private void btnAdd_Click(object sender, EventArgs e)
        {
            AddSalesman a = new AddSalesman(null);

            a.Visible    = true;
            this.Visible = false;
        }
        private void btnEdit_Click(object sender, EventArgs e)
        {
            if (salesmanDetailsBindingSource.Current == null)
            {
                return;
            }

            using (AddSalesman am = new AddSalesman(salesmanDetailsBindingSource.Current as Salesman_Details))
            {
                if (am.ShowDialog() == DialogResult.OK)
                {
                    salesmanDetailsBindingSource.DataSource = cmd.Salesman_Details.ToList();
                }
            }
        }