Wednesday, July 7, 2010

Read RSS in background, using AsyncTask

Here is a further work of the previous exercise "Simple RSS Reader, with Options Menu to reload RSS", with the help of "AsyncTask: perform background operations and publish results on the UI thread". The original readRss() method is broke into three section, preReadRss(), readRss() and displayRss(). and are called inside AsyncTask's onPreExecute() , doInBackground() and onPostExecute(). Such that the time-consume task can be moved to run in background.

Read RSS in background, using AsyncTask

AndroidRssReader.java
package com.exercise.AndroidRssReader;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Calendar;
import java.util.List;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidRssReader extends ListActivity {

public class RssLoadingTask extends AsyncTask<Void, Void, Void> {

@Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
displayRss();
}

@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
preReadRss();
}

@Override
protected void onProgressUpdate(Void... values) {
// TODO Auto-generated method stub
//super.onProgressUpdate(values);
}

@Override
protected Void doInBackground(Void... arg0) {
// TODO Auto-generated method stub
readRss();
return null;
}

}

private RSSFeed myRssFeed = null;

TextView feedTitle;
TextView feedDescribtion;
TextView feedPubdate;
TextView feedLink;

public class MyCustomAdapter extends ArrayAdapter<RSSItem> {

public MyCustomAdapter(Context context, int textViewResourceId,
List<RSSItem> list) {
super(context, textViewResourceId, list);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
//return super.getView(position, convertView, parent);

View row = convertView;

if(row==null){
LayoutInflater inflater=getLayoutInflater();
row=inflater.inflate(R.layout.row, parent, false);
}

TextView listTitle=(TextView)row.findViewById(R.id.listtitle);
listTitle.setText(myRssFeed.getList().get(position).getTitle());
TextView listPubdate=(TextView)row.findViewById(R.id.listpubdate);
listPubdate.setText(myRssFeed.getList().get(position).getPubdate());

if (position%2 == 0){
listTitle.setBackgroundColor(0xff101010);
listPubdate.setBackgroundColor(0xff101010);
}
else{
listTitle.setBackgroundColor(0xff080808);
listPubdate.setBackgroundColor(0xff080808);
}

return row;
}
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

feedTitle = (TextView)findViewById(R.id.feedtitle);
feedDescribtion = (TextView)findViewById(R.id.feeddescribtion);
feedPubdate = (TextView)findViewById(R.id.feedpubdate);
feedLink = (TextView)findViewById(R.id.feedlink);

startReadRss();
}

private void startReadRss(){
new RssLoadingTask().execute();
}

private void preReadRss()
{
feedTitle.setText("--- wait ---");
feedDescribtion.setText("");
feedPubdate.setText("");
feedLink.setText("");
setListAdapter(null);

Toast.makeText(this, "Reading RSS, Please wait.", Toast.LENGTH_LONG).show();
}

private void readRss(){



try {
URL rssUrl = new URL("http://www.gov.hk/en/about/rss/govhkrss.data.xml");
SAXParserFactory mySAXParserFactory = SAXParserFactory.newInstance();
SAXParser mySAXParser = mySAXParserFactory.newSAXParser();
XMLReader myXMLReader = mySAXParser.getXMLReader();
RSSHandler myRSSHandler = new RSSHandler();
myXMLReader.setContentHandler(myRSSHandler);
InputSource myInputSource = new InputSource(rssUrl.openStream());
myXMLReader.parse(myInputSource);

myRssFeed = myRSSHandler.getFeed();

} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

private void displayRss()
{
if (myRssFeed!=null)
{
Calendar c = Calendar.getInstance();
String strCurrentTiime = "\n(Time of Reading - "
+ c.get(Calendar.HOUR_OF_DAY)
+ " : "
+ c.get(Calendar.MINUTE) + ")\n";

feedTitle.setText(myRssFeed.getTitle() + strCurrentTiime);
feedDescribtion.setText(myRssFeed.getDescription());
feedPubdate.setText(myRssFeed.getPubdate());
feedLink.setText(myRssFeed.getLink());

MyCustomAdapter adapter =
new MyCustomAdapter(this, R.layout.row, myRssFeed.getList());
setListAdapter(adapter);

}
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
Intent intent = new Intent(this,ShowDetails.class);
Bundle bundle = new Bundle();
bundle.putString("keyTitle", myRssFeed.getItem(position).getTitle());
bundle.putString("keyDescription", myRssFeed.getItem(position).getDescription());
bundle.putString("keyLink", myRssFeed.getItem(position).getLink());
bundle.putString("keyPubdate", myRssFeed.getItem(position).getPubdate());
intent.putExtras(bundle);
startActivity(intent);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// TODO Auto-generated method stub
menu.add(0, 0, 0, "Reload");
return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
// TODO Auto-generated method stub
switch(item.getItemId()){
case (0): startReadRss();
break;
default:
break;
}

return true;
}
}


Download the files.

5 comments:

Martijn said...

Hi, just a smalle question: do you have any idea on how to implement image parsing? I mean: get the url of an image and after that display it in the listview?? Thanks!

Android Er said...

hello Martijn,

please read Load ListView in background AsyncTask, to load image from internet.

harshadura a.k.a. Durapix said...

thanks for maintaining this kinda awesome android development site. I learnt lot stuff from here.. thanks lot admin!!

Rahul said...

How to get the XML file for this code? Is there any link or something like that?

Andr.oid Eric said...

hello Rahul,

Please start reading here: A simple RSS reader, using Android's org.xml.sax package.

It's a series of exercise step-by-step. And also, you can download the files, from the link in the post.