private void BtnDeleteEmployee(object sender, RoutedEventArgs e)
        {
            Employee emp = new Employee();

            emp.EmpID = Int32.Parse(txtEmpId.Text);

            string msg = da.DeleteEmployee(emp);

            MessageBox.Show("" + msg);
            if (msg.Equals("Employee Discontinued"))
            {
                MainWindow mw = Application.Current.Windows.OfType <MainWindow>().FirstOrDefault();
                if (mw != null)
                {
                    mw.MainFrame.Content = new ManageEmployees();
                }
            }
        }