AsyncTask中的NullPointerException，其中检查值

Question

我正在Google Play中开发应用。 我的应用有＃34; Google Analytics＆＃34;我在例外中看到：

NullPointerException（@AsyncDownload：onPostExecute：70）

问题出在哪里？

public class AsyncDownload extends AsyncTask<String, Void, Feed > {

private FragmentCallback mFragmentCallback;

public AsyncDownload(FragmentCallback fragmentCallback) {
    mFragmentCallback = fragmentCallback;
}


@Override
protected void onPreExecute() {
    super.onPreExecute();
}

@Override
protected Void doInBackground(String... arg0) { 
    Feed feed = ArticlesManager.getInstance().getFeed(arg0[0]);

    if(feed==null){
        try {
                HttpGet get = new HttpGet(Ipsum.Headlines[Integer.valueOf(arg0[0])][2]);

                HttpParams httpParameters = new BasicHttpParams();
                HttpConnectionParams.setConnectionTimeout(httpParameters, 3000);
                HttpConnectionParams.setSoTimeout(httpParameters, 5000);

                HttpClient hc = new DefaultHttpClient();

                HttpResponse rp = hc.execute(get);
                if (rp.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
                    String res = EntityUtils.toString(rp.getEntity(),HTTP.UTF_8);

                    Feed feed = RssReader.read(res,Integer.valueOf(arg0[0]) == 7);
                    ArticlesManager.getInstance().addFeed(arg0[0], feed);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }    
    }

    return null;
}


protected void onPostExecute(final Feed feed){
    if(mFragmentCallback != null) {
        mFragmentCallback.onTaskDone(feed);
    }
}

}

Answer 1

请以这种方式更新 onPostExecute 方法并再次测试

protected void onPostExecute(final Feed feed)
{
    if(mFragmentCallback != null && feed != null) 
    {
        mFragmentCallback.onTaskDone(feed);
    }
    else
    {
       //the value is null
    }
}