How do I reference a certain fragment from my ViewPager

Question

So I'm trying to communicate between 2 fragments which are organized in a ViewPager (Swipe-tab) by using an interface I created. Like this:

The interface looks like this:

    public interface Communicator {
        public void respond(String data);
    }

On Fragment A I reference the interface calling it 'comm', the onClick of FragmentA looks like this:

    comm = (Communicator) getActivity();
    comm.respond("String being passed");

However - when I go back to my main activity in the respond override method I try to reference my fragment and I get the nullPointer exception:

    FragmentManager manager = getSupportFragmentManager();
    FragmentB fragB = (FragmentB) manager.findFragmentById(R.id.fragmentB);

Maybe I declared the ID of the fragment in the wrong way in the XML file ? I'm a beginner so I scour the net but I'm not really sure what is it that I'm looking for, any directions will also be nice

thanks in advance

Add your xml files and LogCat please – Marcus Feb 16 '15 at 14:51 — Marcus, Feb 16 '15 at 14:51

score 0 · Answer 1 · edited May 23 '17 at 11:43

So I solved it, my problem was as @CurlyCorvus said.

To get the Id of the Fragment while using ViewPager I used this solution: Retrieve a Fragment from a ViewPager

Basically it says to Override 2 more methods to your custom adapter like this and adding another method to get the items as fragments:

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

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}
public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

And in my method I reference my fragments like this:

 FragmentB fragB = (FragmentB) ((myAdapter) viewPager.getAdapter()).getRegisteredFragment(1);

My fragment is no longer null, and the interface is working and I can pass along data between my two fragments, thanks for your help

How do I reference a certain fragment from my ViewPager

1 Answers1