How to fix "The calling thread cannot access this object because a different thread owns it." on a WPF app

Question

I have the following WPF code and it gives me an exception at "TextBox t = tabItem.Content as TextBox;" the error says "The calling thread cannot access this object because a different thread owns it." How can I fix the exception?

Regards!

private void btnAdd_Click(object sender, RoutedEventArgs e)
{
  RichTextBox statusRichTextBox = new RichTextBox();
  CloseableTabItem tabItem = new CloseableTabItem();
  tabItem.Content = statusRichTextBox;
  tabItem.Header = "New Tab";
  MainTab.Items.Add(tabItem);
  Thread t = new Thread(new ParameterizedThreadStart(worker));
  t.Start(tabItem); 
}


public void worker(object threadParam)
{
  CloseableTabItem tabItem = (CloseableTabItem)threadParam;

  TextBox t = tabItem.Content as TextBox; //exception here
  if (t != null)
    Window1.myWindow1.Dispatcher.BeginInvoke((Action)(() => { t.Text = "THIS IS THE TEXT"; }), System.Windows.Threading.DispatcherPriority.Normal);
}

Answer 1

Properties and methods of UI objects can only be accessed on the thread that created these objects, so when you try to access tabItem.Content on a worker thread, it fails.

You can do that instead:

TextBox t;
Window1.myWindow1.Dispatcher.Invoke(new Action(() => t = tabItem.Content as TextBox));