System.Net.Sockets.UdpClient.SendAsync C# (CSharp) Method

        public Task<int> SendAsync(byte[] datagram, int bytes)
        {
            return Task<int>.Factory.FromAsync(
                (targetDatagram, targetBytes, callback, state) => ((UdpClient)state).BeginSend(targetDatagram, targetBytes, callback, state),
                asyncResult => ((UdpClient)asyncResult.AsyncState).EndSend(asyncResult),
                datagram,
                bytes,
                state: this);
        }

        /// <summary>
        /// 向客户端异步发送文件
        /// </summary>
        /// <param name="ip"></param>
        /// <param name="port"></param>
        /// <param name="filePath"></param>
        public async Task SendToClientFileAsync(string ip, int port, string filePath, Message msg)
        {
            // 新建 Udp 用于发送文件
            var sendClient = new UdpClient();

            try
            {
                FileInfo fileInfo = new FileInfo(filePath);
                msg.Type = MessageEnum.FILE;  // 设置发送文件标识
                msg.FileLength = fileInfo.Length;

                msg.FileName = Regex.Match(filePath, @"\\([^\\]+\.[^\\]+)").Groups[1].Value;  // 获取文件名

                byte[] datagram = Encoding.Unicode.GetBytes(JsonConvert.SerializeObject(msg));
                IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse(ip), port);

                /*
                 * 向‘原’远程客户端发送请求传送文件的请求,
                 * 接收‘新’远程客户端的响应,获取传送文件的端口
                 * 
                 * 注：原远程客户端用于发送消息，新远程客户端用于发送文件
                 */
                await sendClient.SendAsync(datagram, datagram.Length, endPoint);

                //IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
                UdpReceiveResult result = await sendClient.ReceiveAsync().ConfigureAwait(false);   // 阻塞直到接收到远程客户端的响应

                /*
                 * 开始发送文件
                 */
                byte[] buffer = new byte[MAXSIZE];
                using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, 1, true))
                {
                    int percent = 0;
                    int count = 0;
                    while ((count = await fs.ReadAsync(buffer, 0, buffer.Length).ConfigureAwait(false)) > 0)
                    {
                        //await Task.Delay(10);
                        await sendClient.SendAsync(buffer, count, result.RemoteEndPoint);

                        if (Client.SendFileProgressNotify != null)
                        {
                            Client.SendFileProgressNotify(String.Format("{0:F2}%", (percent += count) / msg.FileLength * 100));
                        }
                    }
                    sendClient.Close();
                }
            }
            catch (Exception e)
            {
                Log.Write(e.Message);
            }
        }