title: Call implemented interfaces from service?
body: <p>Not sure if this is possible, but I would like the service to call implemented methods like below.</p>
  
  <p>Prism has an <code>INavigatingAware</code> that viewmodels can implement. I want to follow the same pattern and add my own interface like below.</p>
  
  <p>Using Prism and Xamarin.</p>
  
  <pre><code>public interface ILoginAware
  {
      void LoggedIn(Customer customer);
      void LoggedOut();
  }
  
  public class ProfilePageViewModel : ILoginAware
  {
      public void LoggedIn(Customer customer) =&gt; ShowAuthenticatedViews(customer);
      public void LoggedOut() =&gt; ShowNotAuthenticatedViews();
  }
  
  public class CustomerService
  {
      public void Login()
      {
          var customer = DoLogin();
          // How to call ProfilePageViewModel.LoggedIn(customer) from here?
      }
  }
  </code></pre>