项目中经常遇到多图片的上传需求，这个多文件上传的方法可以使用AFN中的一个方法，
AFNetWorking的作者在GitHub的介绍中列出了这个方法：

Creating an Upload Task for a Multi-Part Request, with Progress

NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:@"http://example.com/upload" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        [formData appendPartWithFileURL:[NSURL fileURLWithPath:@"file://path/to/image.jpg"] name:@"file" fileName:@"filename.jpg" mimeType:@"image/jpeg" error:nil];
    } error:nil];

AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

NSURLSessionUploadTask *uploadTask;
uploadTask = [manager
              uploadTaskWithStreamedRequest:request
              progress:^(NSProgress * _Nonnull uploadProgress) {
                  // This is not called back on the main queue.
                  // You are responsible for dispatching to the main queue for UI updates
                  dispatch_async(dispatch_get_main_queue(), ^{
                      //Update the progress view
                      [progressView setProgress:uploadProgress.fractionCompleted];
                  });
              }
              completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
                  if (error) {
                      NSLog(@"Error: %@", error);
                  } else {
                      NSLog(@"%@ %@", response, responseObject);
                  }
              }];

[uploadTask resume];

具体可以参照源码注释看下AFNetWorking作者的解释。

下面把结合我们业务的代码拿出来，说一下我们做多图片上传时的思路。
大体说一下：多个图片组合成数组，以uploadKeys区分每个图片，结合参数转成data添加到formData中创建任务请求，再将任务请求以数据流的形式上传。

- (void)uploadPhotoWithDataSource:(NSArray *)uploadDataSource parametersDic:(NSDictionary *)parametersDic uploadURI:(NSString *)uploadURI uploadKeys:(NSArray *)uploadKeys uploadMethod:(NSString *)uploadMethod uploadSingleSuccess:(YHShopkeeperUploadPhotoSuccess)uploadSingleSuccess allPhotosProgress:(YHShopkeeperUploadProgress)progress allRequestSucess:(YHShopkeeperAllUploadPhotoRequestSuccess)successBlock requestFailed:(YHShopkeeperAllUploadPhototRequestFailure)failedBlock
{
    // 创建会话管理
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    
    NSString *token = [[NSUserDefaults standardUserDefaults] objectForKey:accessTokeKey];
    
    // uploadURI为图片上传的地址
    NSString *jsonStr = [self requireParameters:parametersDic uri:uploadURI requestParams:nil needRandom:NO];
    NSString *urlStr = [NSString stringWithFormat:@"%@%@?access_token=%@&json=%@",BASE_URL,RESOURCES_URL,token,[jsonStr stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]]];
    
    // 创建多任务请求
    // uploadMethod为上传方式，此处应为“POST”
    NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:uploadMethod URLString:urlStr parameters:@{@"json" : jsonStr} constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        
        // 多图片，所以使用for循环把每个图片转成NSData的形式添加到formData
        for (int i = 0; i<uploadDataSource.count; i++) {
            
            UIImage *image = uploadDataSource[i];
            
            // 使用时间给每个图片命名
            // 1) 创建data对象
            NSDate *date = [NSDate date];
            // 2) 使用日期格式化工具
            NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
            // 3) 指定日期格式
            [formatter setDateFormat:@"yyyyMMddHHmmss"];
            NSString *dateStr = [formatter stringFromDate:date];
            // 4) 使用系统时间生成一个文件名
            NSString *fileName = [NSString stringWithFormat:@"%@.png", dateStr];
            
            // 压缩图片
            NSData *data = UIImageJPEGRepresentation(image, 1);
            if (data.length>100*1024) {
                if (data.length>1024*1024) {//1M以及以上
                    data=UIImageJPEGRepresentation(image, 0.1);
                }else if (data.length>512*1024) {//0.5M-1M
                    data=UIImageJPEGRepresentation(image, 0.5);
                }else if (data.length>200*1024) {//0.25M-0.5M
                    data=UIImageJPEGRepresentation(image, 0.9);
                }
            }

            // uploadKeys为一个数组，存放的是不同图片的路径，后台以路径判别是哪个图片
            [formData appendPartWithFileData:data name:uploadKeys[i] fileName:fileName mimeType:@"image/jpeg"];
        }
    } error:nil];

    
    // 创建上传会话任务
    NSURLSessionUploadTask *uploadTask = [manager uploadTaskWithStreamedRequest:request progress:^(NSProgress * _Nonnull uploadProgress) {
        
        // 进度回调
        if (progress) {
            progress(uploadProgress);
        }
        
    } completionHandler:^(NSURLResponse * _Nonnull response, id  _Nullable responseObject, NSError * _Nullable error) {
        
        // 错误回调
        if (responseObject[@"errMsg"] || error || !responseObject)
        {
            if (failedBlock)
            {
                failedBlock(error,responseObject[@"errMsg"]);
            }
        }
        else
        {
            // 成功回调
            if (successBlock) {
                successBlock(responseObject);
            }
        }
        
        [manager invalidateSessionCancelingTasks:NO];
    }];
    
    [uploadTask resume];
}