列表返回 null

Question

我正在制作一个带有标签的 android studio 应用程序，其中一个标签有一个 rss 提要，我试图将来自http://feeds.bbci.co.uk/news/rss.xml 的帖子的标题和描述放入列表视图，但我得到一个例外：

    java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
        at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
        at android.widget.ListView.setAdapter(ListView.java:487)
        at com.example.pauly.myapplication.Tabs.Tab_1$GetRssFeed.onPostExecute(Tab_1.java:65)
        at com.example.pauly.myapplication.Tabs.Tab_1$GetRssFeed.onPostExecute(Tab_1.java:45)
        at android.os.AsyncTask.finish(AsyncTask.java:636)
        at android.os.AsyncTask.access$500(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        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:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Tab_1.java：

public class Tab_1 extends Fragment {
    ListView mList;
    ArrayList<Info> arrayOfInfo;
    int i=0;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.tab_1, container, false);
        mList = (ListView) v.findViewById(R.id.list);
        new GetRssFeed().execute("http://feeds.bbci.co.uk/news/rss.xml");

        return v;
    }

   l.45- private class GetRssFeed extends AsyncTask<String, Void, Void> {
        @Override
        protected Void doInBackground(String... params) {
            try {
                RssReader rssReader = new RssReader(params[0]);
                for (RssItem item : rssReader.getItems()) {
                    arrayOfInfo.add(i++, new Info(item.getTitle(), item.getDescription()));
                }
            } catch (Exception e) {
                Log.v("Error Parsing Data", e + "");
            }
            return null;
        }


        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            LAdapter adapter = new LAdapter(getActivity(), arrayOfInfo);
            adapter.notifyDataSetChanged();
       l.65 mList.setAdapter(adapter);
        }
    }
}

Answer 1

您需要分配 ArrayList 对象；

ArrayList<Info> arrayOfInfo;

替换为

ArrayList<Info> arrayOfInfo=new ArrayList<>();