private void button1_Copy2_Click_1(object sender, RoutedEventArgs e)
        {
            if (courses_listView.SelectedIndex == -1)
            {
                return;
            }

            _Courses.AddNewCourse nc = new _Courses.AddNewCourse();
            nc.EditedCourse = (Course)courses_listView.SelectedItem;
            nc.ShowDialog();
        }
 private void button2_Click(object sender, RoutedEventArgs e)
 {
     _Courses.AddNewCourse nc = new _Courses.AddNewCourse();
     nc.ShowDialog();
 }