Set child fragment's ViewPager page from Activity

Question

I have a fragment with a ViewPager ( fragment_main ) inside my MainActivity . On my MainActivity I have a BottomNavigationView . I want to set the fragment_main 's ViewPager ' page when I click the items of BottomNavigationView . how can I do that?

PS: I already made it work but I don't think I used a good way.I got a refrence to my ViewPager inside my fragment and I set the Item:

 bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            MainFragment mainFragment = null;
            switch (item.getItemId()){
                case R.id.nav_item_feed:
                    mainFragment =(MainFragment)getSupportFragmentManager().findFragmentById(R.id.main_frame);
                    mainFragment.viewPager.setCurrentItem(0);
                    break;
            }
        }

It works! But the problem is: what if I have another fragment on my MainActivity ? Sure, I can replace it with fragment_main first but it takes time and mainFragment =(MainFragment)getSupportFragmentManager().findFragmentById(R.id.main_frame) returns null.

So whats the best way to set fragment's viewpager's page, Inside parent activity?

Answer 1

Use FrameLayout instead of ViewPager for Fragments

Use below line in your case statement inside bottomNavigationView click listener.

toFrag(ProductsFrag.newInstance(FragInstance.PRODUCTS));

    public void toFrag(Fragment toFrag){
    new Handler().postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            getSupportFragmentManager().beginTransaction().replace(R.id.content, toFrag).commitAllowingStateLoss();
                        }
                    }, 200);
}

here R.id.conent is FrameLayout id