Hide one field when another change

Hi, I'm trying to hide one field without sucess. I saw a lot of examples but I can't solve my case. I create a new module hr_payroll_sn, where I have the py file hr_payroll_sn and the xml file hr_payroll_sn_view. In the py file, I have a class whitch inherit hr.employee and I add a new integer field wife_number. I want to hide the wife_number field when the field marital change, but it doesn't work. The xml file is below: hr.payroll.sn.employee.view.formhr.employee