[c#] Update label from another thread

I use a thread writing in another class for update a label. The label is contents in Winform Main class.

 Scanner scanner = new Scanner(ref lblCont);
 scanner.ListaFile = this.listFiles;
 Thread trd = new Thread(new ThreadStart(scanner.automaticScanner));
 trd.IsBackground = true;
 trd.Start();
 while (!trd.IsAlive) ;
 trd.Join();

How you can see, i pass the reference of label into constructor of the second class. In the second class(Scanner) i've a method called "automaticScanner" that should update the label with this code:

public Scanner(ref ToolStripStatusLabel _lblContatore)
{
        lblCounter= _lblContatore;
}
Thread threadUpdateCounter = new Thread(new ThreadStart(this.UpdateCounter));
threadUpdateCounter.IsBackground = true;
threadUpdateCounter.Start();
while (!threadUpdateCounter .IsAlive) ;
threadUpdateCounter.Join();

private void AggiornaContatore()
{
  this.lblCounter.Text = this.index.ToString();        
}

I've receive this error on update of label:

Cross-thread operation not valid: Control 'Main' accessed from a thread other than the thread it was created on

I use .net 4 with Winform C#.

Thanks a lot for answers.

News: The problem is this line:

trd.Join();

This line block my GUI and the lable was not update. There are methods to control the finish of thread and updating the label until the end? Thanks

Just use Control.Invoke Method or Control.BeginInvoke Method.

Great example: How to: Make Thread-Safe Calls to Windows Forms Controls.

Use MethodInvoker for updating label text in other thread.

private void AggiornaContatore()
{
    MethodInvoker inv = delegate 
    {
      this.lblCounter.Text = this.index.ToString(); 
    }

 this.Invoke(inv);
}

You are getting the error because your UI thread is holding the label, and since you are trying to update it through another thread you are getting cross thread exception.

You may also see: Threading in Windows Forms