How to properly handle screen rotation with a ViewPager and nested fragments?

Question

I\'ve got this activity, which holds a fragment. This fragment layout consists of a view pager with several fragments (two, actually).

When the view pager is created, it

Answer 1

The problem is that getItem() in FragmentPageAdapter has a wrong name. It should have been named createItem(). Because the way it works the getItem() is for create fragments and it's not safe to call it to query/find a fragment.

My recomendation is to make a copy of current FragmentPagerAdapter and change it that way:

Add:

    public abstract Fragment createFragment(int position);

And change getItem to:

public Fragment getItem(int position) {
    if(containerId!=null) {
        final long itemId = getItemId(position);
        String name = makeFragmentName(containerId, itemId);
        return mFragmentManager.findFragmentByTag(name);
    } else {
        return null;
    }
}

Finally add that to instantiateItem:

    if(containerId==null)
        containerId = container.getId();
    else if(containerId!=container.getId())
        throw new RuntimeException("Container id not expected to change");

Complete code at this gist

I think that this implementation is safer and easier to use and also has same performance from the original adapter from Google engineers.