Need an explanation : how to use AsyncTask?

Question

I have a XML file containing some data, so I created a class representing it :

public class MyData
{
    ArrayList<SpecialData> list;
    int currentPage, totalPages;
}

As you can guess I have a list of SpecialData items, each one containing many fields, and currentPage/totalPages are two unique values in the XML file. I need to get and parse the XML file asynchronously, so I created this class :

class GetXMLTask extends AsyncTask<String, Void, MyData>
{
    @Override
    protected MyData doInBackground(String... params)
    {
        MyData md = null;
        // Getting/parsing data
        return md;
    }
}

I gave it a try and the problem doesn't come from here because I correctly parse my XML file and my MyData object is perfect. But then I use this task like this in my main Activity class :

MyData md = null;
GetXMLTask task = new GetXMLTask(this);
task.execute(new String[]{url});
// How can this change my md object?

This may be very silly but I simply don't know how to link my MyData instance from my main class to the one that I get with AsyncTask. What should I do? Thanks.

Answer 1

Override AsyncTask's onPostExecute method:

protected void onPostExecute(MyData result) {
     md = result;
 }

Note that this assumes your AsyncTask is an inner class to your activity. If that isn't the case, you can pass in a reference to your Activity in the constructor to your AsyncTask. In those cases, you should be careful to use a WeakReference to your Activity to prevent resource leaks:

GetXMLTask(MyActivity activity)
{
    this.mActivity = new WeakReference<MyActivity>(activity);
}

protected void onPostExecute(MyData result)
{
     MyActivity activity = this.mActivity.get();
     if (activity == null) // Activity was destroyed due to orientation change, etc.
         return;
     activity.updateUiFromXml(result);
 }