Handling navigation (not really an issue)

[gervaisb]

Hi there,

Thanks a lot for your project, he give a clean MVP implementation for Android. However I miss an important part; the navigation.
Imagine that you allow users to add Character. You add a button to the list with a callback method to the presenter : onAddCharacterButtonClicked and then ?

• A naive implementation can be to invoke a method on the view : setAddFormVisible(true) but then the view has to decide how you would present the form (display a view, open a dialog, move to another activity, ..). I dislike this solution.
• The other solution is then to manage that from the presenter. He can decide to add a Fragment to the view, or open it as a dialog, or start another activity. But then you cannot test your presenter because he has direct dependencies to the Context or FragmentManager.
• Some use an EventBus to send a message who is received by the Application or current Activity. But, again, I dislike the idea to use "system events" to handle navigation.
• My current solution is to write a Navigator who decide what to do (dialog, activity, ..) and has everything to do it :

public interface Navigator {
  void moveTo(Class<?> target);
}

public class AndroidNavigator implements Navigator {
  private Activity activity = null;
  public void moveTo(Class<?> target) {
    if ( SomePresenter.class.equals(target) ) {
      new DialogFragmentWhoImplementSomePresenterView().show(activity.getFragementManager(), "..");
    } else if ( AnotherPresenter.class.equals(target) ) {
      activity.startActivity(new Intent(this, ActivityWhoImplementAnotherPresenterView.class));
    }
  }

  void setCurrentActivity(Activity activity) {
    this.activity = activity;
  }
}

public abstract class BaseActivity extends ActionBarActivity {
  @Inject Navigator navigator;
  public void onCreate(Bundle savedInstanceState) {
    // ...
    (AndroidNavigator) navigator).setCurrentActivity(this);
  }
}

So that I can test everything inside plain Junit tests. This is also the solution used in EffectiveAndroidUI

Do you have a better approach ? Did you plan to describe it in your project ?