ViewPager does not redraw content, remains/turns blank

Question

We\'re suffering from a very strange issue with ViewPager here. We embed lists on each ViewPager page, and trigger notifyDataSetChanged both on the list adapter and the view

Answer 1

If the ViewPager is set inside a Fragment with a FragmentPagerAdapter, use getChildFragmentManager() instead of getSupportFragmentManager() as the parameter to initialize your FragmentPagerAdapter.

mAdapter = new MyFragmentPagerAdapter(getChildFragmentManager());

Instead of

mAdapter = new MyFragmentPagerAdapter(getSupportFragmentManager());

Answer 2

For me the problem was coming back to the activity after the app process was killed. I am using a custom view pager adapter modified from the Android sources.The view pager is embedded directly in the activity.

Calling viewPager.setCurrentItem(position, true);

(with animation) after setting the data and notifyDataSetChanged() seems to work, but if the parameter is set to false it doesn't and the fragment is blank. This is an edge case which may be of help to someone.

Answer 3

For Kotlin users:

In your fragments; Use childFragmentManager instead of viewPagerAdapter

Answer 4

Tried too many solutions but unexpectedly viewPager.post() worked

 mAdapter = new NewsVPAdapter(getContext(), articles);
    viewPager.post(new Runnable() {
        @Override
        public void run() {
            viewPager.setAdapter(mAdapter);
        }
    });

Answer 5

ViewPager tries to do clever stuff around re-using items, but it requires you to return new item positions when things have changed. Try adding this to your PagerAdapter:

public int getItemPosition (Object object) { return POSITION_NONE; }

It basically tells ViewPager that everything has changed (and forces it to re-instantiate everything). That's the only thing I can think of off the top of my head.

Answer 6

I had a problem with the same symptoms, but a different cause that turned out to be a silly mistake on my part. Thought I'd add it here in case it helps anyone.

I had a ViewPager using FragmentStatePagerAdapter which used to have two fragments, but I later added a third. However, I forgot that the default off screen page limit is 1 -- so, when I'd switch to the new third fragment, the first one would get destroyed, then recreated after switching back. The problem was that my activity was in charge of notifying these fragments to initialize their UI state. This happened to work when the activity and fragment lifecycles were the same, but to fix it I had to change the fragments to initialize their own UI during their startup lifecycle. In the end I also wound up changing setOffscreenPageLimit to 2 so that all three fragments were kept alive at all times (safe in this case since they were not very memory intensive).