Observer pattern for notifying Fragments of a ViewPager to update their views. This will update the current Fragment, as well as the off screen Fragments that are retained.

FragmentObserver.java

public class FragmentObserver extends Observable {
    @Override
    public void notifyObservers() {
        setChanged(); // Set the changed flag to true, otherwise observers won't be notified.
        super.notifyObservers();
    }
}

MyActivity.java

public class MyActivity extends Activity {
    private MyAdapter mPagerAdapter;
    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        setContentView(R.layout.my_activity);
        ViewPager pager = (ViewPager) findViewById(R.id.pager);
        mPagerAdapter = new MyAdapter();
        pager.setAdapter(mPagerAdapter);
    }
    
    private void updateFragments() {
        mPagerAdapter.updateFragments();
    }
}

MyAdapter.java

public class MyAdapter extends FragmentPagerAdapter {
    private Observable mObservers = new FragmentObserver();

    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        mObservers.deleteObservers(); // Clear existing observers.
        Fragment fragment = new MyFragment();
        if(fragment instanceof Observer)
            mObservers.addObserver((Observer) fragment);

        return fragment;
    }

    public void updateFragments() {
        mObservers.notifyObservers();
    }
}

MyFragment.java

public class MyFragment extends Fragment implements Observer {

    /* Fragment related stuff... */

    @Override
    public void update(Observable observable, Object data) {
        View root = getView();
        // Update your views here.
    }
}

Work fine! For notify all fragments remove mObservers.deleteObservers. Work great for me.
For notify with object change your implementation of FragmentObserver:

public class FragmentObserver extends Observable {
    @Override
    public void notifyObservers(object: Object) {
        setChanged(); // Set the changed flag to true, otherwise observers won't be notified.
        super.notifyObservers(object);
    }
}

In Kotlin:

class FragmentObserver : Observable() {

override fun notifyObservers(arg: Any?) {
setChanged(); // Set the changed flag to true, otherwise observers won't be notified.
super.notifyObservers(arg)
}

}