ALAssetsLibrary使用

self.assetsLibrary = [[ALAssetsLibrary alloc] init];
    dispatch_queue_t dispatchQueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(dispatchQueue, ^(void) {
        // 遍历所有相册
        [self.assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll
                                          usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
                                              // 遍历每个相册中的项ALAsset
                                              [group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index,BOOL *stop) {
                                                   
                                                  __block BOOL foundThePhoto = NO;
                                                  if (foundThePhoto){
                                                      *stop = YES;
                                                  }
                                                  // ALAsset的类型
                                                  NSString *assetType = [result valueForProperty:ALAssetPropertyType];
                                                  if ([assetType isEqualToString:ALAssetTypePhoto]){
                                                      foundThePhoto = YES;
                                                      *stop = YES;
                                                      ALAssetRepresentation *assetRepresentation =[result defaultRepresentation];
                                                      CGFloat imageScale = [assetRepresentation scale];
                                                      UIImageOrientation imageOrientation = (UIImageOrientation)[assetRepresentation orientation];
                                                      dispatch_async(dispatch_get_main_queue(), ^(void) {
                                                          CGImageRef imageReference = [assetRepresentation fullResolutionImage];
                                                          // 对找到的图片进行操作
                                                          UIImage *image =[[UIImage alloc] initWithCGImage:imageReference scale:imageScale orientation:imageOrientation];
                                                          if (image != nil){
                                                              //获取到第一张图片
                                                          } else {
                                                              NSLog(@"Failed to create the image.");
                                                          } });
                                                  }
                                              }];
                                          }
                                        failureBlock:^(NSError *error) {
                                            NSLog(@"Failed to enumerate the asset groups.");
                                        }];
         
    });