Update label from another thread [duplicate]

Question

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

Answer 1

You cannot update UI from any other thread other than the UI thread. Use this to update thread on the UI thread.

 private void AggiornaContatore()  {               if(this.lblCounter.InvokeRequired)      {          this.lblCounter.BeginInvoke((MethodInvoker) delegate() {this.lblCounter.Text = this.index.ToString(); ;});          }      else      {          this.lblCounter.Text = this.index.ToString(); ;      }  } 

Please go through this chapter and more from this book to get a clear picture about threading:

http://www.albahari.com/threading/part2.aspx#_Rich_Client_Applications