Extending RoleAssignmentScreen

Hi,

When i assigned role to user from user screen, i am able to add multiple roles to the user.
I want only single role to be assigned to the user. So i tried extending RoleAssignmentScreen to modify but methods are not getting overriden.

@Primary
@UiController("sec_RoleAssignmentScreen")
@UiDescriptor("role-assignment-screen.xml")
public class CustomRoleAssignmentScreen extends RoleAssignmentScreen {

@Override
protected void initScreenActions(){
}

}

resorcepermission
roleAsign

Kindly suggest any possible solution to restrict user for selecting more than one role.