public partial class Window1 : Window
    {
        string path;

        public Window1()
        {
           
            InitializeComponent();
           
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Window2 window = new Window2();
            window.ShowDialog();
        }
    }

 public partial class Window2 : Window
    {
        public Window2()
        {
            InitializeComponent();
            Owner = App.Current.MainWindow;
        }
    }