private void bt_Click(object sender, EventArgs e) { if (string.IsNullOrEmpty((sender as SimpleButton).Text)) { return; } else { DateTime dt = new DateTime(dateTimePicker1.Value.Year, dateTimePicker1.Value.Month, Convert.ToInt32((sender as SimpleButton).Text)); dateTimePicker1.Value = dt; KhachHangDao kh = new KhachHangDao(); if (kh.LoadNgaySinh(dateTimePicker1.Value) != null && kh.LoadNgaySinh(dateTimePicker1.Value).Count > 0) { ThongBao tb = new ThongBao(dateTimePicker1.Value); tb.ShowDialog(); } } }