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.");                                        }];             });