Selecting text on keyboard navigation in WPF

App.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);
        RegisterClassHandlers();
        Window window/* = ... */;
        window.Show();
    }

    private void RegisterClassHandlers()
    {
        EventManager.RegisterClassHandler(
            typeof(TextBox),
            UIElement.GotKeyboardFocusEvent,
            new KeyboardFocusChangedEventHandler(TextBox_GotKeyboardFocus));
        EventManager.RegisterClassHandler(
            typeof(TextBox),
            UIElement.LostFocusEvent,
            new RoutedEventHandler(TextBox_LostFocus));
    }

    private void TextBox_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
    {
        if (e.KeyboardDevice.IsKeyDown(Key.Tab))
        {
            ((TextBox)sender).SelectAll();
        }
    }

    private void TextBox_LostFocus(object sender, RoutedEventArgs e)
    {
        ((TextBox)sender).Select(0, 0);
    }
}