Question

我刚试过我目前正在处理的新闻应用程序的retrofit2，我试图在片段类中调用我的API实现。但我一直得到nullpointerexception，这是我的片段代码：

public class IgnFragment extends Fragment {


@BindView(R.id.ignNewsContainer)
RecyclerView ignNewsContainer;
Unbinder unbinder;

Call<NewsArticle> call;
public IgnFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_ign, container, false);
    unbinder = ButterKnife.bind(this, view);
    return view;

}

@Override
public void onStart() {
    super.onStart();
     call = NewsApi.getApi().getArticles("ign", "top");
    getClient();
}
public void getClient(){
    call.enqueue(new Callback<NewsArticle>() {
        @Override
        public void onResponse(Call<NewsArticle> call, Response<NewsArticle> response) {
            NewsArticle newsArticle = response.body();
            NewsAdapter newsAdapter = new NewsAdapter(newsArticle.getArticles(),getContext());
            ignNewsContainer.setAdapter(newsAdapter);
            LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getContext());
            linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
            ignNewsContainer.setLayoutManager(linearLayoutManager);
        }

        @Override
        public void onFailure(Call<NewsArticle> call, Throwable t) {
            t.printStackTrace();
            Log.e("Error","Called");
        }
    });
}

@Override
public void onDestroyView() {
    super.onDestroyView();
    unbinder.unbind();
}

这是我的api服务类：

public class NewsApi {
private static final String API_KEY = "________";
private static final String URL_BASE ="https://newsapi.org/v1/";


private static NewsService newsService =null;
public static NewsService getApi(){
   if(newsService == null){
       Retrofit retrofit= new Retrofit.Builder()
               .baseUrl(URL_BASE)
               .addConverterFactory(GsonConverterFactory.create())
               .client(getClient())
               .build();
        NewsService api = retrofit.create(NewsService.class);
   }
    return newsService;
}

public static OkHttpClient getClient(){
    HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
    logging.setLevel(HttpLoggingInterceptor.Level.BODY);
    OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
    return  httpClient.addInterceptor(logging).build();
}

public interface  NewsService{
    @GET("articles?apiKey=" + API_KEY)
    Call<NewsArticle> getArticles(@Query("source") String source,@Query("sortBy") String sortBy);
}

}

这是我得到的错误：

10-30 20：42：01.640 32640-32640 / cc.codemonkey.newsportal E / AndroidRuntime：致命异常：主要处理：cc.codemonkey.newsportal，PID：32640 java.lang.NullPointerException：尝试调用接口方法＆＃39; retrofit2.Call cc.codemonkey.newsportal.service.NewsApi $ NewsService.getArticles（java.lang.String，java.lang.String）＆＃39;在null对象引用上在cc.codemonkey.newsportal.fragments.IgnFragment.onStart（IgnFragment.java:54）在android.support.v4.app.Fragment.performStart（Fragment.java:2265）在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1369）在android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState（FragmentManager.java:1574）在android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1641）在android.support.v4.app.BackStackRecord.executeOps（BackStackRecord.java:794）在android.support.v4.app.FragmentManagerImpl.executeOps（FragmentManager.java:2415）在android.support.v4.app.FragmentManagerImpl.executeOpsTogether（FragmentManager.java:2200）在android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps（FragmentManager.java:2153）在android.support.v4.app.FragmentManagerImpl.execSingleAction（FragmentManager.java:2034）在android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss（BackStackRecord.java:651）在android.support.v4.app.FragmentPagerAdapter.finishUpdate（FragmentPagerAdapter.java:143）在android.support.v4.view.ViewPager.populate（ViewPager.java:1239）在android.support.v4.view.ViewPager.populate（ViewPager.java:1087）在android.support.v4.view.ViewPager.onMeasure（ViewPager.java:1613）在android.view.View.measure（View.java:17442）在android.widget.RelativeLayout.measureChildHorizontal（RelativeLayout.java:727）在android.widget.RelativeLayout.onMeasure（RelativeLayout.java:463）在android.view.View.measure（View.java:17442）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）在android.widget.FrameLayout.onMeasure（FrameLayout.java:430）在android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:139）在android.view.View.measure（View.java:17442）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1436）在android.widget.LinearLayout.measureVertical（LinearLayout.java:722）在android.widget.LinearLayout.onMeasure（LinearLayout.java:613）在android.view.View.measure（View.java:17442）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）在android.widget.FrameLayout.onMeasure（FrameLayout.java:430）在android.view.View.measure（View.java:17442）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1436）在android.widget.LinearLayout.measureVertical（LinearLayout.java:722）在android.widget.LinearLayout.onMeasure（LinearLayout.java:613）在android.view.View.measure（View.java:17442）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5463）在android.widget.FrameLayout.onMeasure（FrameLayout.java:430）在com.android.internal.policy.impl.PhoneWindow $ DecorView.onMeasure（PhoneWindow.java:2560）在android.view.View.measure（View.java:17442）在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2001）在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1166）在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1372）在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1054）在android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:5779）在android.view.Choreographer $ CallbackRecord.run（Choreographer.java:767）在android.view.Choreographer.doCallbacks（Choreographer.java:580）在android.view.Choreographer.doFrame（Choreographer.java:550）在android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:753）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:135）在android.app.ActivityThread.main（ActivityThread.java:5253）在java.lang。

Answer 1

你的问题就在这一行

NewsAdapter newsAdapter = new NewsAdapter(newsArticle.getArticles(),getContext());

问题是新闻文章正在null已经在这里初始化

NewsArticle newsArticle = response.body();

所以response.body()为空请尝试调试并查看为什么它是空的！解决这个问题时，你的解决方案应该可行并且alos引用此What is a NullPointerException, and how do I fix it?来了解更多NullPointerException。

Answer 2

如果您使用的是retrofit2，请检查您的“新闻”类是否正确写成

@SerializedName("articles")
@Expose
private List<Article> articles;

而不是

@SerializedName("article")  <------ article != articles
@Expose
private List<Article> articles;

尝试访问API

2 个答案: