Getting Null Pointer Exception - Using an Interface to Pass Data from an Adapter to a Sub-fragment

Question

I have an

Adapter

and a

Sub-Fragment

. I am using an interface to pass data from the

Adapter

to the

Sub-Fragment

. The problem I am having is that I keep getting a

Null Pointer Exception

. I have read through the various posts here relating to the problem and can't figure out where I went wrong. I get the NPE at the line 'passAdapterVariable.passAdapterVariable(mname)'. Based on what I have read I suspect it may be because I am not properly initializing passAdapterVariable. I have tried initializing it several different ways based on other examples but I keep getting the NPE.

Here is the Adapter

public class MatchAdapter extends RecyclerView.Adapter<MatchAdapter.MatchViewHolder> {



    //declaration of variables

    private Fragment fragment;

    private FragmentManager fragmentManager;

    private DiscoverPage discoverPage;

    private Context context;

    private int size;

    private int mposition;

    private TextView txt_matchname;

    private ImageView img_matchpic;

    List<String> maImg = new ArrayList<>();

    private String mname;

    PassAdapterVariable passAdapterVariable;





    public interface PassAdapterVariable {



        void passAdapterVariable(String mname);

    }





    //the constructor

    public MatchAdapter(List<String> maImg, int size, Context context, DiscoverPage discoverPage){//, PassAdapterVariable passAdapterVariable) {



        this.maImg = maImg;

        this.context = context;

        this.discoverPage = discoverPage;

        this.size = size;

        //this.passAdapterVariable = (PassAdapterVariable)context;

    }



    public MatchAdapter(String mname, Context context) {

        this.context = context;

        this.passAdapterVariable  = (PassAdapterVariable)context;

    }





    //PassAdapterVariable passAdapterVariable = (PassAdapterVariable) context;





    @Override

    public MatchAdapter.MatchViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.match_items, parent, false);

        MatchViewHolder matchViewHolder = new MatchViewHolder(view, maImg, discoverPage);





        return matchViewHolder;

    }





    @Override

    public void onBindViewHolder(MatchViewHolder holder, int position) {



        Picasso.with(context).load(maImg.get(position)).into(holder.img_match);

        holder.setIsRecyclable(false);



    }





    @Override

    public int getItemCount() {

        return maImg.size();

    }





    //viewholder class

    public class MatchViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {



        private static final String TAG = "error";

        //declare variables

        private DiscoverPage discoverPage;

        private ImageView img_match;





        //ViewHolder constructor

        public MatchViewHolder(View itemView, final List<String> maImg, final DiscoverPage discoverPage) {

            super(itemView);



            //initialize variables inside the viewholder constructor

            this.discoverPage = discoverPage;

            img_match = (ImageView) itemView.findViewById(R.id.img_match);

            txt_matchname = (TextView) itemView.findViewById(R.id.txt_matchname);

            img_matchpic = (ImageView) itemView.findViewById(R.id.img_matchpic);





            //set click listener for the img_match

            img_match.setOnClickListener(this);



        }





        @Override

        public void onClick(View view) {

            if (view == img_match) {

                //discoverPage.isHidden();

                Fragment currentFragment;

                fragment = new ClickedMatch();

                fragmentManager = ((AppCompatActivity) context).getSupportFragmentManager();

                FragmentTransaction transaction = fragmentManager.beginTransaction();

                transaction.replace(android.R.id.content, fragment);

                transaction.addToBackStack("DiscoverPage");



                if ((currentFragment = ((AppCompatActivity) context).getSupportFragmentManager().findFragmentById(R.id.main_container)) != null) {

                    transaction.hide(currentFragment);

                }

                else {

                    transaction.commit();

                }





                mname = maImg.get(getAdapterPosition());

                mposition = getAdapterPosition();

                mname = maImg.get(mposition);

                passAdapterVariable.passAdapterVariable(mname);



            }



        }

    }

}

Here is the Sub-Fragment

public class ClickedMatch extends Fragment implements MatchAdapter.PassAdapterVariable{



    //declare variables

    private Toolbar toolbar;

    private TextView txt_matchname;

    private TextView txt_matchprice;

    private ImageView img_matchpic;

    private String mname;

    private String imgmatch;

    List<String> maImg = new ArrayList<>();

    int size;

    Context context;

