照片保存到相册，并添加到自定义相册中

-(void)addAssetURL:(NSURL*)assetURL toAlbum:(NSString*)albumName withCompletionBlock:(SaveImageCompletion)completionBlock
{
    //相册存在标示
    __block BOOL albumWasFound = NO;

    ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc] init];
    //search all photo albums in the library
    [assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAlbum usingBlock:^(ALAssetsGroup *group, BOOL *stop)
     {

         //判断相册是否存在
         if ([albumName compare: [group valueForProperty:ALAssetsGroupPropertyName]]==NSOrderedSame) {

             //存在
             albumWasFound = YES;

             //get a hold of the photo's asset instance
             [assetsLibrary assetForURL: assetURL
                            resultBlock:^(ALAsset *asset) {

                                //add photo to the target album
                                [group addAsset: asset];

                                //run the completion block
                                completionBlock(nil);

                            } failureBlock: completionBlock];
             return;
         }

         //如果不存在该相册创建
         if (group==nil && albumWasFound==NO)
         {
             __weak ALAssetsLibrary* weakSelf = assetsLibrary;

             //创建相册
             [assetsLibrary addAssetsGroupAlbumWithName:albumName resultBlock:^(ALAssetsGroup *group)
              {

                  //get the photo's instance
                  [weakSelf assetForURL: assetURL
                            resultBlock:^(ALAsset *asset)
                   {

                       //add photo to the newly created album
                       [group addAsset: asset];

                       //call the completion block
                       completionBlock(nil);

                   } failureBlock: completionBlock];

              } failureBlock: completionBlock];
             return;
         }

     }failureBlock:completionBlock];
}

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