IOS获取相册照片的大小

     ALAssetsLibrary *alLibrary = [[ALAssetsLibrary alloc] init];

        __block float fileMB  = 0.0;

        [alLibrary assetForURL:[NSURL URLWithString:imgURL] resultBlock:^(ALAsset *asset) {

            ALAssetRepresentation *representation = [asset defaultRepresentation];

            fileMB = (float)([representation size]/HQKBTransformToMBCount);

            NSLog(@"图片大小=%fkb", fileMB);

        } failureBlock:^(NSError *error) {

        }];