WPF: Updating UI Elements Using Dispatcher and BackgroundWorker

If you run a BackgroundWorker object and try updating a UI element in the DoWork method, you'd get this error message:

{"The calling thread cannot access this object because a different thread owns it."}

The reason is that DoWork() method runs in a new thread and the UI elements are owned by the main thread.

A workaround is to use the Dispatcher object as shown in the following example in WPF. When Start button is clicked, a background worker runs and updates the label message:

public partial class Window1 : Window
 {
     BackgroundWorker aWorker = new BackgroundWorker();

     public Window1()
     {
         InitializeComponent();
         aWorker.WorkerSupportsCancellation = true;
         aWorker.DoWork += aWorker_DoWork;
         aWorker.RunWorkerCompleted += aWorker_RunWorkerCompleted;
     }

     private delegate void UpdateDelegate(int i);

     /// <summary>
     /// Handles the DoWork event of the aWorker control.
     /// This runs in a new thread
     /// </summary>
     /// <param name="sender">The source of the event.</param>
     /// <param name="e">The <see cref="System.ComponentModel.DoWorkEventArgs"/> instance containing the event data.</param>
     private void aWorker_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
     {
         for (int i = 0; i <= 500; i++)
         {
             Thread.Sleep(100);

             if (aWorker.CancellationPending)
             {
                 e.Cancel = true;
                 return;
             }
             UpdateDelegate update = new UpdateDelegate(UpdateLabel);
             Label1.Dispatcher.BeginInvoke(DispatcherPriority.Normal, update, i);             
         }
     }

     private void aWorker_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
     {
         if (!(e.Cancelled))
             Label2.Content = "Run Completed!";
         else
             Label2.Content = "Run Cancelled!";
     }

     private void UpdateLabel(int i)
     {
         Label1.Content = "Cycles: " + i.ToString();
     }

     private void btnStart_Click(object sender, RoutedEventArgs e)
     {
         aWorker.RunWorkerAsync();
     }

     private void btnCancel_Click(object sender, RoutedEventArgs e)
     {
         aWorker.CancelAsync();
     }
 }