带有自定义数组适配器的 Rss reader

Question

我在 android studio 中制作一个带有 rss feed 的 android 应用程序，所以我试图将标题和描述从：http://feeds.bbci.co.uk/news/rss.xml 放入两个文本视图使用自定义适配器。 rss 提要在选项卡中。每次我尝试运行我的程序时，我都会遇到异常，问题出现在 class:

    public class LAdapter extends ArrayAdapter<Info> {
    public LAdapter(Context context, ArrayList<Info> nfos) {super(context, 0,nfos);}

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // Get the data item for this position
        Info info = getItem(position);
        // Check if an existing view is being reused, otherwise inflate the view
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.basic_list_item, parent, false);
        }
        // Lookup view for data population
        TextView title = (TextView) convertView.findViewById(R.id.Tit);
        TextView description = (TextView) convertView.findViewById(R.id.Desc);

        title.setText(info.Title);
        description.setText(info.Description);

        // Return the completed view to render on screen
        return convertView;
    }
}

部分Tab_1.class:

public class Tab_1 extends Fragment {
ListView mList;
ArrayList<Info> arrayOfInfo;
LAdapter adapter;

@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);
    LAdapter adapter = new LAdapter(getActivity(), arrayOfInfo);
#Line 44->  mList = (ListView) v.findViewById(R.id.list);
    new GetRssFeed().execute("http://feeds.bbci.co.uk/news/rss.xml");
    mList.setAdapter(adapter);
    return v;
}

异常：

Process: com.example.pauly.myapplication, PID: 3896
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.onCreateView(Tab_1.java:43)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1789)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:955)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1138)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:740)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1501)
        at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:490)
        at 

android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1072)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:918)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1440)
...

Answer 1

LAdapter adapter = new LAdapter(getActivity(), arrayOfInfo);

arrayOfInfo 为空（甚至未初始化），因为您在 arrayOfInfo 之后调用了异步任务。使用从 DoInBackground 方法接收到的数据，您可以在 asynctask 的 OnPostExecute 方法中用数据设置 arrayOfInfo，在用数据设置该数组后，您也可以在 OnPostExecute 中调用

LAdapter adapter = new LAdapter(getActivity(), arrayOfInfo);
mList.setAdapter(adapter);

OnPostExecute 基本上是在处理您的 UI.

带有自定义数组适配器的 Rss reader

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