WPF Focus Extension

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

namespace UI.Extensions
{
    /// <summary>
    /// Extension to focus UI controls via ViewModels.
    /// xaml: <TextBox Text="Set Text Before FocusExtension to SelectAll" ext:FocusExtension.IsFocused="True" />
    /// Remember to add 'xmlns:ext="clr-namespace:UI.Extensions"' to xaml namespaces
    /// </summary>
    public static class FocusExtension
    {
        public static bool? GetIsFocused(DependencyObject obj)
        {
            return (bool?)obj.GetValue(IsFocusedProperty);
        }

        public static void SetIsFocused(DependencyObject obj, bool? value)
        {
            obj.SetValue(IsFocusedProperty, value);
        }

        public static readonly DependencyProperty IsFocusedProperty =
                DependencyProperty.RegisterAttached(
                 "IsFocused", typeof(bool?), typeof(FocusExtension),
                 new UIPropertyMetadata(false, OnIsFocusedPropertyChanged));

        private static void OnIsFocusedPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var uie = d as UIElement;
            if (uie == null)
                return;

            if (e.NewValue == null)
                return;

            if ((bool)e.NewValue)
            {
                uie.Focus(); // Don't care about false values.
                TextBox tb = uie as TextBox;
                if (tb != null)
                {
                    if (!string.IsNullOrEmpty(tb.Text))
                        tb.SelectAll();
                }
            }
        }
    }
}