Nested RouterPagerAdapter's not restoring state on rotation

Question

The root controller, which has a RouterPagerAdapter , hosts controller A which has its own RouterPagerAdapter .

Controller A1 is hosted by controller A

[ Root Controller ]
[   A   ] [   B   ]
[A1] [A2]

Upon rotation, Root Controller, A and A1 receive their onSaveInstanceState/onSaveViewState , but neither A nor A1 is receives it onRestoreInstanceState/onRestoreViewState .

Why is this so? What is the correct implementation to ensure that all children will have their state restored?

Answer 1

onSaveViewState will be called, but onRestoreViewState will not be called due to the viewPager.setAdapter(null); line.

The example in Conductor's docs sets the adapter to null when the view is being destroyed.

Override protected void onDestroyView(@NonNull View view) {
    viewPager.setAdapter(null);
    super.onDestroyView(view);
  }

Because of this, RouterPagerAdapter will call configureRouter to which the router does not have a root controller, and will new Cont()

if (!router.hasRootController()) {
      router.setRoot(RouterTransaction.with(new Cont()));
    }

Also note, when nesting a viewPager within another, both should have unique ids, else on rotation will overwrite the save state of the parent viewPager , and will show the wrong current item.