Question

我正在开发一个winform程序，主要涉及Xbee和PC之间的COM端口通信。请允许我先告诉你问题：

注意：

不要担心委托函数，它只是检查返回的字节
该程序之前有效，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，然后更改为无论我需要什么，这是38400.然而，一旦我把它设置为38400，没有电源循环xbee。当我下次连接设备时，速度保持在@ 38400。这就是我添加的原因 if（initial_fail）阻止尝试连接另一个baud_rate。

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： enter image description here

所以我的问题是为什么只有在超时异常之后，才会更新波特率？

Answer 1

问题来自于你在与ui相同的线程上进行处理的事实。您的com进程可以冻结SO UI。您可以使用更新UI来解决问题的doevents方法，但这不是您的最佳方法。使用后台工作程序在另一个线程上启动您的com进程。

为什么只在抛出异常后才更新表单

1 个答案: