Question

I need to implement an auto logout feature in C#. Previously i have asked a similiar question before and i managed to implement it using the System.Windows.Forms.Timer . But right now i have a additional requirement apart from resetting the timer when the user move the mouse or enters a key i also need to reset the timer when a new message is received via the serial port ( DataReceived event handler ).

serialPort.DataReceived += port_DataRecieved;

I need to include the reset function in a portion of the port_DataRecieved function. I cannot simply add another delegate method to the serialPort.DataReceived which will perform the reset as the serialPort.DataReceived will received a lot of other messages that i am not interested in. I want to perform a reset when the message that i am interested in arrives. And i know where to put the reset feature. The issue is that the timer does not reset in port_DataRecieved method. And i cannot achieve the desired result using the System.Threading.Timer. Anyone can guide me or provide some suggestion on this issue ? Any help provided will be greatly apperciated.

public partial class Form1: Form
{  

    private System.Windows.Forms.Timer sessionTimer = new System.Windows.Forms.Timer();

    public Form1()
    {
        initialiseTimer(); 
    } 

    private void port_DataRecieved(object sender, SerialDataReceivedEventArgs e)
    {
        try
        {
            serialPort= (SerialPort)sender;
            str = serialPort.ReadExisting();
            string[] split = str.Split(Convert.ToChar(10));
            for (int i = 1; i < split.Length; i++)
            {
                str = split[i];
                if (split[i].StartsWith("+CMTI:"))
                {
                    sessionTimer.Stop();
                    sessionTimer.Start();

                    //Other codes
                }
            }
        }
        catch (Exception)
        {
            MessageBox.Show("Error processing received commands !", "CONNECTION ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
            sendRecPort.Close();
        }
    }

    private void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        sessionTimer.Stop();
        sessionTimer.Start(); 
    }

    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        sessionTimer.Stop();
        sessionTimer.Start(); 
    }

    private void initialiseTimer()
    {
        sessionTimer.Interval = (5 * 60 * 1000);        
        sessionTimer.Tick += new EventHandler(logOutUser);
        sessionTimer.Stop();
        sessionTimer.Start();
    }

    private void logOutUser(object sender, EventArgs e)
    {
        // logout the user
        this.Hide();
        //Open up the login Form
        login.Show();
    }

}

Answer 1

Your problem is that the the DataReceived event is being executed on a thread other than the UI thread. You’re trying to modify the timer (a UI object) from a non-UI thread. This typically throws an exception, but it’s possible that the method that issues the DataReceived event is swallowing that exception.

From the documentation for the DataReceived event:

The DataReceived event is raised on a
secondary thread when data is received
from the SerialPort object. Because
this event is raised on a secondary
thread, and not the main thread,
attempting to modify some elements in
the main thread, such as UI elements,
could raise a threading exception. If
it is necessary to modify elements in
the main Form or Control, post change
requests back using Invoke, which will
do the work on the proper thread.

You need to synchronize with the UI thread to set the timer.

void ResetTimer()
{
    sessionTimer.Stop();
    sessionTimer.Start();
}

private void port_DataRecieved(object sender, SerialDataReceivedEventArgs e)
{
    //Other codes
    this.Invoke((MethodInvoker)delegate { ResetTimer(); });
    //Other codes
}