private void Search_CourseByCategory_Click(object sender, RoutedEventArgs e)
        {
            StudentSearchCoursViewModel regvmInstance = new StudentSearchCoursViewModel();

            this.DataContext = regvmInstance;
            regvmInstance.SelectedCategoryID = comboSearchCourse.SelectedIndex;
        }
        private void Button_Search_Course_Click(object sender, RoutedEventArgs e)
        {
            StudentSearchCoursViewModel regvmInstance = new StudentSearchCoursViewModel();

            this.DataContext = regvmInstance;
        }