C# winform解析串口数据

Question

I am a newb armed with copy paste trying to get data from an old Avery-Weightronix 7820 weigh scale. I have it hooked up via an RJ-232 cable and have managed to get responses from the scale. I followed this tutorial https://www.studentcompanion.co.za/creating-a-serial-port-interface-with-c/ to get up and running.

Once I got it working I wanted to simplify it and essentially use my computer as a remote display. I hard coded the serial connection parameters and set up the code to send a request for the weight every second so I could display it in a winform.

Later I plan to extend it so I can get the total weight for multiple items. I plan to weigh an item, copy the weight to a running total, put a new item on the scale and repeat.

I am stuck at the moment because I am having trouble consistently parsing the data returned from the scale and because the loop locks up the UI.

When I send W <CR> which is the request for the current weight, an example response is:

<LF> 0001.10lb <CR> <LF> 00 <CR><ETX>

Where <ETX> = End of text character (Ø3 hex), <LF> = Line feed character (ØA hex), <CR> = Carriage return character (ØD hex).

The response from the scale is fixed length but when I go into debug mode the response is not received during the first couple of cycles through the code. Then it arrives later. This is ok when I am outputting it to a rich text field but when I try to pull out a substring I get an error if there is no data.

Also, the UI locks and the only thing I can do it stop the execution. From reading around it seems I should implement threading but I am unsure how to reorganize my code to do this.

I would appreciate any pointers or advice on how to solve these issues.

This is the code I have:

using System;
using System.Drawing;
using System.Windows.Forms;
using System.IO.Ports;

namespace ScaleView
{
  public partial class Form1 : Form
  {
    public Form1()
    {
        InitializeComponent();
    }

    private void groupBox1_Enter(object sender, EventArgs e)
    {

    }


    private void Form1_Load(object sender, EventArgs e)
    {
        //updatePorts();           //Call this function everytime the page load 
                                 //to update port names
        CheckForIllegalCrossThreadCalls = false;
    }
    

    private SerialPort ComPort = new SerialPort();  //Initialise ComPort Variable as SerialPort
    private void connect()
    {
        bool error = false;

            
        ComPort.PortName = "COM3";
        ComPort.BaudRate = int.Parse("9600");      //convert Text to Integer
        ComPort.Parity = (Parity)Enum.Parse(typeof(Parity), "Even"); //convert Text to Parity
            ComPort.DataBits = int.Parse("7");        //convert Text to Integer
            ComPort.StopBits = (StopBits)Enum.Parse(typeof(StopBits), "1");  //convert Text to stop bits

            try  //always try to use this try and catch method to open your port. 
                 //if there is an error your program will not display a message instead of freezing.
            {
                //Open Port
                ComPort.Open();
                ComPort.DataReceived += SerialPortDataReceived;  //Check for received data. When there is data in the receive buffer,
                                                                 //it will raise this event, we need to subscribe to it to know when there is data
                                                                 //MessageBox.Show(this, "Connected", MessageBoxButtons.OK);
            }
            catch (UnauthorizedAccessException) { error = true; }
            catch (System.IO.IOException) { error = true; }
            catch (ArgumentException) { error = true; }

            if (error) MessageBox.Show(this, "Could not open the COM port. Most likely it is already in use, has been removed, or is unavailable.", "COM Port unavailable", MessageBoxButtons.OK, MessageBoxIcon.Stop);

        
       
        //if the port is open, Change the Connect button to disconnect, enable the send button.
        //and disable the groupBox to prevent changing configuration of an open port.
        if (ComPort.IsOpen)
        {
            btnConnect.Text = "Disconnect";
        }
    }
    // Call this function to close the port.
    private void disconnect()
    {
        ComPort.Close();
        btnConnect.Text = "Connect";
        
    }
    //whenever the connect button is clicked, it will check if the port is already open, call the disconnect function.
    // if the port is closed, call the connect function.
    private void btnConnect_Click_1(object sender, EventArgs e)

    {
        if (ComPort.IsOpen)
        {
            disconnect();
        }
        else
        {
            connect();
            rtxtDataArea.AppendText("Connected\n");
            sendData();
        }
    }

    private void btnClear_Click(object sender, EventArgs e)
    {
        //Clear the screen
        rtxtDataArea.Clear();
    }
    // Function to send data to the serial port
    private void sendData()
    {
        bool error = false;
        while(ComPort.IsOpen)        //if text mode is selected, send data as tex
        {
            
            try
            {
                // Convert string of hex digits (in this case representing W<CR>) to a byte array
                string hextext = "57 0D";
                byte[] data = HexStringToByteArray(hextext);

                // Send the binary data out the port
                ComPort.Write(data, 0, data.Length);
                System.Threading.Thread.Sleep(3000);

                rtxtDataArea.ForeColor = Color.Blue;   //write Hex data in Blue
                string response = ComPort.ReadLine();
                int charfrom = 1;
                int charto = 9;
                //string weight = response.Substring(charfrom, charto - charfrom);
                rtxtDataArea.AppendText(response + "TEST\n");
                
            }
            catch (FormatException) { error = true; }

            // Inform the user if the hex string was not properly formatted
            catch (ArgumentException) { error = true; }

            if (error) MessageBox.Show(this, "Not properly formatted hex string: \n" + "example: E1 FF 1B", "Format Error", MessageBoxButtons.OK, MessageBoxIcon.Stop);

        }
    }
    //Convert a string of hex digits (example: E1 FF 1B) to a byte array. 
    //The string containing the hex digits (with or without spaces)
    //Returns an array of bytes. </returns>
    private byte[] HexStringToByteArray(string s)
    {
        s = s.Replace(" ", "");
        byte[] buffer = new byte[s.Length / 2];
        for (int i = 0; i < s.Length; i += 2)
            buffer[i / 2] = (byte)Convert.ToByte(s.Substring(i, 2), 16);
        return buffer;
    }

    private void btnSend_Click(object sender, EventArgs e)
    {
        sendData();
    }
    //This event will be raised when the form is closing.
    private void Form1_FormClosing(object sender, FormClosingEventArgs e)
    {
        if (ComPort.IsOpen) ComPort.Close();  //close the port if open when exiting the application.
    }
    //Data recived from the serial port is coming from another thread context than the UI thread.
    //Instead of reading the content directly in the SerialPortDataReceived, we need to use a delegate.
    delegate void SetTextCallback(string text);
    private void SetText(string text)
    {
        //invokeRequired required compares the thread ID of the calling thread to the thread of the creating thread.
        // if these threads are different, it returns true
        if (this.rtxtDataArea.InvokeRequired)
        {
            rtxtDataArea.ForeColor = Color.Green;    //write text data in Green colour

            SetTextCallback d = new SetTextCallback(SetText);
            this.Invoke(d, new object[] { text });
        }
        else
        {
            this.rtxtDataArea.AppendText(text);
        }
    }
    private void SerialPortDataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        var serialPort = (SerialPort)sender;
        var data = serialPort.ReadExisting();
        SetText(data);
    }

    private void rtxtDataArea_TextChanged(object sender, EventArgs e)
    {

    }
}
}

Answer 1

Remove try-catch blocks, and MessageBox.Show(...) in both the connect() and sendData() methods. The try-catch in the new Thread(() => { block will catch any exceptions and send them to the UI thread.

Delete the line CheckForIllegalCrossThreadCalls = false; because it bypasses the built-in protection. The serialPort.ReadLine(); method might be better than serialPort.ReadExisting(); as ReadLine() will wait for a full line of data.

This should give you an idea of how the code might look:

Thread dataThread = null;
private void btnConnect_Click_1(object sender, EventArgs e) {
    if (ComPort.IsOpen) {
        disconnect();
    }
    else {
        btnConnect.Enabled = false; // user has to wait for connection to succeed or fail. Prevents clicking the button twice.
        Form form = this;

        dataThread = new Thread(() => {
            try {
                connect();

                // if you get here then connect succeeded
                form.BeginInvoke((Action) delegate {
                    btnConnect.Enabled = true; // now becomes the Disconnect button
                    rtxtDataArea.AppendText("Connected\n");
                });

                // start sending and receiving data on the thread
                sendData();
            } catch (Exception ex) {
                form.BeginInvoke((Action) delegate {
                    btnConnect.Enabled = true; // remains as the Connect button, user can try again
                    MessageBox.Show(form, ex.GetType().Name + ": " + ex.Message, "COM Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                });
            }
        });
        dataThread.IsBackground = true;
        dataThread.Start();
    }
}

delegate void SetTextCallback(string text);
private SetTextCallback callSetText = new SetTextCallback(SetText); // don't create new delegates each time
    private void SetText(string text) {
    if (this.rtxtDataArea.InvokeRequired) {
        rtxtDataArea.ForeColor = Color.Green;    //write text data in Green colour
        this.BeginInvoke(d, new object[] { text }); // use BeginInvoke instead
    }
    else {
        this.rtxtDataArea.AppendText(text);
    }
}