when receive data, [serialport_datareceived] event occur more than once(using virtual serial port)

Question

I'm trying to send data and receive through serial communication using virtual serial port program. But here is problem... Let's suppose A is transmit data and B is receive data.

When A send data to B. B receive data twice(serialport_datareceived event occur twice!).

Every time when B close serialport and open again, serialport_datareceived event occur increase.

I can't figure out why is this happening.

A(transmit)
BaudRate = 9600
Parity = None
DataBits = 8
StopBits = 1

    public transmit()
    {
        InitializeComponent();
        foreach (String s in System.IO.Ports.SerialPort.GetPortNames())
        {
            cBoxPort.Items.Add(s);          
        }
    }
    private void CBoxBaudRate_SelectedIndexChanged(object sender, EventArgs e)
    {
        serialPort1.BaudRate = Convert.ToInt32(cBoxBaudRate.Text);                          
    }
    private void CBoxStopBits_SelectedIndexChanged(object sender, EventArgs e)
    {
        serialPort1.StopBits = (StopBits)Enum.Parse(typeof(StopBits), cBoxStopBit.Text);   
    }
    private void CBoxDataBits_SelectedIndexChanged(object sender, EventArgs e)
    {
        serialPort1.DataBits = Convert.ToInt32(cBoxDataBits.Text);                          
    }
    private void CBoxParityBits_SelectedIndexChanged(object sender, EventArgs e)
    {
        serialPort1.Parity = (Parity)Enum.Parse(typeof(Parity), cBoxParity.Text);           
    }

    private void btnConnect_Click(object sender, EventArgs e)
    {
        try
        {
            serialPort1.PortName = cBoxPort.Text;
            serialPort1.BaudRate = Convert.ToInt32(cBoxBaudRate.Text);
            serialPort1.DataBits = Convert.ToInt32(cBoxDataBits.Text);
            serialPort1.StopBits = (StopBits)Enum.Parse(typeof(StopBits), cBoxStopBit.Text);
            serialPort1.Parity = (Parity)Enum.Parse(typeof(Parity), cBoxParity.Text);
            serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);
            serialPort1.Open();

            txtReceive.AppendText("Connected\n");   
            btnConnect.Enabled = false;             
            btnClose.Enabled = true;
            btnSend.Enabled = true;
        }

        catch (Exception ex)
        {
            return;
        }
    }
    private void btnClose_Click(object sender, EventArgs e)
    {
        if (serialPort1.IsOpen)
        {
            serialPort1.Close();                        
            btnClose.Enabled = false;
            btnConnect.Enabled = true;
            btnSend.Enabled = false;
            txtReceive.AppendText("Disconnected\n");  
        }
    }

    private void btnSend_Click(object sender, EventArgs e)
    {
        byte[] bytesend = { 0x00 };
        Debug.WriteLine("111");
        serialPort1.Write(bytesend, 0, bytesend.Length);
    }

    private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        Debug.WriteLine("444");
    }

}

B(receive)

    byte[] bytesend;

    //Initial Conditions(SerialPort)
    private void receive_Load(object sender, EventArgs e)
    {
        cBoxBaudRate.SelectedIndex = 0;     //BaudRate = 9600
        cBoxParity.SelectedIndex = 0;       //Parity = None
        cBoxDataBits.SelectedIndex = 0;     //DataBits = 8
        cBoxStopBit.SelectedIndex = 0;      //StopBits = 1
        cBoxPort.SelectedIndex = 1;         

        btnConnect.Enabled = true;
        btnClose.Enabled = false;
    }

    //Show usable CommPort
    public receive()
    {
        InitializeComponent();
        foreach (String s in System.IO.Ports.SerialPort.GetPortNames())
        {
            cBoxPort.Items.Add(s);
        }
    }

    //Connection
    private void btnConnect_Click(object sender, EventArgs e)
    {
        serialPort1.PortName = cBoxPort.Text;
        serialPort1.BaudRate = Convert.ToInt32(cBoxBaudRate.Text);
        serialPort1.DataBits = Convert.ToInt32(cBoxDataBits.Text);
        serialPort1.StopBits = (StopBits)Enum.Parse(typeof(StopBits), cBoxStopBit.Text);
        serialPort1.Parity = (Parity)Enum.Parse(typeof(Parity), cBoxParity.Text);
        serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);
        serialPort1.Open();

        btnConnect.Enabled = false;
        btnClose.Enabled = true;
    }
    private void btnClose_Click(object sender, EventArgs e)
    {
        if (serialPort1.IsOpen)
        {
            serialPort1.Close();
            btnClose.Enabled = false;
            btnConnect.Enabled = true;
        }
    }

    private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        Debug.WriteLine("222");
    }

when i debug this code output represent 111 222 222. And when i press the close and connect button, the output represent 111 222 222 222.

Answer 1

Every time when B close serialport and open again, serialport_datareceived event occur increase.

Right, because like I said, you should only be wiring up the DataReceived event ONCE. Each time you click the button another handler gets added, resulting in the multiple firing for a single receive. This has nothing to do with multi-threading. Move the line that wires up the handler from the button click event up to the Load event:

private void transmit_Load(object sender, EventArgs e)
{
    serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived); // now it only gets called once
    // ... other existing code ...
}


private void btnConnect_Click(object sender, EventArgs e)
{
    try
    {
        serialPort1.PortName = cBoxPort.Text;
        serialPort1.BaudRate = Convert.ToInt32(cBoxBaudRate.Text);
        serialPort1.DataBits = Convert.ToInt32(cBoxDataBits.Text);
        serialPort1.StopBits = (StopBits)Enum.Parse(typeof(StopBits), cBoxStopBit.Text);
        serialPort1.Parity = (Parity)Enum.Parse(typeof(Parity), cBoxParity.Text);
        // serialPort1.DataReceived += new SerialDataReceivedEventHandler(serialPort1_DataReceived);  // remove this line
        serialPort1.Open();

        txtReceive.AppendText("Connected\n");   
        btnConnect.Enabled = false;             
        btnClose.Enabled = true;
        btnSend.Enabled = true;
    }

    catch (Exception ex)
    {
        return;
    }
}

You need to do the same thing in your receive form as well.