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.");

                                        }];

    });