Custom Role provider vs Custom Authorize attribute.

Question

we can set Principle while creating our Custom authorizing attribute like

public class BasicAuthenticationAttribute : AuthorizationFilterAttribute
{
   //todo
   IPrincipal principal = new GenericPrincipal(identity, UserDetails.Roles.Split(','));
}

and we can also create CustomRoleProvider like below

public class UserRoleProvider : RoleProvider
{
        public override string[] GetRolesForUser(string username)
        {
            using (EmployeeContext _Context=new EmployeeContext())
            {
                var userRoles =  //todo
                return userRoles;
            }
        }
    }
}

My question is what is the difference between the two and when to use one over another or both are same?