面试：ios 批量上传图片

/**批量上传图片*/
+ (NSURLSessionUploadTask*)uploadTaskWithImage:(UIImage*)image completion:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionBlock {
    // 构造 NSURLRequest
    NSError* error = NULL;
    NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:[NSString stringWithFormat:@"%@%@",JHTestUrl,JHPostImageFileURL] parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        NSData* imageData = UIImageJPEGRepresentation(image, 1.0);
        [formData appendPartWithFileData:imageData name:@"file1" fileName:@"someFileName.png" mimeType:@"image/png"];
    } error:&error];
    // 将 NSURLRequest 与 completionBlock 包装为 NSURLSessionUploadTask
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    NSURLSessionUploadTask *uploadTask = [manager uploadTaskWithStreamedRequest:request progress:^(NSProgress * _Nonnull uploadProgress) {
    } completionHandler:completionBlock];
    return uploadTask;
}

/**
 *  批量上传图片的处理方法(GCD)
 *
 *  @param images     要上传的图片数组
 *  @param completion 上传完成之后的正确返回路径
 */
+(void)uploadImagesWithImages:(NSArray <UIImage *>*)images completion:(void(^)(NSMutableArray *successResultPath))completion{
    // 准备保存结果的数组，元素个数与上传的图片个数相同，先用 NSNull 占位
    NSMutableArray* result = [NSMutableArray array];
    for (NSInteger i = 0; i<images.count; i++) {
        [result addObject:[NSNull null]];
    }
    dispatch_group_t group = dispatch_group_create();
    for (NSInteger i = 0; i < images.count; i++) {
        dispatch_group_enter(group);
        NSURLSessionUploadTask* uploadTask = [self uploadTaskWithImage:images[i] completion:^(NSURLResponse *response, NSDictionary* responseObject, NSError *error) {
            if (error) {
                //NSLog(@"第 %d 张图片上传失败: %@", (int)i + 1, error);
                dispatch_group_leave(group);
            } else {
               // NSLog(@"第 %d 张图片上传成功: %@", (int)i + 1, responseObject);
                @synchronized (result) {
                /**NSMutableArray 是线程不安全的，所以加个同步锁*/
                    result[i] = responseObject;
                }
                dispatch_group_leave(group);
            }
        }];
        [uploadTask resume];
    }
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        if (completion) {
            completion(result);
        }
    });
}