Question

Possible Duplicate:
Cross-thread operation not valid

I have a problem with using of threading in my application below are the two simple methods and this two methods are called on a button click.
I want to first run the inserting method and thread sleep for 5 seconds after 5 seconds second method run and display according to the coding.
But I face this error:

Cross-thread operation not valid: Control ‘lblDisplay’ accessed from a thread other than the thread it was created on.

Here’s the code:

private void button1_Click(object sender, EventArgs e)

    {

        Thread obj = new Thread(new ThreadStart(inserting));

        Thread obj1 = new Thread(new ThreadStart(insert));

        obj.Start();

        obj1.Start();

    }

public void inserting()
    {
        lblDisplay.Text = "inserting record......";
        Thread.Sleep(5000);
    }
    public void insert()
    {
        lblDisplay.Text = "Record successfully inserted";
    }

Answer 1

You are getting the error because you cannot access UI elements on threads other than the main UI thread (or Dispatcher thread in WPF). If you wish to have some status update system, you would be better off having the process(es) running on a separate thread, that then call back onto the main UI thread to update the status text. For example:

public void button1_Click(object sender, EventArgs e)
{
    var thread = new Thread(new ThreadStart(Execute));
    thread.Start();
}

private void Execute()
{
    UpdateStatus("Starting execution...");

    // ... Run some code ...

    UpdateStatus("Inserting record...");

    // Sleep for 5 seconds
    Thread.Sleep(5000);

    // ... Run record insertion code ...

    UpdateStatus("Record successfully inserted");
}

private void UpdateStatus(string status)
{
    // Make sure we're running on the UI thread
    if (this.InvokeRequired)
    {
        BeginInvoke(new Action<string>(UpdateStatus), status);
        return;
    }

    // Update the display text now we are running on the UI thread
    lblDisplay.Text = status;
}

Note: This is an answer specific to WinForms. For WPF, you use CheckAccess() instead of InvokeRequired and this.Dispatcher.BeginInvoke(...) instead of BeginInvoke(...).