Rss Feeds阅读器为.xml链接提供空白屏幕

Question

我正在关注本教程（http://techiedreams.com/android-rss-reader-part-two-offline-reading-swipe-through-detail-views/)and尝试实现rss提要阅读器

我使用

时工作正常

String RSSFEEDURL = "http://feeds.feedburner.com/androidcentral?format=xml";

而不是使用

String RSSFEEDURL = "http://www.livescience.com/home/feed/health.xml";

这是我的启动活动

 package com.healthyhub.nadeesha.rsssave;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Toast;

import com.healthyhub.nadeesha.rsssave.parser.DOMParser;
import com.healthyhub.nadeesha.rsssave.parser.RSSFeed;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class SplashActivity extends Activity {

     String RSSFEEDURL = "http://www.livescience.com/home/feed/health.xml";
   // String RSSFEEDURL = "http://feeds.feedburner.com/androidcentral?format=xml";





    RSSFeed feed;
    String fileName;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.splash);

        fileName = "TDRSSFeed.td";

        File feedFile = getBaseContext().getFileStreamPath(fileName);

        ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        if (conMgr.getActiveNetworkInfo() == null) {

// No connectivity. Check if feed File exists
            if (!feedFile.exists()) {

// No connectivity & Feed file doesn't exist: Show alert to exit
// & check for connectivity
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setMessage(
                        "Unable to reach server, \nPlease check your connectivity.")
                        .setTitle("TD RSS Reader")
                        .setCancelable(false)
                        .setPositiveButton("Exit",
                                new DialogInterface.OnClickListener() {
                                    @Override
                                    public void onClick(DialogInterface dialog,
                                                        int id) {
                                        finish();
                                    }
                                });

                AlertDialog alert = builder.create();
                alert.show();
            } else {

// No connectivty and file exists: Read feed from the File
                Toast toast = Toast.makeText(this,
                        "No connectivity! Reading last update...",
                        Toast.LENGTH_LONG);
                toast.show();
                feed = ReadFeed(fileName);
                startLisActivity(feed);
            }

        } else {

// Connected - Start parsing
            new AsyncLoadXMLFeed().execute();

        }
    }

    private void startLisActivity(RSSFeed feed) {

        Bundle bundle = new Bundle();
        bundle.putSerializable("feed", feed);

// launch List activity
        Intent intent = new Intent(SplashActivity.this, ListActivity.class);
        intent.putExtras(bundle);
        startActivity(intent);

// kill this activity
        finish();
    }

    private class AsyncLoadXMLFeed extends AsyncTask<Void, Void, Void> {

        @Override
        protected Void doInBackground(Void... params) {

// Obtain feed
            DOMParser myParser = new DOMParser();
            feed = myParser.parseXml(RSSFEEDURL);
            if (feed != null && feed.getItemCount() > 0)
                WriteFeed(feed);
            return null;

        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);

            startLisActivity(feed);
        }
    }

    // Method to write the feed to the File
    private void WriteFeed(RSSFeed data) {

        FileOutputStream fOut = null;
        ObjectOutputStream osw = null;

        try {
            fOut = openFileOutput(fileName, MODE_PRIVATE);
            osw = new ObjectOutputStream(fOut);
            osw.writeObject(data);
            osw.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                fOut.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    // Method to read the feed from the File
    private RSSFeed ReadFeed(String fName) {

        FileInputStream fIn = null;
        ObjectInputStream isr = null;

        RSSFeed _feed = null;
        File feedFile = getBaseContext().getFileStreamPath(fileName);
        if (!feedFile.exists())
            return null;

        try {
            fIn = openFileInput(fName);
            isr = new ObjectInputStream(fIn);

            _feed = (RSSFeed) isr.readObject();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                fIn.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return _feed;
    }
}

这是我的DOMParser.java

    package com.healthyhub.nadeesha.rsssave.parser;

import java.net.MalformedURLException;
import java.net.URL;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.jsoup.Jsoup;
import org.jsoup.select.Elements;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

public class DOMParser {

    private RSSFeed _feed = new RSSFeed();

    public RSSFeed parseXml(String xml) {

        // _feed.clearList();

        URL url = null;
        try {
            url = new URL(xml);
        } catch (MalformedURLException e1) {
            e1.printStackTrace();
        }

        try {
            // Create required instances
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();

            // Parse the xml
            Document doc = db.parse(new InputSource(url.openStream()));
            doc.getDocumentElement().normalize();

            // Get all <item> tags.
            NodeList nl = doc.getElementsByTagName("item");
            int length = nl.getLength();

            for (int i = 0; i < length; i++) {
                Node currentNode = nl.item(i);
                RSSItem _item = new RSSItem();

                NodeList nchild = currentNode.getChildNodes();
                int clength = nchild.getLength();

                // Get the required elements from each Item
                for (int j = 0; j < clength; j = j + 1) {

                    Node thisNode = nchild.item(j);
                    String theString = null;
                    String nodeName = thisNode.getNodeName();

                    /*newly added*/
                    /*here it returns NullPointer exception for theString*/
                    System.out.println( nchild.item(j).getFirstChild().getNodeValue());
                    /*end*/

                    theString = nchild.item(j).getFirstChild().getNodeValue();

                    if (theString != null) {
                        if ("title".equals(nodeName)) {
                            // Node name is equals to 'title' so set the Node
                            // value to the Title in the RSSItem.
                            _item.setTitle(theString);
                        } else if ("description".equals(nodeName)) {
                            _item.setDescription(theString);

                            // Parse the html description to get the image url
                            String html = theString;
                            org.jsoup.nodes.Document docHtml = Jsoup
                                    .parse(html);
                            Elements imgEle = docHtml.select("img");
                            _item.setImage(imgEle.attr("src"));
                        } else if ("pubDate".equals(nodeName)) {

                            // We replace the plus and zero's in the date with
                            // empty string
                            String formatedDate = theString.replace(" +0000",
                                    "");
                            _item.setDate(formatedDate);
                        }

                    }
                }

                // add item to the list
                _feed.addItem(_item);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        // Return the final feed once all the Items are added to the RSSFeed
        // Object(_feed).
        return _feed;
    }

}

以上部分代码给出了空指针异常

for (int j = 0; j < clength; j = j + 1) {

                    Node thisNode = nchild.item(j);
                    String theString = null;
                    String nodeName = thisNode.getNodeName();

                    /*newly added*/
                    /*here it returns NullPointer exception for theString*/
                    System.out.println( nchild.item(j).getFirstChild().getNodeValue());
                    /*end*/

这是我的DetailFragment.java

package com.healthyhub.nadeesha.rsssave;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.Display;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.webkit.WebSettings;
import android.webkit.WebSettings.LayoutAlgorithm;
import android.webkit.WebSettings.PluginState;
import android.webkit.WebView;
import android.widget.ScrollView;
import android.widget.TextView;

import com.healthyhub.nadeesha.rsssave.parser.RSSFeed;

public class DetailFragment extends Fragment {
    private int fPos;
    RSSFeed fFeed;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        fFeed = (RSSFeed) getArguments().getSerializable("feed");
        fPos = getArguments().getInt("pos");
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater
                .inflate(R.layout.detail_fragment, container, false);

// Initializr views
        TextView title = (TextView) view.findViewById(R.id.title);
        WebView desc = (WebView) view.findViewById(R.id.desc);

// Enable the vertical fading edge (by default it is disabled)
        ScrollView sv = (ScrollView) view.findViewById(R.id.sv);
        sv.setVerticalFadingEdgeEnabled(true);

// Set webview properties
        WebSettings ws = desc.getSettings();
        ws.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN);
        ws.setLightTouchEnabled(false);
        ws.setPluginState(PluginState.ON);
        ws.setJavaScriptEnabled(true);

// Set the views
        title.setText(fFeed.getItem(fPos).getTitle());
        desc.loadDataWithBaseURL("http://www.livescience.com/health/", fFeed
                .getItem(fPos).getDescription(), "text/html", "UTF-8", null);

        return view;
    }
}

以上代码的作用是

DOM解析器解析XML数据。  方法返回feed（RSSFeed）对象：

Splash Activity我们现在从DOMParser类调用方法parseXml（String xml）

已经在onPostExecute（）方法中获取了

feed我们需要启动ListActivity并将它传递给我们  得到了，我们通过捆绑feed对象并将其附加到Intent

来实现