Dynamically changing fragment contents in a ViewPager

Question

I have:

• A ViewPager with a FragmentPagerAdapter on (or a FragmentStatePagerAdapter, doesn't really solve my problem).
• A fixed number of fragments. They all share the same layout, but have TextViews that need to be set differently;
• An AsyncTask that queries my database and retrieves content to be set into the TextViews.

So my code was:

public class StatsPagerAdapter extends FragmentPagerAdapter {
    static final int FRAGMENT_COUNT = 5;
    private Parameters[] sectionData;

    public StatsPagerAdapter(FragmentManager manager) {
        super(manager);
        this.sectionData = new Parameters[FRAGMENT_COUNT];
    }

    @Override
    public Fragment getItem(int position) {
        return StatsSectionFragment.getInstance(this.sectionData[position]);
    }

    @Override
    public int getCount() {
        return FRAGMENT_COUNT;
    }

    public void setSectionData(int position, Parameters sectionData) {
        this.sectionData[position] = sectionData;
        notifyDataSetChanged();
    }
}

So I'm passing sectionData[position] to the getInstance() method of my generic sub-fragment. That data should differentiate each instance of the fragments loaded into the ViewPager.

At first I'll be passing an empty reference, but then in my async class:

    @Override
    protected void onProgressUpdate(Parameters... sectionValues) {
        super.onProgressUpdate(sectionValues);
        mPagerAdapter.setSectionData(sectionId, sectionValues[0]);
    }

That should call the setSectionData() above, update sectionData[position] and generate a call to notifiyDataSetChanged(). I was hoping that doing so would make the adapter retrieve all its items again, thus calling getItem() again, and loading new fragments.

Sadly it does not. So right now:

• if fragments (i.e., getItem()) are created before my async task result are published, that item will stay empty (i.e.,visible fragment, but with empty text views since I never called getInstance(non-null stuff). That happens for fragment 0 && fragment 1.

• if fragments are created after my async task has ended (fragment 2 to end, because getItem() is called only when you reach that fragment by swiping), then the first and only call to getItem() produces a getInstance(non-null stuff), and that's ok.

How can I reload content into those already-there fragments, or force the adapter to call getItem() and update its views?

Answer 1

Add this to your adapter:

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

This make your adapter call getItem again when you call notifyDataSetChanged();