How to wrap these classes into a AsyncClass and then using them?

Question

I'm trying to put together a simple RSS reader, and found code on http://www.ibm.com/developerworks/opensource/library/x-android/

Todo so, I noticed that you can not do network operations from the main thread since Honeycomb and have a hard time wrapping this class into a working AsyncTask:

package tlib.net.rss;

import java.util.ArrayList;
import java.util.List;

import android.sax.Element;
import android.sax.EndElementListener;
import android.sax.EndTextElementListener;
import android.sax.RootElement;
import android.util.Xml;

public class SaxFeedParser extends BaseFeedParser {

    public SaxFeedParser(String feedUrl) {
        super(feedUrl);
    }

    public List<Message> parse() {
        final Message currentMessage = new Message();
        RootElement root = new RootElement("rss");
        final List<Message> messages = new ArrayList<Message>();
        Element channel = root.getChild("channel");
        Element item = channel.getChild(ITEM);
        item.setEndElementListener(new EndElementListener(){
            public void end() {
                messages.add(currentMessage.copy());
            }
        });
        item.getChild(TITLE).setEndTextElementListener(new EndTextElementListener(){
            public void end(String body) {
                currentMessage.setTitle(body);
            }
        });
        item.getChild(LINK).setEndTextElementListener(new EndTextElementListener(){
            public void end(String body) {
                currentMessage.setLink(body);
            }
        });
        item.getChild(DESCRIPTION).setEndTextElementListener(new 
EndTextElementListener(){
            public void end(String body) {
                currentMessage.setDescription(body);
            }
        });
        item.getChild(PUB_DATE).setEndTextElementListener(new EndTextElementListener(){
            public void end(String body) {
                currentMessage.setDate(body);
            }
        });
        try {
            Xml.parse(this.getInputStream(), Xml.Encoding.UTF_8, root.getContentHandler());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        return messages;
    }
}

this code also calls the base-class: BaseFeedParser which i guess also has to be wrapped into a AsyncTask. the code for BaseFeedParser looks like:

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

public abstract class BaseFeedParser implements FeedParser {

    // names of the XML tags
    static final String CHANNEL = "channel";
    static final String PUB_DATE = "pubDate";
    static final  String DESCRIPTION = "description";
    static final  String LINK = "link";
    static final  String TITLE = "title";
    static final  String ITEM = "item";

    private final URL feedUrl;

    protected BaseFeedParser(String feedUrl){
        try {
            this.feedUrl = new URL(feedUrl);
        } catch (MalformedURLException e) {
            throw new RuntimeException(e);
        }
    }

    protected InputStream getInputStream() {
        try {
            return feedUrl.openConnection().getInputStream();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

I don't know if i'm simply dumb or having a bad day, but i don't get how this is supposted to happend. Could someone help me and my afternoon brain out to get this working?

Currently i use:

SaxFeedParser rss = new SaxFeedParser("http://www.androidster.com/android_news.rss");
messages = rss.parse();
for(Message message : messages)
{
   tv.appendText(message);
}

to process the stream, how would i do if everything was done with AsyncTask?

Kind regards

Hiam

Answer 1

I have not tried this, but it should work.
Basically the AsyncTask will retrieve the url(s) contents, parse it and publish the parsed messages.
The onProgressUpdate() is used to safely update the user interface as you please.

class ParserTask extends AsyncTask<String, List<Message>, Long> {

    protected Long doInBackground(String... urls) {
        if (urls == null || urls.length == 0)
            return null;
        for (String url : urls) {
            SaxFeedParser rss = new SaxFeedParser(url);
            List<Message> messages = rss.parse();
            publishProgress(messages);
        }
        return null; //return somethingForPostExecute;
    }

    protected void onProgressUpdate(List<Message>... messages) {
        if (messages == null || messages.length == 0)
            return;
        for (Message message : messages[0]) {
            // tv.appendText(message);
            // or call method from GUI thread (the activity)
        }
    }

    protected void onPostExecute(Long nr) {

    }
}

Then you use something like:

new ParserTask().execute("http://www.androidster.com/android_news.rss");

Or you could use multiple urls:

new ParserTask().execute(new String[]{"http://www.androidster.com/android_news.rss", "..."});