RecyclerView + ViewPager NullPointerException on 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()'

Question

I have an activity extending AppCompatActivity with a single fragment which contains RecyclerView. On any item click, it will replace this fragment with another fragment which contains ViewPager and fragments of ViewPager are again RecyclerView.

RecyclerViewFragment
ViewPagerFragment

I am getting following error(app crashes) on ViewPager fragment while scrolling the page.

E/InputEventReceiver: Exception dispatching input event. E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback E/MessageQueue-JNI: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()' on a null object reference E/MessageQueue-JNI: at android.support.v7.widget.RecyclerView.onInterceptTouchEvent(RecyclerView.java:2022) E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2059) E/MessageQueue-JNI: at android.view.ViewGroup.dispatchTransformedTouchEvent
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E/AndroidRuntime: FATAL EXCEPTION: main E/AndroidRuntime: Process: me.twig.twigme, PID: 23451 E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()' on a null object reference E/AndroidRuntime: at android.support.v7.widget.RecyclerView.onInterceptTouchEvent(RecyclerView.java:2022) E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2059) E/AndroidRuntime: at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2432) E/AndroidRuntime: at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2119)

Below is the code RecyclerViewFragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_cards, container, false);
}

@Override
public void onResume() {
    super.onResume();

    cardsRecyclerView = (RecyclerView) getActivity().findViewById(R.id.cards_recycler_view);
    final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
    layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    cardsRecyclerView.setLayoutManager(layoutManager);

    if(cardsRecyclerView.getAdapter() == null)
    {
        cardAdapter = new CardAdapter(getActivity().getApplicationContext(), getActivity(), new ArrayList<CardModel>());
        cardsRecyclerView.setAdapter(cardAdapter);
    }
    // List initialization code 
}

public static RecyclerViewFragment createInstance(String cardsJson) {

        RecyclerViewFragment cardsListFragment = new RecyclerViewFragment();
        Bundle args = new Bundle();
        args.putString("cardsJson", cardsJson);
        cardsListFragment.setArguments(args);
        return cardsListFragment;
}

ViewPagerFragment

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_cards_pager, container, false);
}

@Override
public void onStart() {
    super.onStart();

    tabLayout = (TabLayout) getActivity().findViewById(R.id.tabLayout);
    tabLayout.removeAllTabs();

    viewPager = (ViewPager) getActivity().findViewById(R.id.viewPager);
    pagerAdapter = new PagerAdapter(getChildFragmentManager());

    for( i=0; i<3; i++)
    {
        pagerAdapter.addFragment(RecyclerViewFragment.createInstance(cardsJson), "Tab title");
    }

    viewPager.setAdapter(pagerAdapter);
    tabLayout.setupWithViewPager(viewPager);
}

class PagerAdapter extends FragmentStatePagerAdapter {

        private final List<Fragment> fragmentList = new ArrayList<>();
        private final List<String> fragmentTitleList = new ArrayList<>();

        public PagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
            fragmentList.clear();
            fragmentTitleList.clear();
        }

        public void addFragment(Fragment fragment, String title) {
            fragmentList.add(fragment);
            fragmentTitleList.add(title);
        }

        @Override
        public Fragment getItem(int position) {
            return fragmentList.get(position);
        }

        @Override
        public int getCount() {
            return fragmentList.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return fragmentTitleList.get(position);
        }

        @Override
        public int getItemPosition(Object object) {
            return POSITION_NONE;
        }
}

fragment_cards.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_frame_layout"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/cards_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/ColorPrimaryLight"
        android:clipToPadding="false"
        xmlns:android="http://schemas.android.com/apk/res/android" />
</FrameLayout>

fragment_cards_pager.xml

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:id="@+id/coordinatorLayout"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
    android:background="@color/ColorPrimaryLight">

    <android.support.design.widget.AppBarLayout
            android:id="@+id/appBarLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
        <android.support.design.widget.TabLayout
                android:id="@+id/tabLayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:tabTextColor="@android:color/white"
                app:tabSelectedTextColor="@android:color/white"
                app:tabIndicatorColor="@android:color/white"
                app:tabIndicatorHeight="6dp"/>
    </android.support.design.widget.AppBarLayout>

    <ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
</android.support.design.widget.CoordinatorLayout>

i am also stuck on this :( kindly update the post if you found any answer..!! — mfaisalhyder, Jan 27 '16 at 10:04

score 4 · Answer 1 · edited May 23 '17 at 10:30

From aga's answer

This issue usually occurs when no LayoutManager was provided for the RecyclerView. You can do it like so:
final LinearLayoutManager layoutManager = new LinearLayoutManager(context);
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(layoutManager);

This solution is done programatically, but it means that you don't have any LayoutManager declared inside the RecyclerView.

score 0 · Answer 2 · answered May 06 '16 at 19:10

Essentially, the given exception comes when the LayoutManager is not set on the RecyclerView.

I think your problem lies in following lines :

for( i=0; i<3; i++)
{
   pagerAdapter.addFragment(RecyclerViewFragment.createInstance(cardsJson), "Tab title");
}

Using the same fragment in all three adjacent views is causing errors on swiping as ViewPager maintains the adjacent view states for swiping behavior. Use of same ids is also known to have cause similar problems. Try checking by rendering distinct fragments.

Also, displaying the same fragment in all the tabs doesn't look logical.

RecyclerView + ViewPager NullPointerException on 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()'

2 Answers2