Question

Whenever i am updating UI in windows form using delegate it gives me cross thread exception
why it is happening like this?
is there new thread started for each delegate call ?

void Port_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
       //this call delegate to display data
       clsConnect(statusMsg);
}




 protected void displayResponse(string resp)
 {
     //here cross thread exception occur if directly set to lblMsgResp.Text="Test";
     if (lblMsgResp.InvokeRequired)
     {
        lblMsgResp.Invoke(new MethodInvoker(delegate { lblMsgResp.Text = resp; }));
     }
 }

Answer 1

Port_DataReceived is obviously an async event handler that is being raised by a thread on port monitoring component.

is there new thread started for each
delegate call ?

No, probably not. Your port monitoring component is running the poll on a background thread and the event is being raised from that thread, every time.

The point is that it is being called on a thread other than the UI, so you will need to use Control.Invoke and the patterns associated with it.

Consider this, (and read the post that may illuminate things for you)

void Port_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
   //this call delegate to display data
   UpdateTheUI(statusMsg);
}

private void UpdateTheUI(string statusMsg)
{
    if (lblMsgResp.InvokeRequired)
    {
        lblMsgResp.BeginInvoke(new MethodInvoker(UpdateTheUI,statusMsg));
    }
    else
    {
       clsConnect(statusMsg);
    }
}

With all of that said, I would be remiss if I didn’t point out that the indirection is troubling.