private void btnSignIn_Click(object sender, EventArgs e) { string tenDN = txtUsername.Text; string matkhau = txtPassword.Text; if (string.IsNullOrEmpty(tenDN) || string.IsNullOrEmpty(matkhau)) { MessageBox.Show("Please insert your username and password correctly"); } else { if (employeeBLL.CheckLogin(tenDN, matkhau) == true) { bool isAdmin = employeeBLL.CheckAdmin(tenDN); int employeeID = employeeBLL.GetEmployeeID(tenDN); Employee employ = employeeBLL.FindEmployee(employeeID); Form_Restaurant f = new Form_Restaurant(isAdmin, employeeID); this.Hide(); f.Closed += (s, args) => this.Close(); f.Show(); } else { MessageBox.Show("Incorrect. Please try again !!"); } } }