Can't set focus to a child of UserControl

Question

I have a UserControl which contains a TextBox. When my main window loads I want to set the focus to this textbox so I added Focusable=\"True

Answer 1

I converted fuzquat's answer to an extension method. I'm using this instead of Focus() where Focus() did not work.

using System;
using System.Threading;
using System.Windows;

namespace YourProject.Extensions
{
    public static class UIElementExtension
    {
        public static void WaitAndFocus(this UIElement element, int ms = 100)
        {
            ThreadPool.QueueUserWorkItem(f =>
            {
                Thread.Sleep(ms);

                element.Dispatcher.Invoke(new Action(() =>
                {
                    element.Focus();
                }));
            });
        }
    }
}