How to move XML parsing to AsyncTask from Main Activity

Question 1

You can try as follows...

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

    // ArrayList for XML
    ArrayList<HashMap<String, String>> articlesList = new ArrayList<HashMap<String, String>>();
    LazyAdapter adapter;
    Context mContext;

    public ArticleLoaderTask(Context context) {

        mContext.this = context;

    }

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

        XMLParser parser = new XMLParser();
        String xml = parser.getXmlFromUrl(URL); // getting XML from URL
        Document doc = parser.getDomElement(xml); // getting DOM element

        NodeList nl = doc.getElementsByTagName(KEY_ARTICLE);
        // looping through all song nodes <song>
        for (int i = 0; i < nl.getLength(); i++) {
            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();
            Element e = (Element) nl.item(i);
            // adding each child node to HashMap key => value
            map.put(KEY_ID, parser.getValue(e, KEY_ID));
            map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
            map.put(KEY_CONTENT, parser.getValue(e, KEY_CONTENT));
            map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));

            // adding HashList to ArrayList
            articlesList.add(map);

        }
        return null;
    }

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

        adapter = new LazyAdapter(mContext, articlesList);
        list.setAdapter(adapter);
    }

}

In MainActivity.java...

new ArticleLoaderTask(MainActivity.this).execute();

Question 2

Try this

In activity oncreate

new AppDownloader(this).execute("");

Inside class

class AppDownloader extends AsyncTask<String, String, String> {

    Context mContext;
    ArrayList<HashMap<String, String>> articlesList= new ArrayList<HashMap<String, String>>();

public AppDownloader(Context context) {

        mContext = context;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

            // show dialog here

    }

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

  // ArrayList for XML

    XMLParser parser = new XMLParser();
    String xml = parser.getXmlFromUrl(URL); // getting XML from URL
    Document doc = parser.getDomElement(xml); // getting DOM element

    NodeList nl = doc.getElementsByTagName(KEY_ARTICLE);
    // looping through all song nodes <song>
    for (int i = 0; i < nl.getLength(); i++) {
        // creating new HashMap
        HashMap<String, String> map = new HashMap<String, String>();
        Element e = (Element) nl.item(i);
        // adding each child node to HashMap key => value
        map.put(KEY_ID, parser.getValue(e, KEY_ID));
        map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
        map.put(KEY_CONTENT, parser.getValue(e, KEY_CONTENT));
        map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));

        // adding HashList to ArrayList
        articlesList.add(map);

    }
        return null;
    }

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

     adapter = new LazyAdapter(mContext, articlesList);
    list.setAdapter(adapter);
    }

}

Question 3

Basically, as the examples suggest, you put the things you want to execute in the doInBackground() method, then you can call whatever lifecycle methods you want to do things at different times (before or after the things in your doInBackground method).

So a an simple template would be started using this command:

new MyAsyncTask.execute();

and the class would look like:

class MyAsyncTask extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // do stuff before
    }

    @Override
    protected String doInBackground(String... params) {
         // Do stuff here (off the UI thread)   
         // In your case, you can just cut and paste all your XML parsing logic here    
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        // Things you do after      
    }

}