    DiscoverPage discoverPage;

    private String pname;

    private int i;

    MatchAdapter.PassAdapterVariable passAdapterVariable;







    public ClickedMatch() {

        // Required empty public constructor



    }



    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        View view = inflater.inflate(R.layout.fragment_clicked_match, container, false);



        //initialize variables

        toolbar = (Toolbar) view.findViewById(R.id.toolbar);

        ((AppCompatActivity)getActivity()).setSupportActionBar(toolbar);//set toolbar as action bar

        txt_matchname = (TextView)view.findViewById(R.id.txt_matchname);

        img_matchpic = (ImageView)view.findViewById(R.id.img_matchpic);



        //setHasOptionsMenu(true);



        toolbar.setNavigationOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                getActivity().onBackPressed();

            }

        });



        if(((AppCompatActivity)getActivity()).getSupportActionBar()!= null){

            ((AppCompatActivity) getActivity()).getSupportActionBar().setDisplayHomeAsUpEnabled(true);

            ((AppCompatActivity)getActivity()).getSupportActionBar().setDisplayShowHomeEnabled(true);

            ((AppCompatActivity)getActivity()).getSupportActionBar().setHomeButtonEnabled(true);

            ((AppCompatActivity)getActivity()).getSupportActionBar().setTitle("");

        }



       // MatchAdapter matAdapter = new MatchAdapter(maImg, size, context, discoverPage,

        //passAdapterVariable);



       // matAdapter.passAdapterVariable = this;

        //passAdapterVariable.passAdapterVariable(mname);

        //txt_matchname.setText(pname);



        MatchAdapter matAdapter = new MatchAdapter(pname, getContext());

        matAdapter.passAdapterVariable = this;

        passAdapterVariable(pname);

        txt_matchname.setText(pname);



        return view;

    }

    @Override

    public void passAdapterVariable(String mname) {

       this.pname = mname;



    }







    @Override

    public boolean onOptionsItemSelected(MenuItem item) {

        int id = item.getItemId();

        if (id == android.R.id.home) {

            this.getActivity().finish();

        }



       return super.onOptionsItemSelected(item);



    }



}

Here is the error log

08-13 21:53:49.341 12852-12852/com.test.jack E/AndroidRuntime: FATAL EXCEPTION: main

     Process: com.test.jack, PID: 12852



     java.lang.NullPointerException: Attempt to invoke interface method 'void com.test.jack.MatchAdapter$PassAdapterVariable.passAdapterVariable(java.lang.String)' on a null object reference

     at com.test.jack.MatchAdapter$MatchViewHolder.onClick(MatchAdapter.java:138)

     at android.view.View.performClick(View.java:5637)

     at android.view.View$PerformClick.run(View.java:22429)

     at android.os.Handler.handleCallback(Handler.java:751)

     at android.os.Handler.dispatchMessage(Handler.java:95)

     at android.os.Looper.loop(Looper.java:154)

     at android.app.ActivityThread.main(ActivityThread.java:6119)

     at java.lang.reflect.Method.invoke(Native Method)

     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)

     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

To add some more context, I have a main activity(UserMainPage). A bottom navigation menu selector replaces the UserMainPage with a fragment(DiscoverPage).

DiscoverPage calls the adapter(MatchAdapter). A button click on DiscoverPage replaces DiscoverPage with a sub-fragment(ClickedMatch).

I am trying to pass a variable from MatchAdapter to ClickedMatch.

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Answer 1

I was able to find a solution with no help from those who commented or provided insight to this question and had only served to demonstrate their ineptness and waste my time.

I was able to pass data from an adapter to a sub-fragment using a Bundle.

I modified my code as follows:

In the adapter I added:

fragment = new ClickedMatch();
Bundle bundle = new Bundle();
bundle.putString("matchname",mname);
fragment.setArguments(bundle); 

...

transaction.commit();

In my sub-fragment I added:

Bundle bundle = this.getArguments();
if(bundle != null){
   pname = bundle.getString("matchname");
}

There was no need to use an interface. Based on what I have researched I think (and I may be wrong) that creating an interface and then implementing it is better used when communicating between fragments as opposed to communicating between an adapter and a sub-fragment.

Getting Null Pointer Exception - Using an Interface to Pass Data from an Adapter to a Sub-fragment

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