重新启动ViewPager + FragmentStatePagerAdapter到项目0

Question

Using SDK 19, min 13, and support.v4.app Fragments.

I have searched SO and found similiar threads which should help, but everything I have tried has not addressed my issue yet. Furthermore, many people seem to have the issue of the ViewPager restarting when they don't want it to, whereas my problem seems to be the opposite.

These posts do not seem to have helped me yet:
PagerAdapter start position
ViewPager PagerAdapter not updating the View
How to force ViewPager to re-instantiate its items

Here is my setup:
A (support.v4) Fragment in memory, which contains a ViewPager, inflated from a layout file, thus not added programmatically. The Fragment itself is not recreated, but in memory for the life of the app; it is being attached/detached to the root FragmentActivity's FragmentManager.

When the user visits this Fragment sometime during the app's lifetime, it is attached and the onCreateView is called, where I findViewById the ViewPager and assign a new FragmentStatePagerAdapter to it.

Here is my problem:
The first time the user visits this pager, everything works fine. The next time they visit it, I expect it to "start over" from page 0, meaning that I expect to not be able to scroll left immediately, but must start scrolling right. I also expect the getItem() of the FragmentStatePagerAdapter to start back at position 0. I basically want it to function the same as the first time the user visited it. However, this is not the case.

I have tried several things, but it always seems to start at the previous index of page I left it at. So if the first time I scrolled 5 pages over, and then left the Fragment and returned later, the ViewPager starts at that same page index, meaning I can scroll 5 pages left. I don't want this.

It may have something to do with the ViewPager or FragmentStatePagerAdapter storing pages internally, which are not being released. But I thought the commented out code I tried would have done that. There might be another way that I have not tried. Perhaps it is related to not recreating my Fragment, but doing so at this point in my architecture will not be great. I was hoping I could restart the ViewPager without doing this.

Here is my code:

My Fragment's onCreateView code. Everything commented out I have tried without success.

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    View view = inflater.inflate(R.layout.fragment_playscreen, container, false);

    //while (getChildFragmentManager().popBackStackImmediate()) {}

    mAdapter = new AdapterPlayPages(this, getChildFragmentManager());
    mPager = (ViewPlayPager) view.findViewById(R.id.pagerPlayScreen);
    //mPager.setAdapter(null);
    mPager.storeAdapter(mAdapter);
    //mPager.setCurrentItem(0);
    //mPager.removeAllViews();

    return view;
}

My ViewPager, which has been overridden like so to get around a completely unrelated bug, as suggested here: https://stackoverflow.com/a/19900206/1002098 . This does not effect the problem; I removed these changes so that I could call setAdapter(null) as suggested, but it did not address my question.

public class ViewPlayPager extends ViewPager
{
    PagerAdapter mPagerAdapter;

    public ViewPlayPager(Context context)
    {
        super(context);
    }

    public ViewPlayPager(Context context, AttributeSet attrs)
    {
        super(context, attrs);
    }

    @Override
    protected void onAttachedToWindow()
    {
        super.onAttachedToWindow();

        if (mPagerAdapter != null)
        {
            //super.setAdapter(null);  // did not help
            super.setAdapter(mPagerAdapter);
        }
    }

    @Override
    public void setAdapter(PagerAdapter adapter)
    {
        // do nothing
    }

    public void storeAdapter(PagerAdapter adapter)
    {
        mPagerAdapter = adapter;
    }
}

My FragmentStatePagerAdapter. I've removed some unrelated logic and members.

public class AdapterPlayPages extends FragmentStatePagerAdapter
{
    private FragmentPlayScreen mParent;

    public AdapterPlayPages(FragmentPlayScreen parent, FragmentManager fragmentManager)
    {
        super(fragmentManager);

        mParent = parent;
    }

    @Override
    public int getCount()
    {
        // some logic from parent to determine true count
        // the count shouldn't effect the position to start at

        return Integer.MAX_VALUE;
    }

    @Override
    public Fragment getItem(int position)
    {
        // logic to determine type of page to display,
        // which is not changing based on position at the moment

        return new FragmentPlayPage();
    }

    // this did not seem to help me
    //@Override
    //public int getItemPosition(Object object)
    //{
    //     //return super.getItemPosition(object);
    //    return POSITION_NONE;
    //}
}

Answer 1

I had to change my architecture to recreate the Fragments - add/remove them from FragmentManager, as opposed to attach/detach them while kept in memory.

It is not clear to me why the Fragment would have to be recreated for the ViewPager to reset. Android FragmentManager and FragmentTransaction supports keeping Fragments in memory and simply attaching/detaching them, or showing/hiding them, so it should be possible to simply reset the ViewPager from the in-memory Fragment's onCreateView event, but again, none of the commented out calls above seemed to work.

If anyone else has a solution, I'd still consider it. It will help me understand this issue.