FocusManagerExtensions

public class FocusManagerExtensions
{
    public static readonly DependencyProperty IsFocusedProperty = DependencyProperty.RegisterAttached("IsFocused", typeof(bool?), typeof(FocusManagerExtensions), new FrameworkPropertyMetadata(IsFocusedChanged));
    public static bool? GetIsFocused(DependencyObject element)
    {
        if (element == null) {
            throw new ArgumentNullException("element");
        }

        return (bool?)element.GetValue(IsFocusedProperty);
    }

    public static void SetIsFocused(DependencyObject element, bool? value)
    {
        if (element == null) {
            throw new ArgumentNullException("element");
        }

        element.SetValue(IsFocusedProperty, value);
    }

    private static void IsFocusedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        object fe = (FrameworkElement)d;

        if (e.OldValue == null) {
            fe.GotFocus += FrameworkElement_GotFocus;
            fe.LostFocus += FrameworkElement_LostFocus;
        }

        if ((bool)e.NewValue) {
            fe.Focus();
        }
    }

    private static void FrameworkElement_GotFocus(object sender, RoutedEventArgs e)
    {
        ((FrameworkElement)sender).SetValue(IsFocusedProperty, true);
    }

    private static void FrameworkElement_LostFocus(object sender, RoutedEventArgs e)
    {
        ((FrameworkElement)sender).SetValue(IsFocusedProperty, false);
    }
}