Rss Feeds reader gives blank screen for .xml link

问题

I am following this tutorial (http://techiedreams.com/android-rss-reader-part-two-offline-reading-swipe-through-detail-views/)and try to implement rss feed reader

It working properly when I use

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

instead of using

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

This is my splash activity

 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;
    }
}

Here is my 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;
    }

}

Below part of the above code gives null pointer exception

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*/

This is my 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;
    }
}

Simply what the above code does is

DOM Parser to Parse the XML data. method returns the feed(RSSFeed) object:

Splash Activity we now call the method parseXml(String xml) from the DOMParser class

feed has been obtained in the onPostExecute() method we need to start the ListActivity and pass it the feed we got, we do that by bundling the feed object and attaching it to the Intent

来源：https://stackoverflow.com/questions/30000340/rss-feeds-reader-gives-blank-screen-for-xml-link