接口实例的空指针异常

Question

我正在做一个新闻app.But，当我在ListFragment中实现OnSendResultInterface时遇到空指针异常.Below是我的List片段。方法是sendResult。

    public class ListFragment extends Fragment implements OnItemClickListener,
    OnSendResultInterface {
private ListView mListview;
private OnItemPressListener mItempressed;

@Override
public void onAttach(Activity activity) {
    .......
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    ..........
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
        long id) {
    if (null != mItempressed) {
        mItempressed.OnItemPress(position);
    }
}

@Override
public void sendResult(List<Entry> result) {
Log.v("result", "result" + result);
    RssAdapter adapter = new RssAdapter(getActivity(), result);
    mListview.setAdapter(adapter);
}
}

这是我的DownloadXmlTask​​.In这个类我初始化界面并声明方法。

    public class DownloadXmlTask extends AsyncTask<String, Void, List<Entry>> {
private OnSendResultInterface mSendResult;<---this is the listener

@Override
protected List<Entry> doInBackground(String... urls) {
.......
}

@Override
protected void onPostExecute(List<Entry> result) {
    if (null != result)
        mSendResult.sendResult(result);  <----null pointer exception shown here.

}

public List<Entry> downloadUrl(String urlString) throws IOException {
    ..........
}
}

Answer 1

mSendResult变量未在任何地方初始化。