Question

我有一个加载在Tab上的片段，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。

顶部有一张卡，其余数据有多张卡。它的表示如下：

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：

应用程序意外停止：线程[main，5，main]失败： java.lang.NullPointerException：尝试调用虚方法＆＃39;布尔 android.support.v7.widget.RecyclerView $ LayoutManager.canScrollHorizontally（）＆＃39; 在null对象引用 android.support.v7.widget.RecyclerView.computeHorizontalScrollOffset（RecyclerView.java:1548）在android.view.View.canScrollHorizontally（View.java:12827）at android.support.v4.view.ViewCompatICS.canScrollHorizontally（ViewCompatICS.java:31）在 android.support.v4.view.ViewCompat $ ICSViewCompatImpl.canScrollHorizontally（ViewCompat.java:1249）在 android.support.v4.view.ViewCompat.canScrollHorizontally（ViewCompat.java:1684）在android.support.v4.view.ViewPager.canScroll（ViewPager.java:2561）在android.support.v4.view.ViewPager.canScroll（ViewPager.java:2552）在android.support.v4.view.ViewPager.canScroll（ViewPager.java:2552）在 android.support.v4.view.ViewPager.onInterceptTouchEvent（ViewPager.java:1923）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:1961）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at android.view.ViewGroup.dispatchTransformedTouchEvent（ViewGroup.java:2406）在android.view.ViewGroup.dispatchTouchEvent（ViewGroup.java:2107）at com.android.internal.policy.impl.PhoneWindow $ DecorView.superDispatchTouchEvent（PhoneWindow.java:2625）在 com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent（PhoneWindow.java:1770）在android.app.Activity.dispatchTouchEvent（Activity.java:2742）处 android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent（WindowCallbackWrapper.java:60）在 android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent（WindowCallbackWrapper.java:60）在 com.android.internal.policy.impl.PhoneWindow $ DecorView.dispatchTouchEvent（PhoneWindow.java:2586）在android.view.View.dispatchPointerEvent（View.java:8675）处 android.view.ViewRootImpl $ ViewPostImeInputStage.processPointerEvent（ViewRootImpl.java:4129）在 android.view.ViewRootImpl $ ViewPostImeInputStage.onProcess（ViewRootImpl.java:3995）在 android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3550）在 android.view.ViewRootImpl $ InputStage.onDeliverToNext（ViewRootImpl.java:3603）在 android.view.ViewRootImpl $ InputStage.forward（ViewRootImpl.java:3569）在 android.view.ViewRootImpl $ AsyncInputStage.forward（ViewRootImpl.java:3686）在android.view.ViewRootImpl $ InputStage.apply（ViewRootImpl.java:3577）在 android.view.ViewRootImpl $ AsyncInputStage.apply（ViewRootImpl.java:3743）在 android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3550）在 android.view.ViewRootImpl $ InputStage.onDeliverToNext（ViewRootImpl.java:3603）在 android.view.ViewRootImpl $ InputStage.forward（ViewRootImpl.java:3569）在android.view.ViewRootImpl $ InputStage.apply（ViewRootImpl.java:3577）在 android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3550）在 android.view.ViewRootImpl.deliverInputEvent（ViewRootImpl.java:5813）在 android.view.ViewRootImpl.doProcessInputEvents（ViewRootImpl.java:5787）在 android.view.ViewRootImpl.enqueueInputEvent（ViewRootImpl.java:5758）在 android.view.ViewRootImpl $ WindowInputEventReceiver.onInputEvent（ViewRootImpl.java:5903）在 android.view.InputEventReceiver.dispatchInputEvent（InputEventReceiver.java:185）在 android.view.InputEventReceiver.nativeConsumeBatchedInputEvents（母语方法）at android.view.InputEventReceiver.consumeBatchedInputEvents（InputEventReceiver.java:176）在 android.view.ViewRootImpl.doConsumeBatchedInput（ViewRootImpl.java:5874）在 android.view.ViewRootImpl $ ConsumeBatchedInputRunnable.run（ViewRootImpl.java:5926）在 android.view.Choreographer $ CallbackRecord.run（Choreographer.java:767）在android.view.Choreographer.doCallbacks（Choreographer.java:580）at android.view.Choreographer.doFrame（Choreographer.java:548）at android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:753）在android.os.Handler.handleCallback（Handler.java:739）处 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）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:699）

我想问的第二件事是你是否认为这是实现这一目标的正确方法。我应该在RecyclerView中使用多个视图持有者吗？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主题并尝试了很多不同的组合，但似乎无法解决这个问题。

任何帮助都非常感激。

由于

Answer 1

因此，您的层次结构中的某个地方似乎没有设置RecyclerView的额外LayoutManager。

如果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NullPointerException实例上调用canScrollHorizontally()时由RecyclerView$LayoutManager导致崩溃。

在片段

1 个答案: