如何正确利用doinBackground（）方法以检索RSS项

问题描述

现在，我正在创建一个RSS阅读器，主要是试图使项目的标题和描述显示在ListView上。 我之前没有RSS数据对其进行过测试，并确认该应用正确列出了我创建的项目。 但是，在尝试对RSS中的数据进行相同处理后，我在检索实际RSS数据以及如何使用doinBackground方法时遇到了问题。

阅读Google关于doinBackground的文档后，我了解到它的类（Async）允许执行后台操作并将其结果显示在UI线程中。 但是，我通常在提取RSS数据以及doinBackground（）如何适合我的代码方面遇到问题。 关于如何正确检索数据并有效使用doinbackground（）的任何想法？

我遇到麻烦的代码类别是Headlines和RSSManager。 这是代码：

标题片段

import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import java.net.MalformedURLException;
import java.net.URL;

public class Headlines extends Fragment {
EditText editText;
Button gobutton;
ListView listView;

public Headlines() {
}

@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.fragment_headlines, container, false);
    editText = (EditText)v.findViewById(R.id.urlText);
    gobutton = (Button)v.findViewById(R.id.goButton);
    listView = (ListView)v.findViewById(R.id.listView);
    RSSFeedManager rfm = new RSSFeedManager();
    News [] news = new News[100]; // i shouldnt have to set the size of the array here since I did it in getFeed() in RSSFeedManager.java
    try {
        news = rfm.getFeed(String.valueOf(new URL("http://rss.cnn.com/rss/cnn_world.rss")));
    } catch (MalformedURLException e) {
        e.printStackTrace();
    }
    RssAdapter adapter = new RssAdapter(this.getActivity(),news);
    listView.setAdapter(adapter);
    /*gobutton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

        }
    });*/
    return v;
}

}

RSSFeedManager

import android.os.AsyncTask;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

public class RSSFeedManager extends AsyncTask<String,Void,String> {
public URL rssURL;
News[] articles;

public News[] getFeed(String url) {
    try {
        String strURL = url;
        rssURL = new URL(url);
        DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document doc = builder.parse(rssURL.openStream());

        //using Nodelist to get items within the rss, then creating
        //a News array the same size of the amount of items within the rss
        //then setting up a temporary "News" item which will be the temp object
        //used for storing multiple objects that contain title and description
        //of each item
        NodeList items = doc.getElementsByTagName("item");
        News[] articles = new News[items.getLength()];
        News news = null;

        //traverse through items and place the contents of each item within an RssItem object
        //then add to it to the News Array
        for (int i = 0; i < items.getLength(); i++) {
            Element item = (Element) items.item(i);
            news.setTitle(getValue(item, "title"));
            news.setDescription(getValue(item, "description"));
            articles[i] = news;
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return articles;
}

public String getValue(Element parent, String nodeName) {
    return parent.getElementsByTagName(nodeName).item(0).getFirstChild().getNodeValue();
}

@Override
protected String doInBackground(String... url) {
    String rssURL = url[0];
    URL urlTemp;
    try {
        //pulling the url from the params and converting it to type URL and then establishing a connection
        urlTemp = new URL(rssURL);
        HttpURLConnection urlConnection = (HttpURLConnection) urlTemp.openConnection();
        urlConnection.connect();
        /*
        *im thinking i need to call the getFeed() method
        *after establishing the httpurlconnection however
        *I also thought I may just need to move the getFeed()
        *code within doinBackground. Lost at this point due to the
        * return types of getFeed and doinBackground
        */
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

}