Question

Update based on @Tom solution:

SongsManager.java

public class SongsManager extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>>    {

          public interface SongsMasterCallback {         
        void showSongList(List<HashMap<String, String>> result);     
    } 

    private SongsMasterCallback  mCallback;      
    public SongsManager (SongsMasterCallback  callback) 
    {         
        mCallback = callback;    
    }   

    // Constructor
    //public SongsManager(){ }


    ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
    @Override
    protected ArrayList<HashMap<String, String>>  doInBackground(Void... params) 
          {
             //populating all the data....
       HashMap<String, String> map = new HashMap<String, String>();
             //.........
             songsList.add(map);
    }

       return songsList;
    }

    @Override
    protected void onPostExecute(ArrayList<HashMap<String, String>> result) {
        // TODO Auto-generated method stub
        //super.onPostExecute(result);
        mCallback.showSongList(result); 
    } 
}

main.java

public class Main extends Activity implements SongsMasterCallback {

public void showSongList(List<HashMap<String, String>> result) 
{
     this.songsList = (ArrayList<HashMap<String, String>>) result;     
     // then do something with the list here 
}

@Override
public void onCreate(Bundle savedInstanceState) {

  new SongsManager(this).execute();
  Log.d("songsSize", "string : "+songsList.size()); //it shows 0 ??? 

}

}

end of update

I am working on a class using AsyncTask and below is what i am getting when i try to execute

the error is on the design time so there is no LogCat

here is the class:

SongManager.java

public class SongsManager extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>> {


// Constructor
public SongsManager(){ }


@Override
    protected ArrayList<HashMap<String, String>>  doInBackground(Void... params) {
        // TODO Auto-generated method stub

        ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();

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

        NodeList nl = doc.getElementsByTagName(KEY_NAME);
        // 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
            //adding the rows into to the map...

            // adding HashList to ArrayList
            songsList.add(map);
        }

        return songsList;
    }


}

main.java file

trying to execute the AsyncTask:

public ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();
songsList = new SongsManager().execute();

here is the error:

Type mismatch: cannot convert from AsyncTask<Void,Void,ArrayList<HashMap<String,String>>> to ArrayList<HashMap<String,String>>

Answer 1

The value returned from SongsManager.execute() is not the results of the computation; it’s the AsyncTask itself. To publish your results, write a method in SongsManager:

void onPostExecute(ArrayList<HashMap<String,String>> result) {
    songsList = result; // or something similar
    // then update the UI to reflect the results
}

In this method, songsList is the variable to which you are now trying to assign the return value from new SongsManager.execute(). If this variable is not visible to the SongsManager class (e.g., it’s not a nested class of your main class), then you’ll have to arrange for a call-back:

public class SongsManager
    extends AsyncTask<Void, Void, List<Map<String,String>>
{
    public interface SongsMasterCallback {
        void showSongList(List<Map<String, String>> result);
    }

    private SongsMasterCallback mCallback;

    public SongsMaster(SongsMasterCallback callback) {
        mCallback = callback;
    }

    @Override
    protected List<Map<String, String>>  doInBackground(Void... params) {
        // as before
    }

    @Override
    protected void onPostExecute(List<Map<String, String>> result) {
        mCallback.showSongList(result);
    }
}

Then declare your activity to implement SongsManager.SongsManagerCallback and add is method:

void showSongList(List<Map<String, String>> songList) {
    this.songList = songList;
    // then do something with the list here
}