Android List view not working with fragment

Question

I am trying to display a list of image views using a fragment and a Recycler View Adapter.

I get this exception everytime

  Process: com.example.plasmavietiles, PID: 4860
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.recyclerview.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference
        at androidx.recyclerview.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:4311)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4045)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3849)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at com.google.android.material.appbar.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:148)
        at com.google.android.material.appbar.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:43)
        at com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1892)
        at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:918)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:726)
        at android.view.View.layout(View.java:17637)
        at android.view.ViewGroup.layout(ViewGroup.java:5575)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2346)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2068)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
        at android.view.Choreographer.doCallbacks(Choreographer.java:686)
        at android.view.Choreographer.doFrame(Choreographer.java:621)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Here is my code:

QuestionnaireActivity

public class QuestionnaireActivity  extends Activity implements View.OnClickListener, View.OnTouchListener {


    private ArrayList<Integer> questionList;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_questionnaire);

        /*Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);*/
        prepareView();

        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        QuestionFragment question = new QuestionFragment();
        question.setQuestionArray(questionList);
        fragmentTransaction.replace(R.id.questionnaireFragment,question);
        fragmentTransaction.commit();

    }

    @Override
    protected void attachBaseContext(Context base)
    {
        super.attachBaseContext(LocalHelper.wrap(base));
    }


    @SuppressLint("ClickableViewAccessibility")
    private void prepareView()
    {

        this.questionList = new ArrayList<>();
        Random r = new Random();
        int tmp;
        for(int i =0 ;i<5;){
            tmp = r.nextInt((20 - 1) + 1) + 1;
            if(!this.questionList.contains(tmp))
            {
                this.questionList.add(tmp);
                i++;
            }
        }

    }
}

Question Fragment class:

public class QuestionFragment extends Fragment {

    // TODO: Customize parameter argument names
    private static final String ARG_COLUMN_COUNT = "column-count";
    // TODO: Customize parameters
    private int mColumnCount = 1;
    List<Integer> questionArray = new ArrayList<>();

    /**
     * Mandatory empty constructor for the fragment manager to instantiate the
     * fragment (e.g. upon screen orientation changes).
     */
    public QuestionFragment() {

    }

    public void setQuestionArray(List<Integer> questionArray) {
        this.questionArray = questionArray;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);



      /*  if (getArguments() != null) {
            mColumnCount = getArguments().getInt(ARG_COLUMN_COUNT);
        }*/
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_question_list, container, false);

        // Set the adapter
        if (view instanceof RecyclerView) {
            Context context = view.getContext();
            RecyclerView recyclerView = (RecyclerView) view;
            if (mColumnCount <= 1) {
                recyclerView.setLayoutManager(new LinearLayoutManager(context));
            } else {
                recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
            }
            recyclerView.setAdapter(new MyQuestionRecyclerViewAdapter(questionArray));
        }
        return view;
    }
}

My Recycler view Adapter class:

public class MyQuestionRecyclerViewAdapter extends RecyclerView.Adapter<MyQuestionRecyclerViewAdapter.ViewHolder> {

    private final List<Integer> mValues;

    public MyQuestionRecyclerViewAdapter(List<Integer> items) {
        mValues = items;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.fragment_question, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
       // holder.mItem = mValues.get(position);
       // holder.mIdView.setText(mValues.get(position).id);
        holder.mContentView.setImageResource(R.drawable.facebook_icon);
    }

    @Override
    public int getItemCount() {
            return mValues.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final ImageView mContentView;

        public ViewHolder(View view) {
            super(view);
            //mIdView = (TextView) view.findViewById(R.id.item_number);
            mContentView = (ImageView) view.findViewById(R.id.imageView10);
        }
    }
}

Answer 1

May be you might want to swap these layout

Fragment class before

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

Adapter class before

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

Fragment class after

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

Adapter class after

View view = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.fragment_question_l8st, parent, false);

Answer 2

Instead of checking if view is instanceof recyclerview, try finding recyclerview directly by id.

RecyclerView recycler_view = view.findViewById(R.id.recyclerViewId);
Context context = view.getContext();
RecyclerView recyclerView = (RecyclerView) view;
if (mColumnCount <= 1) {
    recyclerView.setLayoutManager(new LinearLayoutManager(context));
} else {
    recyclerView.setLayoutManager(new GridLayoutManager(context, mColumnCount));
}
recyclerView.setAdapter(new MyQuestionRecyclerViewAdapter(questionArray));