ios - 无法使用 PhotoKit 获得从相册请求的清晰图像

Question

我正在使用 PhotoKit 来获取其中一个系统相册中的照片，如下所示:

PHFetchOptions *fetchOptions = [[PHFetchOptions alloc] init];
fetchOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:YES]];
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"]) {
        PHFetchResult *photos = [PHAsset fetchAssetsInAssetCollection:collection options:nil];
        NSLog(@"PHOTOS: %ld", photos.count);
        _photos = nil;
        _photos = @[].mutableCopy;
        for (PHAsset *asset in photos) {
            [self loadImageFromPHAsset:asset];
        }
    }
}];

然后在我的自定义辅助方法中:(void)loadImageFromPHAsset:(PHAsset *)asset，我有这个:

-(void)loadImageFromPHAsset:(PHAsset *)asset
{
    PHImageManager *manager = [PHImageManager defaultManager];
    CGSize targetSize = _layout.itemSize;
    [manager requestImageForAsset:asset targetSize:targetSize contentMode:PHImageContentModeAspectFill options:nil resultHandler:^(UIImage *result, NSDictionary *info) {
        [_photos addObject:result];
    }];
    [self.collectionView reloadData];
}

所以我有一组图像，我将它们呈现在我的 UICollectionViewCell 中:

UIImage *image = [_photos objectAtIndex:indexPath.row];
cell.imageView.contentMode = UIViewContentModeScaleAspectFill;
cell.imageView.image = image;

但是我得到的是这样的，很模糊，怎么才能看清楚呢？

Answer 1

首先 targetSize 应该乘以 scale 来计算屏幕的比例，这样

CGFloat scale = [UIScreen mainScreen].scale;
CGSize targetSize = CGSizeMake(_layout.itemSize.width*scale, _layout.itemSize.height*scale);

其次，尝试这些选项以获得精确尺寸的图像，

//Async call returned on main thread, can return multiple times
        
PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
options.resizeMode = PHImageRequestOptionsResizeModeExact;

最后，如果你有性能问题，使用PHCachingManager，我已经回答了关于性能改进的问题here

希望对你有帮助。

编辑:

我没有意识到图像是存储在数组中的。尝试在图像选项中设置同步标志。

PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
options.synchronous = YES;
options.resizeMode = PHImageRequestOptionsResizeModeExact;