ViewPager invalidate ActionBar

ViewPagerInvalidateActionBar.java

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
      invalidateActionbar(position);
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
});

private void invalidateActionbar(int position) {
  Fragment currentPage = getChildFragmentManager().findFragmentByTag("android:switcher:" + R.id.viewpager + ":" + viewPager.getCurrentItem());
  if (currentPage == null || currentPage.getView() == null) {
      return;
  }

  Toolbar toolbar = (Toolbar) currentPage.getView().findViewById(R.id.toolbar);
  if (toolbar == null) {
      return;
  }

  ((AppCompatActivity) getActivity()).setSupportActionBar(toolbar);
  for (int i=0; i<viewPagerAdapter.getCount(); i++) {
      Fragment fragment = getChildFragmentManager().findFragmentByTag("android:switcher:" + R.id.viewpager + ":" + i);
      fragment.setHasOptionsMenu(i == position);
  }

  getActivity().invalidateOptionsMenu();
}