private async void BTNaddCustomCourse_Click(object sender, RoutedEventArgs e)
        {
            STRBDswitch.Begin();
            await Task.Delay(100);

            FindName(nameof(FRAMEedit));
            FRAMEedit.Navigate(typeof(CourseEditPage), null);
        }
        private void LSTVWcustomCourse_ItemClick(object sender, ItemClickEventArgs e)
        {
            if (!(LSTVWcustomCourse.SelectionMode == ListViewSelectionMode.None))
            {
                return;
            }
            SimpleCustomCourseInfo t = e.ClickedItem as SimpleCustomCourseInfo;

            FindName(nameof(FRAMEedit));
            FRAMEedit.Navigate(typeof(CourseEditPage), t.Name);
        }