private void set_black_out_dates(DateTime start, DateTime end) { Test_datePicker.BlackoutDates.Clear(); trainee.Address = AddressTextBox.Text.ToAddress(); DateTime i = start.Date; while(i <= end) { var v = myBL.Available_testers_by_day_nearby(i, trainee.Address, trainee.Car_type, trainee.Gear_type); if (v.Count() == 0) Test_datePicker.BlackoutDates.Add(new CalendarDateRange(i)); i = i.AddDays(1); } }