Question

我为这个简单的问题而疯狂。实际上，我在其中传递了2个列表的适配器。

我的第二个List在适配器中始终为null，这就是为什么我每次都有NullPointException的原因。

所以...我不知道为什么


public class MyAdapter extends RecyclerView.Adapter<ViewHolder> {

    private List<Result> articles;
    private RequestManager glide;
    private List<Business.Response.Doc> doc;
    private Business.Response.Doc doc1;

    public MyAdapter(List<Result> articles, RequestManager glide, List<Business.Response.Doc> docs) {
        this.articles = articles;
        this.glide = glide;
        this.doc = docs;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // CREATE VIEW HOLDER AND INFLATING ITS XML LAYOUT
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.fragment_view_recycler, parent, false);

        return new ViewHolder(view);
    }


    // UPDATE VIEW HOLDER WITH ARTICLES
    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int position) {
        viewHolder.updateWithArticles(this.articles.get(position), glide, doc.get(position)); }

    // RETURN THE TOTAL COUNT OF ITEMS IN THE LIST
    @Override
    public int getItemCount() {
        return this.doc.size() + this.articles.size();

    }

    public Result getarticles(int position) {
        return this.articles.get(position);
    }

    public Business.Response.Doc getDocs(int position) {return this.doc.get(position);}
}

我的第一个列表，当我启动调试模式时，其大小为0。非常好。但是mySecond List为空。

我做错什么了吗？

这是我的CrashLog

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mynews, PID: 3154
    java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
        at com.example.mynews.MyAdapter.getItemCount(MyAdapter.java:47)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3834)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3639)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4194)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.swiperefreshlayout.widget.SwipeRefreshLayout.onLayout(SwipeRefreshLayout.java:625)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.viewpager.widget.ViewPager.onLayout(ViewPager.java:1775)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.appcompat.widget.LinearLayoutCompat.setChildFrame(LinearLayoutCompat.java:1645)
        at androidx.appcompat.widget.LinearLayoutCompat.layoutVertical(LinearLayoutCompat.java:1499)
        at androidx.appcompat.widget.LinearLayoutCompat.onLayout(LinearLayoutCompat.java:1407)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.drawerlayout.widget.DrawerLayout.onLayout(DrawerLayout.java:1231)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:753)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2792)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2319)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
        at android.view.Choreographer.doCallbacks(Choreographer.java:761)
        at android.view.Choreographer.doFrame(Choreographer.java:696)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)

Answer 1

只需在您访问的this.doc的每个位置添加一个空检查。如果为空，则列表将更短。

if (doc != null) {
    ...
}

我不知道同一视图应该如何显示Result和doc，所以我会创建两个不同的视图-每种类型一个。这就是参数viewType的作用。

如何在我的适配器中修复此NullPointerException？

1 个答案: