空对象引用上的错误“ java.lang.Class java.lang.Object.getClass（）”

Question

  

嗨，我正在开发android，但启动后却遇到了以下异常   ava.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'java.lang.Class java.lang.Object.getClass（）'           在edgar.yodgorbek.sportnews.sportactivities.BBCSportFragment $ 1.onResponse（BBCSportFragment.java:69）

在BBCSportFragment类之下

public class BBCSportFragment extends Fragment implements ArticleAdapter.ClickListener {

    public List<Article> articleList = new ArrayList<>();
    @ActivityContext
    public Context activityContext;
    @ApplicationContext
    public Context mContext;

    @BindView(R.id.recycler_view)
    RecyclerView recyclerView;
    BBCSportFragmentComponent bbcSportFragmentComponent;
    BBCFragmentContextModule bbcFragmentContextModule;
    private SportNews sportNews;
    private ArticleAdapter articleAdapter;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_bbcsport, container, false);
        ButterKnife.bind(this, view);
        SportInterface sportInterface = SportClient.getApiService();
        Call<SportNews> call = sportInterface.getArticles();
        call.enqueue(new Callback<SportNews>() {
            @Override
            public void onResponse(Call<SportNews> call, Response<SportNews> response) {
                sportNews = response.body();
                if (sportNews != null && sportNews.getArticles() != null) {
                    articleList.addAll(sportNews.getArticles());
                }
                articleAdapter = new ArticleAdapter(articleList, sportNews);
                ApplicationComponent applicationComponent = MyApplication.get((Activity) getContext()).getApplicationComponent();
                bbcSportFragmentComponent = (BBCSportFragmentComponent) DaggerApplicationComponent.builder().contextModule(new ContextModule(getContext())).build();
                bbcSportFragmentComponent.injectBBCSportFragment(BBCSportFragment.this);
                RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getContext());
                recyclerView.setLayoutManager(layoutManager);
                recyclerView.setAdapter(articleAdapter);
            }

            @Override
            public void onFailure(Call<SportNews> call, Throwable t) {

            }
        });
        return view;
    }
}

  

ArticleAdapter下面

public class ArticleAdapter extends RecyclerView.Adapter<ArticleAdapter.CustomViewHolder> {

    public static final String urlKey = "urlKey";
    public static final String imageKey = "imageKey";
    public ArticleAdapter.ClickListener listener;
    Context context;
    private List<Article> articles = new ArrayList<Article>();

    public ArticleAdapter(List<Article> articles, SportNews sportNews) {
        this.articles = articles;
        this.listener = listener;

    }

    public ArticleAdapter(ArticleAdapter.ClickListener clickListener) {
    }

    @NonNull
    @Override
    public CustomViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View itemView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.article_list, null);
        return new CustomViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull CustomViewHolder customViewHolder, int position) {
        Article article = articles.get(position);
        customViewHolder.articleAuthor.setText(article.getAuthor());
        customViewHolder.articleTitle.setText(article.getTitle());
        Picasso.get().load(article.getUrlToImage()).into(customViewHolder.articleImage);
        customViewHolder.itemView.setOnClickListener(v -> {
            Intent intent = new Intent(v.getContext(), DetailActivity.class);

            intent.putExtra("urlKey", article.getUrl());
            intent.putExtra("imageKey", article.getUrlToImage());

            v.getContext().startActivity(intent);
        });
    }


    @Override
    public int getItemCount() {
        if (articles == null) return 0;
        return articles.size();
    }

    public interface ClickListener {
    }

    public class CustomViewHolder extends RecyclerView.ViewHolder {
        @BindView(R.id.articleAuthor)
        TextView articleAuthor;
        @BindView(R.id.articleTitle)
        TextView articleTitle;
        @BindView(R.id.articleImage)
        ImageView articleImage;

        public CustomViewHolder(View view) {
            super(view);
            ButterKnife.bind(this, view);
        }
    }
}

Answer 1

以这种方式分配之前先进行空检查：

    @Override
            public void onResponse(Call<SportNews> call, Response<SportNews> response) {                   
                if(response!=null){
                sportNews = response.body();
                if (sportNews != null && sportNews.getArticles() != null) {
                    articleList.addAll(sportNews.getArticles());
                }
                articleAdapter = new ArticleAdapter(articleList, sportNews);
                ApplicationComponent applicationComponent = MyApplication.get((Activity) getContext()).getApplicationComponent();
                bbcSportFragmentComponent = (BBCSportFragmentComponent) DaggerApplicationComponent.builder().contextModule(new ContextModule(getContext())).build();
                bbcSportFragmentComponent.injectBBCSportFragment(BBCSportFragment.this);
                RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getContext());
                recyclerView.setLayoutManager(layoutManager);
                recyclerView.setAdapter(articleAdapter);
            }}

类似地，在从对象获取任何内容之前，请检查null以免出现nullpointer异常。

@Override
public void onBindViewHolder(@NonNull CustomViewHolder customViewHolder, int position) {
    Article article = articles.get(position);
     if(article!=null){
    customViewHolder.articleAuthor.setText(article.getAuthor());
    customViewHolder.articleTitle.setText(article.getTitle());
    Picasso.get().load(article.getUrlToImage()).into(customViewHolder.articleImage);}
    customViewHolder.itemView.setOnClickListener(v -> {
        Intent intent = new Intent(v.getContext(), DetailActivity.class);

        intent.putExtra("urlKey", article.getUrl());
        intent.putExtra("imageKey", article.getUrlToImage());

        v.getContext().startActivity(intent);
    });


}