private void StudentsDataGrid_MouseDoubleClick(object sender, MouseButtonEventArgs e)
        {
            Student     student = (Student)StudentsDataGrid.SelectedItem;
            DetailedBox win     = new DetailedBox("Modify", student, this);

            win.Show();
        }
        private void AddButton_Click(object sender, RoutedEventArgs e)
        {
            DetailedBox win = new DetailedBox("Add", null, this);

            win.Show();
        }