Swift Alamofire 多请求DispatchGroup

        let group = DispatchGroup()//创建
        for i in 0..<10{
            group.enter()//加入组
             Alamofire.request(urlstring, method:.post).responseJSON { (returnResult) in
                    group.leave()//离开组
           }
         }

        group.notify(queue: DispatchQueue.main) {
              //请求全部完毕
        }