private void btnAdd_Click(object sender, EventArgs e) { if (CheckData() == true) { if (Check_CustomerIDtExist() == true) { DTO_Customer dto_cus = new DTO_Customer(txtCustomerID.Text, txtName.Text, Birthday.Value.ToShortDateString(), txtGender.Text, txtAddress.Text, txtEmail.Text, txtPhonenumber.Text); if (bus_cus.Add(dto_cus)) { MessageBox.Show("ADDING SUCCESS!", "ADD", MessageBoxButtons.OK, MessageBoxIcon.Information); LoadData(); ResetValues(); } else { MessageBox.Show("ADDING FAIL!", "ADD", MessageBoxButtons.OK, MessageBoxIcon.Error); } } else { MessageBox.Show("' " + txtCustomerID.Text + "' already exists!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error); } } }