c# - 为什么只有在抛出异常后才更新表单

Question

我正在开发一个主要涉及Xbee和PC之间的COM端口通信的winform程序。请允许我先向您展示问题：

笔记：

1. 不用担心委托函数，它只是检查返回的字节

2. 该程序以前可以运行，我今天刚刚添加了高速设置。所以对于 xbee 设备，我必须以 9600 速度开始，然后更改为我需要的任何速度，即 38400。但是，一旦我将其设置为 38400，无需重启 xbee。下次连接设备时，速度保持@38400。这就是我添加尝试与另一个波特率连接的 if(initial_fail) 块的原因。

3. 请按照我用数字标记的评论

       try
       {
           portBuffer.Clear();
           myComPort.Write(myxbee.myxbee_cmd.cmd_mode, 0, myxbee.myxbee_cmd.cmd_mode.Length);   //RETURN OK <CR> 
   
           IAsyncResult res = d.BeginInvoke(null, null);
           if (res.IsCompleted == false)
           {
               res.AsyncWaitHandle.WaitOne(2000, false);
               if (res.IsCompleted == false)
                   initial_fail = 1; //1. start from here, once there is a timeout, set the initial_fail to 1, Time-out because the baudrate is not sync
                if (d.EndInvoke(res) == false)
                  throw new Exception("Failing to enter the cmd mode");
           }
       }
       catch (ApplicationException e)
       {
           MessageBox.Show(e.Message);
           return false;
       }
       catch (Exception e)
       {
           MessageBox.Show("Error at step 1: {0}", e.Message);
           return false;
       }
       //2. here is the new code I added today
       if (initial_fail == 1)
       {
           myComPort.BaudRate = 38400; //3. Here I changed the speed and gui text
           cmbBaudRate.Text = "38400"; //PROBLEM: when Im doing step by step debug, seems like these two lines doesnt get executed. Winform GUI remain unchanged
           try
           {
   
               portBuffer.Clear();
               myxbee.command_buffer.Clear();
               dummy = "05";
               dummy_byte = Encoding.ASCII.GetBytes(dummy);
               myxbee.command_buffer.AddRange(myxbee.myxbee_cmd.data_rate); 
               myxbee.command_buffer.AddRange(dummy_byte);
               myxbee.command_buffer.Add(myxbee.myxbee_cmd.line_feed);
               myComPort.Write(myxbee.command_buffer.ToArray(), 0, myxbee.command_buffer.ToArray().Length);
               IAsyncResult res1 = d.BeginInvoke(null, null);
               if (res1.IsCompleted == false)
               {
                   res1.AsyncWaitHandle.WaitOne(1000, false);
                   if (res1.IsCompleted == false)
                       throw new ApplicationException("Timeout"); 
                       //4. since the winform hasnt shown any bd_rate change, the program will throw a time-out here again 
               }
               if (d.EndInvoke(res1) == false)
                   throw new Exception("Fail in setting data rate to 38400");
               chkHighSpeed.Checked = true;
               high_speed_set = 1;
               MessageBox.Show("Xbee high speed");
           }
           catch (ApplicationException e)
           {
               MessageBox.Show(e.Message);
               return false;
               //5. BUT AFTER THIS TIMEOUT message, the winform's GUI will be updated to 38400, and rerun the whole test will pass
           }
   

这是 GUI 的一部分，如下所示：

所以我的问题是为什么只有在超时异常之后，波特率才会更新？

Answer 1

问题来自您在与 ui 相同的线程上创建进程的事实。SO UI 可以被您的 com 进程冻结。您可以使用更新 UI 的 doevents 方法来解决您的问题，但这不是您的最佳方法。使用后台工作人员在另一个线程上启动您的 com 进程。