Android ViewPager FragmentStatePagerAdapter问题

Question

I'm building an app that uses a Viewpager with a FragmentStatePagerAdapter. The FragmentStatePagerAdapter gets an array of objects witch is later used to map each object data to a fragment.

The adapter loads 3 fragments into memory (onCreateView is called 3 times when I'm on a page), it loads the current fragment and the next two.

I have the following issue:

I must change the content of the next fragment based on content change in the current fragment I'm in.

I've tried to modify the array in the FragmentStatePagerAdapter and then call notifydatasetchanged on the adapter, but the adapter doesn't load again the next page.

what is the best way to pull this off?

some code and scenario: the current fragment I am on contains users data, the logged user can follow him or unfollow.

here is the onClick code:

if(mListener!=null)
                        mListener.onTweetUserFollowingStatusChanged(tweet.getUser());

the callback from listener in the activity with the viewpage:

@Override
    public void onTweetUserFollowingStatusChanged(User user) {
        DataManager.getInstance().onTweetUserFollowStatusChanged(user);
        List<Tweet> affectedTweets = mPagerAdapter.getTweetsWithUser(user);
        for (Tweet affectedTweet: affectedTweets
                ) {
            boolean affectedTweetCurrentUserFollowStats = affectedTweet.isFollowingTweetUser();
            affectedTweet.setFollowingTweetUser(!affectedTweetCurrentUserFollowStats);
        }
        mPagerAdapter.notifyDataSetChanged();
    }

The next page containes the same user.

So if I follow him on the curent page I want the follow button from the next page to display "UNFOLLOW"

Answer 1

I have found the solution;

Original problem:

after updating the array in the FragmentStateAdapter I needed a way to update the UI of the already instantiated fragments in the Adapter.

So I after updating the array in the FragmentStateAdapter just call notifyDataSetChange() and add this code to your adapter.

  mPagerAdapter.registerDataSetObserver(new DataSetObserver() {
            @Override
            public void onChanged() {
                super.onChanged();

                FragmentStatePagerAdapter fragmentPagerAdapter = (FragmentStatePagerAdapter) VP_tweets.getAdapter();
                for(int i = 0; i < fragmentPagerAdapter.getCount(); i++) {
                    TweetFragment viewPagerFragment = (TweetFragment) VP_tweets.getAdapter().instantiateItem(VP_tweets, i);
                    if(viewPagerFragment != null && viewPagerFragment.isAdded()) {
                        viewPagerFragment.updateUI();
                    }
                }
            }

        });