Question

我正在使用PhotoKit从系统相册中提取照片并将其放入UICollectionView。

对于UICollectionViewCell，我设置如下：

cell.imageView.contentMode = UIViewContentModeScaleAspectFill;

在初始化UICollectionView时，我仅从PHAsset：collection获取照片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];
    }
}];

然后我从上方UIImage请求PHFetchResult，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;
}

但是当我运行它并快速滚动UICollectionView时，我发现内存使用变得如此陡峭：

如果在内存不足时会崩溃，我该如何减少它？

Answer 1

我现在所做的是

减少已提取的PHAsset个对象的目标大小;

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，顶部内存也会小于50 MB，并且感谢Caching（我猜它基于我的代码工作）它没有＆＃39; t波动那么多，内存使用是这样的：

<强>更新根据另一篇文章here，建议不要指定PHImageRequestOptions个对象。相反，您可以将它留给iOS来决定哪种方式能够以最佳质量和最短时间呈现照片。

Answer 2

我建议看看我提到的答案here。这不仅可以帮助您进行缓存，而且Apple提供的Photos Framework示例可以帮助您解决任何问题。

如何使用PhotoKit减少内存使用？

2 个答案: