如何将图片保存至自定义分组

       一般我们照片存储都是直接存储在相机胶卷中，调用下面的方法就可以了：

void UIImageWriteToSavedPhotosAlbum (
   UIImage  *image,
   id       completionTarget,
   SEL      completionSelector,
   void     *contextInfo
);

       但是如果我们想将图片存储到自定义的分组该怎么做呢，我查了一下ALAssetsLibrary的文档，发现没有相应的方法，好吧，google一下，发现了一篇文章：点击打开链接。

       作者的解决思路如下：

1.将图片先保存到相机胶卷中；

2.在相机胶卷中找到这个图片所创建的AlAsset；

3.将此AlAsset添加到你需要存放的自定义分组中。

      主要代码如下所示，注释也很清楚了：

-(void)saveImage:(UIImage*)image toAlbum:(NSString*)albumName withCompletionBlock:(SaveImageCompletion)completionBlock
{
    //write the image data to the assets library (camera roll)
    [self writeImageToSavedPhotosAlbum:image.CGImage orientation:(ALAssetOrientation)image.imageOrientation 
                        completionBlock:^(NSURL* assetURL, NSError* error) {
                              
                          //error handling
                          if (error!=nil) {
                              completionBlock(error);
                              return;
                          }

                          //add the asset to the custom photo album
                          [self addAssetURL: assetURL 
                                    toAlbum:albumName 
                        withCompletionBlock:completionBlock];
                          
                      }];
}

-(void)addAssetURL:(NSURL*)assetURL toAlbum:(NSString*)albumName withCompletionBlock:(SaveImageCompletion)completionBlock
{
    __block BOOL albumWasFound = NO;
    
    //search all photo albums in the library
    [self enumerateGroupsWithTypes:ALAssetsGroupAlbum 
                        usingBlock:^(ALAssetsGroup *group, BOOL *stop) {

                            //compare the names of the albums
                            if ([albumName compare: [group valueForProperty:ALAssetsGroupPropertyName]]==NSOrderedSame) {
                                
                                //target album is found
                                albumWasFound = YES;
                                
                                //get a hold of the photo's asset instance
                                [self assetForURL: assetURL 
                                      resultBlock:^(ALAsset *asset) {
                                                  
                                          //add photo to the target album
                                          [group addAsset: asset];
                                          
                                          //run the completion block
                                          completionBlock(nil);
                                          
                                      } failureBlock: completionBlock];

                                //album was found, bail out of the method
                                return;
                            }
                            
                            if (group==nil && albumWasFound==NO) {
                                //photo albums are over, target album does not exist, thus create it
                                
                                __weak ALAssetsLibrary* weakSelf = self;

                                //create new assets album
                                [self 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];

                                //should be the last iteration anyway, but just in case
                                return;
                            }
                            
                        } failureBlock: completionBlock];
}

           作者写了一个小demo：CustomAlbumDemo.zip 上面的代码用到了ARC，如果你的工程没有使用ARC，记得做相应处理。

      如何添加分组：

            [[DataCenter defaultAssetsLibrary] addAssetsGroupAlbumWithName:[alertView textFieldAtIndex:0].text
                                                               resultBlock:resulBlock
                                                              failureBlock:nil];