create Wpf user controls in other thread

Question

I am trying to create some UserControl(s) using another thread, and I am using code like this:

    private void btnDemo_Click(object sender, RoutedEventArgs e)
    {
      Task tsk = Task.Factory.StartNew(() =>
      {
        for (int i = 0; i < 3; i++)
        {
          MyControl sprite = new MyControl();
          pnlTest.Children.Add(sprite);
        }
      });
    }

But I am getting this exception in the UserControl constructor:

The calling thread must be STA, because many UI components require this.

I am not sure that I am using the right approach to do this. Please, Can you help me with this.

thanks.

Answer 1

The creating of the controls can be done on any Thread but Adding them to the GUI needs to be synchronized to the main Thread.

In this case, just 3 controls, forget about Tasks and just do it directly, single-threaded.

Answer 2

You can dispatch the operation of adding controls to the Children collection to the UI thread using Dispatcher:

private void btnDemo_Click(object sender, RoutedEventArgs e)
{
  Task tsk = Task.Factory.StartNew(() =>
  {
    for (int i = 0; i < 3; i++)
    {
      Dispatcher.BeginInvoke(new Action(() => {
         MyControl sprite = new MyControl();
         pnlTest.Children.Add(sprite);
      }));
    }
  });
}

By calling BeginInvoke on Dispatcher you basically adding the operation to the queue to execute on the UI thread.