ALAssetsGroup详解

ALAssetsGroup类是系统用于映射相册资源中的每个相册，可以通过该类获取相册中的资源文件，并且能向相册中添加资源文件

    

    //保存图片到系统默认的相册中，使用cgimageref的形式，并且选择图片以什么旋转方向的形式保存，并返回照片的url地址

    /*
     typedef enum {
     ALAssetOrientationUp,            // default orientation
     ALAssetOrientationDown,          // 180 deg rotation
     ALAssetOrientationLeft,          // 90 deg CCW
     ALAssetOrientationRight,         // 90 deg CW
     ALAssetOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip
     ALAssetOrientationDownMirrored,  // horizontal flip
     ALAssetOrientationLeftMirrored,  // vertical flip
     ALAssetOrientationRightMirrored, // vertical flip
     } ALAssetOrientation;
     */
    UIImage* image = [UIImage imageNamed:@"test.png"];
    [_library writeImageToSavedPhotosAlbum:[image CGImage] orientation:ALAssetOrientationLeft completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"save image:%@",assetURL);
        //通过ALAssetsLibrary迭代取出所有相册
        [_library enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
            NSString* groupname = [group valueForProperty:ALAssetsGroupPropertyName];
            //如果相册的名称是test的时候，对其进行操作
            if ([groupname isEqualToString:@"test"]) {
                //设置相册组的筛选条件，ALAssetsFilter类表示筛选条件，allPhotos代表相册只包含相片，allVideos代表只包含视频，allAssets代表包含所有资源
                [group setAssetsFilter:[ALAssetsFilter allPhotos]];
                //通过刚保存的照片的url，把保存到默认相册的照片也保存到test相册中
                [_library assetForURL:assetURL resultBlock:^(ALAsset *asset) {
                    //添加资源到指定的相册
                    [group addAsset:asset];
                    //获取相册中一共的资源数量
                    int count = [group numberOfAssets];
                    NSLog(@"count:%d",count);
                    dispatch_queue_t main = dispatch_get_main_queue();
                    dispatch_async(main, ^{
                        //获取相册的封面图片
                        CGImageRef poster = [group posterImage];
                        [imageView setImage:[UIImage imageWithCGImage:poster]];
                    });
                    //NSString *const ALAssetsGroupPropertyName;
                    //NSString *const ALAssetsGroupPropertyType;
                    //NSString *const ALAssetsGroupPropertyPersistentID;
                    //NSString *const ALAssetsGroupPropertyURL;
                    //查看相册的名字
                    NSLog(@"ALAssetsGroupPropertyName:%@",[group valueForProperty:ALAssetsGroupPropertyName]);
                    //查看相册的类型
                    NSLog(@"ALAssetsGroupPropertyType:%@",[group valueForProperty:ALAssetsGroupPropertyType]);
                    //查看相册的存储id
                    NSLog(@"ALAssetsGroupPropertyPersistentID:%@",[group valueForProperty:ALAssetsGroupPropertyPersistentID]);
                    //查看相册存储的位置地址
                    NSLog(@"ALAssetsGroupPropertyURL:%@",[group valueForProperty:ALAssetsGroupPropertyURL]);
                    //按遍历顺序获取指定索引的资源，遍历顺序可以是先序或倒序
                    /*
                     enum {
                     NSEnumerationConcurrent = (1UL << 0),
                     NSEnumerationReverse = (1UL << 1),
                     };
                     typedef NSUInteger NSEnumerationOptions;
                     */
                    [group enumerateAssetsAtIndexes:[NSIndexSet indexSetWithIndex:0] options:NSEnumerationConcurrent usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                    //按顺便遍历获取相册中所有的资源，index代表资源的索引，stop赋值为false时，会停止遍历
                    [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                     //按顺便遍历获取相册中所有的资源，遍历顺序可以是先序或倒序，index代表资源的索引，stop赋值为false时，会停止遍历
                    [group enumerateAssetsWithOptions:NSEnumerationReverse usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                        
                    }];
                    
                } failureBlock:^(NSError *error) {
                    
                }];
            }
        } failureBlock:^(NSError *error) {
            
        }];
    }];