private void btnCustomerLogin_Click(object sender, EventArgs e) { Customer customer = LoginValidator.ValidateCustomer(tbxCustomerLoginId.Text, tbxCustomerLoginPassword.Text); ParentForm mainForm = (ParentForm)MdiParent; if (customer != null) { mainForm.CustomerLogin(customer); this.Hide(); //Login } else { MessageBox.Show("Login Failed!\nWrong Id or Password"); } }