How to resolve a NullPointerException while using RecyclerView?

Question

I am using two RecyclerViews in my app, one in the MainActivity and one in another activity. The one in the MainActivity works fine but the other has a NullPointerException and I don't know where the problem here is.

Here is a code snippet of the second RecyclerView, where the logcat says that there is a Null object reference. I used the same code as the first RecyclerView where everything works.

The error message says that there is a problem in this line: recyclerView.setLayoutManager(layoutManager);

and in this line initRecyclerViewFriendOverView();

Here is where I implemented my second RecyclerView:

private void initRecyclerViewFriendOverView() {

        LinearLayoutManager layoutManager = new LinearLayoutManager(this, RecyclerView.VERTICAL, false);
        RecyclerView recyclerView = findViewById(R.id.recyclerViewFriendOverView);
        recyclerView.setLayoutManager(layoutManager);
        RecyclerViewAdapterFriendOverView adpater = new RecyclerViewAdapterFriendOverView(mNames, mImageUrls, this);
        recyclerView.setAdapter(adpater);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_play_overview);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        init();
        initRecyclerViewFriendOverView();
        getImages();
    }

Here ist the XML where the second RecyclerView is used:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerViewFreundesUebersicht"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:orientation="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

Edit:

The problem was that I called the RecyclerView before initializing it in the onCreate method.

The logcat report will give you the exact line where the code issues out. Please check it out or post it. — defvs Daniel, Aug 03 '19 at 11:36
I wrote in the description where the Logical says is a problem but I don't know what to change there — Kaiser, Aug 03 '19 at 11:48
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — a_local_nobody, Aug 03 '19 at 11:50
Please [edit] your question to provide additional code or XML. Please don't post it in comments. — Mike M., Aug 03 '19 at 12:37

score 1 · Answer 1 · answered Aug 03 '19 at 11:52

Initialize LinearLayoutManager like this

  LinearLayoutManager linearLayoutManager = new LinearLayoutManager(context);
    linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(linearLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());

score 1 · Accepted Answer · edited Aug 10 '19 at 20:41

1

EDIT:

You are including another xml file in your activity using include statement, findViewById() won't be able to find views from included layouts. Give an id to your include statement, find that included view first and then call findViewById () in that view:

In Activity layout file:

<include id="includedRecyclerLayout"
....
</include>

And in your code:

ConstraintLayout includedLayout = findViewById(R.id.inckudedRecyclerLayout);

RecyclerView recyclerview = includedLayout.findViewById(R.id.RECYCLER_VIEW_ID);

If it shows error at recyclerView.setLayoutManager(layoutManager); it means your recyclerView is null. Then you look at where you initialized it:

RecyclerView recyclerView = findViewById(R.id.recyclerViewFreundesUebersicht);

It can be null because of two reasons:

You didn't add the RecyclerView to XML
Your R.id.recyclerViewFreundesUebersicht is referring to a view from another xml

Check your XML and make sure your recyclerview was added to XML and the id you are using here is same as the one used in activity.

edited Aug 10 '19 at 20:41

marc_s

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answered Aug 03 '19 at 11:52

Zohaib Amir

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Thank you for your help. I added a RecyclerView to the XML otherwise it would display a different error and also the R.id is referring to the right view – Kaiser Aug 03 '19 at 13:02
@Kaiser can you post the layout file? – Zohaib Amir Aug 03 '19 at 13:43
I edited my question with additional information, I hope you can find a solution with these information, I appreciate your assistance – Kaiser Aug 04 '19 at 09:39
@Kaiser what are the names of layout files of both activities? – Zohaib Amir Aug 04 '19 at 10:26
The first is app_bar_main.xml with the RecyclerView id recyclerViewAktuelleSpiele and the second is freundesUebersicht.xml with the RecyclerView id recyclerViewFreundesUebersicht – Kaiser Aug 04 '19 at 11:05
@Kaiser check your `setContentView()` and see if you provided the right layout id – Zohaib Amir Aug 04 '19 at 11:08
@Kaiser found your problem, are you including a separate layout file in your xml? – Zohaib Amir Aug 04 '19 at 11:09
Ok I figured it out, I had the RecyclerView in the wrong Java class – Kaiser Aug 04 '19 at 11:15

How to resolve a NullPointerException while using RecyclerView?

2 Answers2