private void Addbt_Click(object sender, RoutedEventArgs e)
        {
            AddGroup a = new AddGroup();

            fr.Navigate(a);
            //  MainWindow m = new MainWindow();
            // this.Content = a;
        }
        private void Addbt_Click(object sender, RoutedEventArgs e)
        {
            AddGroup a = new AddGroup();

            fr.Navigate(a);
        }