private async void SubmitAttendance_Clicked(object sender, EventArgs e)
        {
            List <string> selected         = new List <string>();
            List <string> teachersSelected = new List <string>();

            foreach (ViewCell c in Backup)
            {
                StackLayout sl = c.View as StackLayout;
                CheckBox    cb = sl.Children[3] as CheckBox;
                Label       l  = sl.Children[0] as Label;

                if (cb.IsChecked && Backup.Contains(c))
                {
                    selected.Add(l.Text);
                }
            }

            foreach (ViewCell c in TeacherBackup)
            {
                StackLayout sl = c.View as StackLayout;
                CheckBox    cb = sl.Children[3] as CheckBox;
                Label       l  = sl.Children[0] as Label;

                if (cb.IsChecked && TeacherBackup.Contains(c))
                {
                    teachersSelected.Add(l.Text);
                }
            }

            var answer = await DisplayAlert("Submit", "Please verify there are " + selected.Count + " students and " + teachersSelected.Count + " Teachers.", "continue", "cancel");

            if (answer)
            {
                Attendance.TakeAttendance(selected, DatePicker.Date);
                Attendance.TakeTeacherAttendance(teachersSelected, DatePicker.Date);
                await Navigation.PopAsync();
            }
        }