Mortar + Flow with third party libraries hooked to activity lifecycle

Question

Some third party libraries use hooks into the activity lifecycle to work correctly - for instance, the Facebook SDK (https://developers.facebook.com/docs/android/login-with-facebook/).

I'm having some trouble figuring out how to reconcile this model cleanly with a single-activity flow+mortar setup.

For instance, if I want to use Facebook login as part of a login Flow (w/ FlowView/FlowOwner), but not otherwise in the activity, what's the smartest way to pull this off if you need hooks for that particular flow in onCreate, onResume, onPause, onDestroy, onSaveInstanceState, onActivityResult, etc?

It's not immediately obvious what the cleanest path is - create an observable for each lifecycle activity stage and subscribe the flow to it? Seems like that path quickly devolves to the same Android lifecycle if you're not careful. Is there a better way?

I love the single activity model, and I'd really like to keep everything managed by flow/mortar and not activities, if possible. Or am I thinking about this in a way that is fundamentally making it more difficult than it should be?

Answer 1

We haven't had a need for start and stop so far, but do have a few spots that rely on pause and resume. We use an ActivityPresenter as you suggest, but avoid any kind of universal superclass. Instead it exposes a service that interested presenters can opt in to. This kind of hookup need is why the onEnterScope(Scope) method was added. Here's the code.

First, have the activity implement this interface:

/**
 * Implemented by {@link android.app.Activity} instances whose pause / resume state
 * is to be shared. The activity must call {@link PauseAndResumePresenter#activityPaused()}
 * and {@link PauseAndResumePresenter#activityResumed()} at the obvious times.
 */
public interface PauseAndResumeActivity {
  boolean isRunning();

  MortarScope getMortarScope();
}

And have it inject the presenter and make the appropriate calls:

private boolean resumed;
@Inject PauseAndResumePresenter pauseNarcPresenter;

@Override protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  pauseNarcPresenter.takeView(this);
}

@Override public boolean isRunning() {
  return resumed;
}

@Override protected void onResume() {
  super.onResume();
  resumed = true;
  pauseNarcPresenter.activityResumed();
}

@Override protected void onPause() {
  resumed = false;
  super.onPause();
  pauseNarcPresenter.activityPaused();
}

@Override protected void onDestroy() {
  pauseNarcPresenter.dropView(this);
  super.onDestroy();
}

Now interested parties can inject a registrar interface to opt-in to pause and resume calls, without subclassing anything.

/**
 * Provides means to listen for {@link android.app.Activity#onPause()} and {@link
 * android.app.Activity#onResume()}.
 */
public interface PauseAndResumeRegistrar {
  /**
   * <p>Registers a {@link PausesAndResumes} client for the duration of the given {@link
   * MortarScope}. This method is debounced, redundant calls are safe.
   *
   * <p>Calls {@link PausesAndResumes#onResume()} immediately if the host {@link
   * android.app.Activity} is currently running.
   */
  void register(MortarScope scope, PausesAndResumes listener);

  /** Returns {@code true} if called between resume and pause. {@code false} otherwise. */
  boolean isRunning();
}

Have the client presenter implement this interface:

/**
 * <p>Implemented by objects that need to know when the {@link android.app.Activity} pauses
 * and resumes. Sign up for service via {@link PauseAndResumeRegistrar#register(PausesAndResumes)}.
 *
 * <p>Registered objects will also be subscribed to the {@link com.squareup.otto.OttoBus}
 * only while the activity is running.
 */
public interface PausesAndResumes {
  void onResume();

  void onPause();
}

And hook things up like this. (Note that there is no need to unregister.)

private final PauseAndResumeRegistrar pauseAndResumeRegistrar;

@Inject
public Presenter(PauseAndResumeRegistrar pauseAndResumeRegistrar) {
  this.pauseAndResumeRegistrar = pauseAndResumeRegistrar;
}

@Override protected void onEnterScope(MortarScope scope) {
  pauseAndResumeRegistrar.register(scope, this);
}

@Override public void onResume() {
}

@Override public void onPause() {
}

Here's the presenter that the activity injects to make it all work.

/**
 * Presenter to be registered by the {@link PauseAndResumeActivity}.
 */
public class PauseAndResumePresenter extends Presenter<PauseAndResumeActivity>
    implements PauseAndResumeRegistrar {

  private final Set<Registration> registrations = new HashSet<>();

  PauseAndResumePresenter() {
  }

  @Override protected MortarScope extractScope(PauseAndResumeActivity view) {
    return view.getMortarScope();
  }

  @Override public void onExitScope() {
    registrations.clear();
  }

  @Override public void register(MortarScope scope, PausesAndResumes listener) {
    Registration registration = new Registration(listener);
    scope.register(registration);

    boolean added = registrations.add(registration);
    if (added && isRunning()) {
      listener.onResume();
    }
  }

  @Override public boolean isRunning() {
    return getView() != null && getView().isRunning();
  }

  public void activityPaused() {
    for (Registration registration : registrations) {
      registration.registrant.onPause();
    }
  }

  public void activityResumed() {
    for (Registration registration : registrations) {
      registration.registrant.onResume();
    }
  }

  private class Registration implements Scoped {
    final PausesAndResumes registrant;

    private Registration(PausesAndResumes registrant) {
      this.registrant = registrant;
    }

    @Override public void onEnterScope(MortarScope scope) {
    }

    @Override public void onExitScope() {
      registrations.remove(this);
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;

      Registration that = (Registration) o;

      return registrant.equals(that.registrant);
    }

    @Override
    public int hashCode() {
      return registrant.hashCode();
    }
  }
}