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。请允许我首先说明问题：

注：

1. 不用担心委托函数，它只是检查返回字节

2. 该项目工程之前，我只是今天增加了高速设置。所以 为xbee设备，我必须先从9600速度，然后改为 无论我需要什么，这是38400.但是，一旦我将它设置为38400, 没有权力循环xbee。当我下次连接设备 时，速度依然为@ 38400。这就是我添加 if（initial_fail）块试图与另一个baud_rate连接的原因。

3. 请跟随我打上编号

   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的部分看起来像评论：

所以我的问题是，为什么超时异常后只，那么波特率会被更新？

Answer 1

问题来自于你在与ui相同的线程上创建进程。 SO用户界面可以被你的com进程冻结。 您可以使用更新UI来解决您的问题的doevents方法，但这不是您的情况中最好的方法。 使用后台工作器在另一个线程上启动com进程。