Passing Data Between Two Fragments In A VIewPager (Android) (NullPointerException)

So basically I have 2 Fragments - FragmentConverter and FragmentFavourites, and I have one MainActivity. I'm trying to pass 4 arrays from the first fragment to the second one using

Solution 1:

EDITED:

When you call fragmentPagerAdapter.getItem(1) you are getting a new instance of the fragment so you are referring to a different object. this is why the view is null and you get the NullPointerException. If you need an adapter for only 2 fragments, you can try with something like that:

public class YourPagerAdapter extends android.support.v4.app.FragmentPagerAdapter {

        private FragmentFavourites mFragFavourites;
        private FragmentConverter mFragConverter;

        public YourPagerAdapter() {

            // ... your code above
            this.mFragFavourites = new FragmentFavourites();
            this.mFragConverter = new FragmentConverter();
        }

        @Override
        public Fragment getItem(int position) {

            switch (position) {
                case 0:  
                    return mFragFavourites;

                case 1:
                    return mFragConverter;                      
                default:
                    return null;
            }    
        }
    }

Solution 2:

As above carlo.marinangeli has suggested when you call fragmentPagerAdapter.getItem(1) you are getting a new instance of the fragment so you are referring to a different object

So to get same object from you adapter you need to store your object. you can try following method in your adapter -

public Fragment getFragmentAtPosition(int position) {
            return registeredFragments.get(position);
}

where registeredFragments is -

private SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();

and fill this sparseArray in getItem method like below -

@Override
        public Fragment getItem(int position) {
            switch (position) {
                case 0:
                    fragment = FragmentPost.newInstance(position);
                    registeredFragments.put(position, fragment);
                    return fragment;
               }
            return null;
        }

Solution 3:

By using fragmentPagerAdapter.getItem(pos) method I was referring to a new object every time the respond() method was called. I fixed it by using findFragmentByTag() method instead:

    @Override
    public void respond(String[] names, String[] codes, String[] symbols,
            int[] images) {
        FragmentManager manager = getSupportFragmentManager();
        FragmentConverter frag = (FragmentConverter) manager.findFragmentByTag("android:switcher:" + pager.getId() + ":" + 1);
        frag.changeData(names, codes, symbols, images);
    }

Solution 4:

you can get that error because you are assuming that you have got the FragmentConverter and the views associated to it.

Without a logcat it becomes a little bit difficult to help you but basically what I would like to do in a situation like this is to pass everything through the activity without letting know the existence of the other fragment to the fragments.

• F1 modifies a state object into the activity
• F2 has to register as a listener to the activity (be aware that the fragment can be attached and detached in the view pager)
• The Activity as soon it receives an updated, looks for all the registered listeners and if there is someone it delivers the updated