Java 试图从自定义适配器调用onClick方法时出现空指针异常

我试图在Android Studio中编写自己的适配器类，它看起来像这样：

public class Adapter extends RecyclerView.Adapter<Adapter.MyViewHolder>{

    private List<Article> articles;
    private Context context;
    private OnItemClickListener onItemClickListener;


    public Adapter(List<Article> articles, Context context) {
        this.articles = articles;
        this.context = context;
    }

    public void setOnItemClickListener(OnItemClickListener onItemClickListener){
        this.onItemClickListener = onItemClickListener;
    }

    public interface OnItemClickListener {
        void onItemClick(View view, int position);
    }

    public class MyViewHolder extends RecyclerView.ViewHolder implements  View.OnClickListener {

        TextView title, desc, author, published_ad, source, time;
        ImageView imageView;
        ProgressBar progressBar;
        OnItemClickListener onItemClickListener;

        public MyViewHolder(View itemView, OnItemClickListener onItemClickListener) {

            super(itemView);

            itemView.setOnClickListener(this);
            title = itemView.findViewById(R.id.title);
            desc = itemView.findViewById(R.id.decs);
            author = itemView.findViewById(R.id.author);
            published_ad = itemView.findViewById(R.id.publishedAt);
            source = itemView.findViewById(R.id.source);
            time = itemView.findViewById(R.id.time);
            imageView = itemView.findViewById(R.id.img);
            progressBar = itemView.findViewById(R.id.progress_load_photo);

            this.onItemClickListener = onItemClickListener;

        }

        @Override
        public void onClick(View v) {
            onItemClickListener.onItemClick(v, getAdapterPosition());
        }
    }
}

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

        recyclerView = view.findViewById(R.id.recyclerView);
        layoutManager = new LinearLayoutManager(getContext());
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setNestedScrollingEnabled(false);

        adapter = new Adapter(articles, getActivity().getApplicationContext());
        recyclerView.setAdapter(adapter);
        LoadJson();

        return view;
    }

---

我得到了一个关于空指针异常的错误：“在空对象引用上尝试调用接口方法'void com.example.app2.Adapter$OnItemClickListener.onItemClick（android.view.view，int）'”

您的字段

Adapter.OnItemClickListener

在您设置它之前是空的（您在实际代码中从来没有这样做过）

因此，在尝试通知它之前，您应该测试是否存在侦听器

@覆盖
公共void onClick（视图v）{
如果（MClickListener！=null）
onItemClickListener.onItemClick（v，getAdapterPosition（））；
}

我猜您会在

onCreateView

方法中使用它：）

adapter=新适配器（articles，getActivity（）.getApplicationContext（））；
setOnItemClickListener（（）->{System.out.println（“Click！”）}）；
recyclerView.setAdapter（适配器）；

您忘记在

适配器上设置
侦听器
。您可以在执行
RecyclerView
和
Adapter
设置的其余部分时设置它。