串口读取多行

Question

I have a board which I am trying to communicate with. When I give it some commands it should return string messages back and should get posted in a textbox. My problem is when the device has to return multiple lines of text only 1 of the lines gets posted. I have tried also with ReadExisting instead of ReadLine but after one command I get only empty strings back.

public partial class Form1 : Form        
{
    private string x;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        serialPort1.Open();
        timer1.Start();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        serialPort1.WriteLine(textBox1.Text);
        textBox1.Clear();
    }

    private void timer1_Tick(object sender, EventArgs e)
    {

        if (String.IsNullOrEmpty(x))
        {

        }
        else
        {
            textBox2.AppendText(x + "\n\r");
            x = "";
        }

    }

    private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
    {
        x = serialPort1.ReadLine();
        //x = serialPort1.ReadExisting();
    }

    private void Form1_Closing(object sender, EventArgs e)
    {
        serialPort1.Close();
        timer1.Stop();
    }

    private void textBox2_TextChanged(object sender, EventArgs e)
    {

    }
}

Answer 1

You're always better off avoiding DataReceived and just using BaseStream . Like this:

private async void Form1_Load(object sender, EventArgs e)
{
    serialPort1.Open();
    using (var reader = new StreamReader(serialPort1.BaseStream)) {
         while (serialPort1.IsOpen) {
             string x = await reader.ReadLineAsync();
             textBox2.AppendText(x + "\r\n");
         }
    }
}

The await keyword silently manages synchronization back to the UI thread -- you don't need Invoke , you don't get cross-thread failures, you don't get a second invocation of your event handler triggered while the first one is still running, you don't get race conditions from multiple threads accessing the same variable. Much easier to get right.

As a style issue, I wouldn't put this code directly in your Form Load event handler, I would put it in a suitably named helper function ( OpenAndReadSerial() perhaps) and call that from overridden OnLoad() .