App crashing when trying to use RecyclerView on an

问题:

I'm trying to mess with the new RecyclerView and whenever I try to run it, my app immediately crashes. It gives me NullPointerException for trying to access methods from android.support.v7.widget.RecyclerView. I've looked at other posts and saw that most people didn't have compile 'com.android.support:recyclerview-v7:+' but I tried that and it hasn't helped at all. Not really sure what to do at this point, any help would be appreciated. Here the error log: (I would post a picture but I don't have 10 rep yet)

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.onMeasure(android.support.v7.widget.RecyclerView$Recycler, android.support.v7.widget.RecyclerView$State, int, int)' on a null object reference
        at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
        at android.view.View.measure(View.java:17430)
        at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727)
        at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
        at android.view.View.measure(View.java:17430)
        at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:851)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
        at android.view.View.measure(View.java:17430)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5786)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

回答1:

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);

回答2:

In my case it was not connected to 'final', but to the issue mentioned in @NemanjaKovačević comment to @aga answer. I was setting a layoutManager on data load and that was the cause of the same crash. After moving the layoutManager setup to onCreateView of my fragment the issue was fixed.

Something like this:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
{
...
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recycler);

mLayoutManager = new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL);
mRecyclerView.setLayoutManager(mLayoutManager);

回答3:

For me, I was having the same issue, the issue was that there was an unused RecyclerView in xml with view gone but I am not binding it to any adapter in Activity, hence the issue. It was solved as soon as I removed such unused recycler views in xml

i.e - I removed this view as this was not called in code or any adapter has been set

<android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/rv_profileview_allactivities"
        android:visibility="gone" />

回答4:

I experienced this crash even though I had the RecyclerView.LayoutManager properly set. I had to move the RecyclerView initialization code into the onViewCreated(...) callback to fix this issue.

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_listing, container, false);
    rootView.setTag(TAG);
    return inflater.inflate(R.layout.fragment_listing, container, false);
}

@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    mLayoutManager = new LinearLayoutManager(getActivity());
    mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);

    mRecyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    mRecyclerView.setItemAnimator(new DefaultItemAnimator());
    mRecyclerView.setLayoutManager(mLayoutManager);

    mAdapter = new ListingAdapter(mListing);
    mRecyclerView.setAdapter(mAdapter);
}

回答5:

You need to use setLayoutManager in the RecyclerView#onCreate() method. Before adding recyclerView to a view, it must have the LayoutManager set.

 private RecyclerView menuAsList;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);

    menuAsList = (RecyclerView) findViewById(R.id.recyclerView_mainMenu);
    menuAsList.setLayoutManager(new LinearLayoutManager(Home.this));

}

回答6:

recyclerView =
            (RecyclerView) findViewById(R.id.recycler_view2);

Check with you recycler view ID, pointing to actual recycler view solved my issue

回答7:

I got this issue due to wrong reference of RecyclerView id.

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

to

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

回答8:

My problem was in my XML lyout I have an android:animateLayoutChanges set to true and I've called notifyDataSetChanged() on the RecyclerView's adapter in the Java code.

So, I've just removed android:animateLayoutChanges from my layout and that resloved my problem.

回答9:

Since LinearLayoutManager is vertical by default, an easier way to do this is:

recyclerView.setLayoutManager(new LinearLayoutManager(context));

If you want to change the orientation you could use this constructor:

public LinearLayoutManager(Context context, int orientation, boolean reverseLayout);

回答10:

I think the problem in your Adapter. Make sure you have returned ViewHolder in onCreateViewHolder(). Like below:

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

回答11:

I had this problem when using Butterknife library. I had:

View rootView = inflater.inflate
                (R.layout.fragment_recipe_detail_view, container, false);
ButterKnife.bind(rootView);

But the correct version is:

View rootView = inflater.inflate
                (R.layout.fragment_recipe_detail_view, container, false);
ButterKnife.bind(this, rootView);

回答12:

For me the problem was with my activity_main.xml(21) in which the recycleView didn't have an id.

activity_main.xml(21)

 <android.support.v7.widget.RecyclerView
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginRight="8dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/button3"
    tools:listitem="@layout/transaction_list_row" />

activity_main.xml

<android.support.v7.widget.RecyclerView

    android:id="@+id/transac_recycler_view"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginRight="8dp"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.0"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/button3"
    />

It worked when i added a android:id="@+id/transac_recycler_view" to the activity_main.xml(21) recycleView

回答13:

In Gradle implement this library :

implementation 'com.android.support:appcompat-v7:SDK_VER'
implementation 'com.android.support:design:SDK_VER'
implementation 'com.android.support:support-v4:SDK_VER'
implementation 'com.android.support:support-v13:SDK_VER'
implementation 'com.android.support:recyclerview-v7:SDK_VER'

In XML mention like this :

<android.support.v7.widget.RecyclerView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:id="@+id/recyclerView"/>

In Fragment we use recyclerView like this :

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
       View rootView = inflater.inflate(R.layout.YOUR_LAYOUT_NAME, container, false);

       RecyclerView recyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false);
        recyclerView.setLayoutManager(layoutManager);
        APICallMethod();
        YOURADAPTER = new YOURADAPTER(getActivity(), YOUR_LIST); // you can use that adapter after for loop in response(APICALLMETHOD)
        recyclerView.setAdapter(YOURADAPTER);
        return rootView;
    }

In Activity we use RecyclerView like this :

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.YOUR_LAYOUT_NAME);

        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false);
        recyclerView.setLayoutManager(layoutManager);
        APICallMethod();
        YOURADAPTER = new YOURADAPTER(ACTIVITY_NAME.this, YOUR_LIST); // you can use that adapter after for loop in response(APICALLMETHOD)
        recyclerView.setAdapter(YOURADAPTER);
   }

if you need horizontal RecyclerView do this :

RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
        recyclerView.setLayoutManager(layoutManager);
        APICallMethod();
        YOURADAPTER = new YOURADAPTER(ACTIVITY_NAME.this, YOUR_LIST); // you can use that adapter after for loop in response(APICALLMETHOD)
        recyclerView.setAdapter(YOURADAPTER);

if you want to use GridLayoutManager using RecyclerView use like this :

        RecyclerView recyclerView = findViewById(R.id.rvNumbers);
        recyclerView.setLayoutManager(new GridLayoutManager(this, 3)); // 3 is number of columns.
        adapter = new MyRecyclerViewAdapter(this, data);
        recyclerView.setAdapter(adapter);

回答14:

I was using a Dependency Injection - ButterKnife and this problem arised because I had not binded the view.

So inside onCreate() I just inserted this line:

ButterKnife.bind(this);

My RecyclerView declaration with Dependency Injection:

@BindView(R.id.recyclerview)
RecyclerView recyclerView;

回答15:

If I where you I will do this. onView(withId(android.R.id.list)).perform(RecyclerViewActions.scrollToPosition(3)); android.R.id.list change it to your list id and position will be your position inside your array.