传智播客视频里的手写聊天室C# SaveFileDialog调用了show但不跳出来

希望同看传智播客视频的朋友给我答疑解惑啊
就是客户端向服务端发送文件的时候
当收个比特数组为1就是文件传输假设客户端发的是向服务端发文件
下面是服务端代码接受方法
新起一个线程 传入套接字sok
为1文件传输
注释两行应该会跳出保存窗口的但是怎么不跳出呢  void rec(object sok)
        {
            while (true)
            {
                Socket warch = (Socket)sok;
                byte[] ar = new byte[1024 * 1014 * 2];
                int length = warch.Receive(ar);
                
                if (ar[0] == 0)
                {
                    OpenFileDialog ofd = new OpenFileDialog();
                    ofd.ShowDialog(); 
                    string c = System.Text.Encoding.UTF8.GetString(ar, 1, length - 1);
                    mess(c);
                }
                else if (ar[0] == 1)
                {
                   
                                      //SaveFileDialog sfd = new SaveFileDialog();
                    
                    //if (sfd.ShowDialog() == DialogResult.OK)
                    {
                        string st = sfd.FileName;
                        using (FileStream sss = new FileStream(st, FileMode.Create, FileAccess.Write))
                        {
                            sss.Write(ar, 1, length - 1);
                            mess("ok" + st);                        }
                    }
                }