

我建议看看我在这里提到的答案。这不仅可以帮助您进行缓存，而且苹果的照片框架示例可以帮助您解决任何问题。