Update label from another thread

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

User · Answer

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

User · Answer

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

User · Answer

Just use Control Invoke Method or Control BeginInvoke Method   Great example  How to  Make Thread-Safe Calls to Windows Forms Controls

[c#] Update label from another thread

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