Question

I made an application for Android that originally targeted a lower version (2.3). After I got my proof-of-concept working, I tried to get it to work on Android 4. That’s when I got the NetworkOnMainThread exception.

After doing some research, I quickly found the AsyncTask, which sounded awesome. The problem is, I’m having a hard time wrapping my mind around it. For instance, here’s my original code:

public void Refresh(Context c)
{
    SummaryModel model = MobileController.FetchSummary(c);

    TextView txtCurrentWeight = (TextView)findViewById(R.id.txtCurrentWeight);
    TextView txtWeightChange = (TextView)findViewById(R.id.txtWeightChange);
    TextView txtAvgPerWeek = (TextView)findViewById(R.id.txtAvgPerWeek);

    if(model.ErrorMessage == "")
    {
        txtCurrentWeight.setText(model.CurrentWeight);
        txtWeightChange.setText(model.WeightChange);
        txtAvgPerWeek.setText(model.Average);
    }
    else
    {
        Toast.makeText(c, model.ErrorMessage, Toast.LENGTH_LONG).show();

        txtCurrentWeight.setText("");
        txtWeightChange.setText("");
        txtAvgPerWeek.setText("");
    }
}

I created an AsychTask like this:

public class WebMethodTask extends AsyncTask<Object, Integer, Object> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
    }

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

        SummaryModel model = (SummaryModel)result;
        // Can't seem to access UI items here??

    }

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

        Context c = (Context)params[0];
        return MobileController.FetchSummary(c);
    }
}

How do I access the UI items from the onPostExecute method? Or, do I have the wrong idea on how to use AsyncTask?

Thanks!

Answer 1

You should be able to accessUI where you put your comments (in the postExecute method)

Additionally, I would suggest to use more specialized class with for AsyncTask, so that your code looks better :

public class WebMethodTask extends AsyncTask<Object, Integer, SummaryModel> {

    private Activity source;
    public WebMethodTask(Activity activity) {
        this.source=activity;
        }

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

    @Override
    protected void onProgressUpdate(Integer... values) {
        super.onProgressUpdate(values);
    }

    @Override
    protected void onPostExecute(SummaryModel model) {
        super.onPostExecute(model );

        TextView txtCurrentWeight = (TextView)source.findViewById(R.id.txtCurrentWeight);
        TextView txtWeightChange = (TextView)source.findViewById(R.id.txtWeightChange);
        TextView txtAvgPerWeek = (TextView)source.findViewById(R.id.txtAvgPerWeek);

        if(model.ErrorMessage.length()==0)
        {
            txtCurrentWeight.setText(model.CurrentWeight);
            txtWeightChange.setText(model.WeightChange);
            txtAvgPerWeek.setText(model.Average);
        }
        else
        {
            Toast.makeText(c, model.ErrorMessage, Toast.LENGTH_LONG).show();

            txtCurrentWeight.setText("");
            txtWeightChange.setText("");
            txtAvgPerWeek.setText("");
        }

    }

    @Override
    protected SummaryModel doInBackground(Context ... params) {
        Context c = params[0];
        return MobileController.FetchSummary(c);
    }
}

Edit : Added a reference to your activity, to take your last comment into account.

---

However, if you acynctask can be long, it’s maybe not a very good idea to keep a reference on an activity.

It would be a better design to create a listenerclass that will accept some displayModel(CummaryModel) method, and whose responsability is to cal the setText methods if the activity has not been paused / stopped in the meanwhile…