public static PInvokeDemo Show()
        {
            var window = instance as Window;
            if (window == null)
                window = instance = new PInvokeDemo();

            window.Show();
            window.Focus();
            return instance;
        }
        public static PInvokeDemo Show()
        {
            var window = instance as Window;

            if (window == null)
            {
                window = instance = new PInvokeDemo();
            }

            window.Show();
            window.Focus();
            return(instance);
        }
 private void Button_Click_1(object sender, RoutedEventArgs e)
 {
     PInvokeDemo.Show();
 }