android - 在 fragment 内滚动时出现 RecyclerView 错误

Question

我有一个加载到 Tab 上的 fragment ，然后加载 RecyclerView 并设置一个带有两个 ViewHolder 的适配器。屏幕上的数据通过CardViews显示在屏幕上。

一张卡片用于顶部数据，多张卡片用于其余数据。其表示如下:

我的第一个也是最大的问题是它可以正常加载，如上图所示，但是当我尝试滚动时出现错误:

Application has stopped unexpectedly: Thread[main,5,main] failed: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()' on a null object reference at android.support.v7.widget.RecyclerView.computeHorizontalScrollOffset(RecyclerView.java:1548) at android.view.View.canScrollHorizontally(View.java:12827) at android.support.v4.view.ViewCompatICS.canScrollHorizontally(ViewCompatICS.java:31) at android.support.v4.view.ViewCompat$ICSViewCompatImpl.canScrollHorizontally(ViewCompat.java:1249) at android.support.v4.view.ViewCompat.canScrollHorizontally(ViewCompat.java:1684) at android.support.v4.view.ViewPager.canScroll(ViewPager.java:2561) at android.support.v4.view.ViewPager.canScroll(ViewPager.java:2552) at android.support.v4.view.ViewPager.canScroll(ViewPager.java:2552) at android.support.v4.view.ViewPager.onInterceptTouchEvent(ViewPager.java:1923) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1961) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2406) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2107) at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2625) at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1770) at android.app.Activity.dispatchTouchEvent(Activity.java:2742) at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2586) at android.view.View.dispatchPointerEvent(View.java:8675) at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4129) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3995) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3550) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3603) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3569) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3686) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3577) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3743) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3550) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3603) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3569) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3577) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3550) at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5813) at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5787) at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5758) at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5903) at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) at android.view.InputEventReceiver.nativeConsumeBatchedInputEvents(Native Method) at android.view.InputEventReceiver.consumeBatchedInputEvents(InputEventReceiver.java:176) at android.view.ViewRootImpl.doConsumeBatchedInput(ViewRootImpl.java:5874) at android.view.ViewRootImpl$ConsumeBatchedInputRunnable.run(ViewRootImpl.java:5926) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) at android.view.Choreographer.doCallbacks(Choreographer.java:580) at android.view.Choreographer.doFrame(Choreographer.java:548) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5294) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)

我想问的第二件事是您认为这是否是实现它的正确方法。我应该在 RecyclerView 中使用多个 View 持有者吗？这会影响性能吗？

我的代码如下:

HomeFragment.java

public class HomeFragment extends Fragment{
    private List<Favourite> favourites;
    private RecyclerView rv;
    FavouriteAdapter fa;

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

        // Get recycler view reference
        rv = (RecyclerView) view.findViewById(R.id.favourite_card_rv);

        // Set layout manager
        rv.setLayoutManager(new LinearLayoutManager(getActivity()));

        // some data
        // This only returns a list of objects with some data
        initializeData();

        // Create adapter
        fa = new FavouriteAdapter(getActivity(), favourites);

        // Set adapter
        rv.setAdapter(fa);


        // return
        return view;
    }

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

FavouriteAdapter.java

public class FavouriteAdapter extends RecyclerView.Adapter<FavouriteAdapter.MainViewHolder> {

    List<Favourite> favourites;
    Context context;
    final int VIEW_TYPE_TOP = 0;
    final int VIEW_TYPE_FAVOURITES = 1;

    // Constructor
    public FavouriteAdapter(Context context, List<Favourite> favourites) {
        if (favourites == null) {
            throw new IllegalArgumentException(
                    "favourites must not be null");
        }
        this.favourites = favourites;
        this.context = context;
    }

    static class MainViewHolder extends  RecyclerView.ViewHolder {
        CardView cv;
        TextView videoName;
        TextView videoUrl;
        ImageView videoImage;

        public MainViewHolder(View v) {
            super(v);

            cv = (CardView)itemView.findViewById(R.id.cv);
            videoName = (TextView)itemView.findViewById(R.id.video_name);
            videoUrl = (TextView)itemView.findViewById(R.id.video_url);
            videoImage = (ImageView)itemView.findViewById(R.id.video_photo);
        }
    }

    static class TopFavouriteViewHolder extends MainViewHolder{
        TopFavouriteViewHolder(View itemView) {
            super(itemView);
        }
    }

    static class FavouriteViewHolder extends MainViewHolder {
        FavouriteViewHolder(View itemView) {
            super(itemView);
        }
    }


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

    @Override
    public int getItemViewType(int position) {
        return (position == 0? VIEW_TYPE_TOP : VIEW_TYPE_FAVOURITES);
    }

    @Override
    public MainViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
        View view;
        switch(viewType){
            case 0:
                view = LayoutInflater
                        .from(viewGroup.getContext())
                        .inflate(R.layout.top_card, viewGroup, false);
                return new TopFavouriteViewHolder(view);
            case 1:
                view = LayoutInflater
                        .from(viewGroup.getContext())
                        .inflate(R.layout.favourite_card, viewGroup, false);
                return new FavouriteViewHolder(view);
        }
        return null;
    }

    @Override
    public void onBindViewHolder(MainViewHolder holder, int i) {
        holder.videoName.setText(favourites.get(i).name);
        holder.videoUrl.setText(favourites.get(i).url);
        Picasso.with(this.context).load(favourites.get(i).image).into(holder.videoImage);
    }

    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
    }
}

我在这里查看了很多线程并尝试了很多不同的组合，但似乎无法解决这个问题。

非常感谢任何帮助。

谢谢

Answer 1

因此看起来您在层次结构中的某处有一个额外的 RecyclerView，但没有在其上设置 LayoutManager。

如果您查看堆栈跟踪的顶部:

Application has stopped unexpectedly: Thread[main,5,main] failed: 
    java.lang.NullPointerException: Attempt to invoke virtual method 
    'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollHorizontally()' 
    on a null object reference 
at android.support.v7.widget.RecyclerView.computeHorizontalScrollOffset(RecyclerView.java:1548) 

它表示在 RecyclerView$LayoutManager 实例上调用 canScrollHorizo​​ntally() 时由于 NullPointerException 而崩溃。