Access/Invalidate a label of other class in current class

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C#

WinForms

threads

Hello,

I have a dialog (WaitingDialog) that is mainly used to display the happening activities. It has a Title & Message that sets the respective labels.

public string Title {
    get { return title; }
    set { title = value;
    label1.Text = title;
    }
}
public string Message {
    get { return message; }
    set { message = value;
    msgLbl.Text = value;
    }
}
public void set(string title, string message){
    Title = title;
    Message = message;
}

In my class, I create an instance of WaitingDialog and on processing want to update its labels. I use backgroundWorker in my class. And in the methods if I try to set the Message I get InvalidException - "Cross-thread operation not valid: Control 'msgLbl' accessed from a thread other than the thread it was created on." exception. If I try to set in backgroundWorker1_RunWorkerCompleted(), it doesn't throw any exception but doesn't update the labels.

Here is the code :

// Starting backgroundWorker
backgroundWorker1.RunWorkerAsync();
// Creating WaitingDialog instance
waitDlg = new WaitingDialog("Connecting to Server ...", "");
waitDlg.ShowDialog();

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    ProcessActivity();
}

private void ProcessActivity() {
   ....
   // CONNECT TO Server
   if (ConnectToRandomServer() == false)
       activitySuceed =  false;
   return;   
}

private bool ConnectToRandomServer()
{
   .....
   if (success == false)
   {
    MessageBox.Show("Unable to connect to any Server. Please try again.");
    // HERE IT THROWS EXCEPTION 
    //waitDlg.Message = "Unable to connect to any Server. Please try again.";
    return false;
   }
   statusLabel.Text = "Retrieving Data of Server : " + selected.ServerHost;
   waitDlg.Message = "Retrieving Data of Server : " + selected.ServerHost;
    ......
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    if (activitySuceed == false)
    {
        statusLabel.Text = "Failed";
        backgroundWorker1.CancelAsync();
        waitDlg.Close();
        return;
    }
    else
    {
       // THIS WORKS PROPER - B'COZ THREAD IS COMPLETED !!
        waitDlg.set("Saving Data", "");
        IOUtility.SaveEncyptedLogin(loginDet);
        waitDlg.set("Opening...", "Ultimate VPN Client");
        OpenClient();
        waitDlg.Close();
    }
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
}

How can I achieve to set the values in the waitingDialog. Why it doesn't update the label text's?

Any help is highly appreciated.

Thanks