ActionBar owner in Mortar - mortar

Question

In Mortar, I'm curious how people are handling the ActionBar if it changes based on the screen being shown. Say, for instance, that you want to change the ActionBar title or actions if a certain screen is being shown.
Injecting an Activity seems like a terrible idea, and you want a presenter (or view, I suppose) to be able to get the correct action bar after screen rotation.
Is there a particularly effective pattern here that I'm missing? All the solutions I had work, but are more awkward than I hoped.

Answer 1

For actions, the flow-sample application's MainActivity includes:
public boolean onCreateOptionsMenu(Menu menu) {
...
Object screen = AppFlow.get(this).getBackstack().current().getScreen();
...
public void go(Backstack nextBackstack, Flow.Direction direction, Flow.Callback callback)
Screen screen = (Screen) nextBackstack.current().getScreen();
...
Both methods are aware of the screen to be displayed. The actions are defined in onCreateOptionsMenu(), the title in go(). The issue is that all this is located in the MainActivity.
What you could do is create a ActionEnabledScreen interface with a method:
public boolean onCreateOptionsMenu(Menu menu);
And a TitleEnabledScreen interface with a method:
public void getTitle();
Your activity would then look like this:
public boolean onCreateOptionsMenu(Menu menu) {
...
Object screen = AppFlow.get(this).getBackstack().current().getScreen();
if (screen instanceof ActionEnabledScreen) {
return ((ActionEnabledScreen)screen).onCreateOptionsMenu(menu);
}
...
public void go(Backstack nextBackstack, Flow.Direction direction, Flow.Callback callback)
Screen screen = (Screen) nextBackstack.current().getScreen();
if (screen instanceof TitleEnabledScreen) {
setTitle(((TitleEnabledScreen)screen).getTitle());
}
...
Note that I didn't run the above code, so it might not compile / run, but I hope you see the idea. The aim is to avoid having MainActivity expand linearly as you implement new screens, and avoid at all costs having to reference you screen classes directly in it.
Hope this helps!