PagerAdapter.notifyDataSetChanged does not refresh fragments

Question

My Activity contains a ViewPager and it's custom Adapter which extends FragmentStatePagerAdapter. ViewPager contains 3 fragments

Code to remove Fragments from the ViewPager

MainActivity

public void deleteElement(){
    final int currentItem = mViewPager.getCurrentItem();
    mPagerAdapter.removeItem(currentItem);
    mPagerAdapter.notifyDataSetChanged();
}

CustomPagerAdapter

private ArrayList<Item> data;
public void removeItem(int index){
        data.remove(index);
}

when removing the middle Fragment (index 1):

• from data i'm removing the correct item.
• Problem is that i (i guess) Fragment 3 is removed after notifyDataSetChanged and the current Fragment is still the fragment that the user saw and the data that is being loaded is from the SavedInstance bundle

So the end result that the user still see the same Fragment that he tried to remove which is kinda suck for him.

Ideas?

***** EDIT ******

seems like ViewPager2 Features might solve this issue and many other issues as well

Answer 1

Try adding this:

private class MyPagerAdapter extends FragmentStatePagerAdapter {

//... your existing code

    @Override
    public int getItemPosition(Object object){
        return PagerAdapter.POSITION_NONE;
    }

}

Answer 2

You have no choice but to implement PagerAdapter#getItemPosition. Looking at the source that's exactly how ViewPager determines how to update its position, add new fragments or drop dead ones after notifyDataSetChanged. It shouldn't be too hard, you just need to access the state of the passed fragment, and you also need to access the master state in your activity which holds your ordering.

It's also required you implement getItemId to return a consistent ID for each fragment, because they can be reordered.

This is how I handled it in a ViewPager of photos.

    private inner class PhotoPagerAdapter(fm: FragmentManager) : FragmentPagerAdapter(fm) {
    override fun getItem(position: Int): PhotoViewFragment {
        // getItem is called to instantiate the fragment for the given page.
        return PhotoViewFragment.newInstance(position, [email protected][position])
    }

    override fun getItemId(position: Int): Long {
        return [email protected][position].ID!!.hashCode().toLong()
    }

    override fun getItemPosition(`object`: Any): Int {
        val frag = `object` as PhotoViewFragment
        val idx = [email protected] { ph -> ph.ID == frag.dataBinding.photo.ID }
        return if (idx >= 0) idx else PagerAdapter.POSITION_NONE
    }

    override fun getCount(): Int {
        return [email protected]
    }
}