//设置文件路径
NSString *folder = @"xxx" ;
//创建文件夹
[FileUtils createFolderIfNotExist:folder];
//获取沙盒路径并且拼接文件路径
NSString *documentsDirectory= [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
NSString *fileName = [NSString stringWithFormat:@"xxx"];
NSString *path = [folder stringByAppendingString:文件名];
NSString *realPath = [documentsDirectory stringByAppendingString:path];
//存总数据
NSFileManager *fileManager = [NSFileManager defaultManager];
[fileManager createFileAtPath: realPath contents:文件数据 attributes:nil];

uint32_t point = 0; //移动指针
double offset = 300*1024; //偏移量300kb
double trunkCountFloat = fileDataLength/offset; //分片块数
uint32_t trunkCount = trunkCountFloat; //求出浮点型片数

if (fileDataLength <= offset) { //只有一片
  //插入数据库列表
}

for(NSUInteger i = 0; i<trunkCount; i++)
  {
  NSData *trunkdata ;
  if (i == (trunkCount-1)){ //最后一片
    trunkdata = [fileData subdataWithRange:NSMakeRange(point, fileDataLength -point)];  
  }else{
    trunkdata = [fileData subdataWithRange:NSMakeRange(point, offset)]; 
  }
  }

point += offset;

[fileManager createFileAtPath:分片数据路径 contents:分片数据 attributes:nil];
//插入数据库
  ...

//拼接数据表单
NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST" URLString:urlStr parameters:dic constructingBodyWithBlock:^(id<AFMultipartFormData > formData) {   
  [formData appendPartWithFileData:txt文件数据 name:字段 fileName:txt文件名 mimeType:@"text"];
  } error:&error];  
  if (error) {   
   DLog(@"拼接表单失败");
  }
  //上传
  AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];  manager.operationQueue.maxConcurrentOperationCount = 1;
  manager.responseSerializer = [AFJSONResponseSerializer serializer];
  NSURLSessionUploadTask *uploadTask;
  uploadTask = [manager      uploadTaskWithStreamedRequest:request
      progress:^(NSProgress * _Nonnull uploadProgress) {       
      }completionHandler:^(NSURLResponse * _Nonnull response, id _Nullable responseObject, NSError * _Nullable error) {
       //成功的回调
       complete(jsonBackDic); 
       //失败的回调
       fail(error.localizedDescription,error.code);    
      }];
  //最后一定要写上这句代码启动
  [uploadTask resume];