SetListAdapter works only at debug mode

Question

I am working on an app which performs (in an AsyncTask) a query to a remote server obtaining a JSON string. To show the data on my ListView i have extended an ArrayAdapter.

When i execute my app, from the LogCat i can see that data is retrieved correctly but not shown in the ListView.

The only way i have to make everything work (and data be shown on the ListView) is by running the app in Debug mode, set a breakpoint on the line

myListView.setAdapter(myAdapter);

wait for a couple seconds and then resume the application. After this procedure, everything works correctly.

Why is this happening?

Is the AsyncTask the right way for such a long operation, or should I use some other approach (but i don't know which one!).

Here is the MainActivity code

public class MainActivityFragment extends Fragment {

private List<Station> stationList = new ArrayList<Station>();
private StationAdapter stationsAdapter;
private ProgressDialog pd;
private String LOG_TAG = "ProvaAsyncTask";

public MainActivityFragment() {
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    mioAsync mioTask = new mioAsync();
    mioTask.execute();


    stationsAdapter = new StationAdapter(stationList, getActivity());

    ListView stationsListView = (ListView) rootView.findViewById(R.id.miaListView);

    stationsListView.setAdapter(stationsAdapter);

    return rootView;
}


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

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

        // Creo la ProgressDialog che precede il caricamento dei dati
        pd = new ProgressDialog(getActivity());
        pd.setMessage(MainActivityFragment.this.getString(R.string.preloader_stations_list));
        pd.show();
    }


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

        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;

        String forecastJsonStr = null;

        try {

            URL url = new URL("*remoteserver*");

            // Create the request to the server, and open the connection
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();

            // Read the input stream into a String
            InputStream inputStream = urlConnection.getInputStream();
            StringBuffer buffer = new StringBuffer();
            if (inputStream == null) {
                // Nothing to do.
                return null;
            }
            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;
            while ((line = reader.readLine()) != null) {                    
                buffer.append(line + "\n");
            }

            if (buffer.length() == 0) {
                // Stream was empty.  No point in parsing.
                return null;
            }
            forecastJsonStr = buffer.toString();

        } catch (IOException e) {
            Log.e(LOG_TAG, "Error ", e);                
            return null;
        } finally{
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            if (reader != null) {
                try {
                    reader.close();
                } catch (final IOException e) {
                    Log.e(LOG_TAG, "Error closing stream", e);
                }
            }
        }

        try{
            getStationsListFromJson(forecastJsonStr);

        } catch (JSONException e) {
            Log.e(LOG_TAG, e.getMessage(), e);
            e.printStackTrace();
        }

        return null;

    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        pd.dismiss();
    }


    private void getStationsListFromJson(String stationsJsonStr) throws JSONException {

        JSONArray stationsArray = new JSONArray(stationsJsonStr);

        String nomeStaz;
        String numSat;

        stationList.clear();
        for (int i = 0; i < stationsArray.length(); i++) {
            JSONObject j = stationsArray.optJSONObject(i);
            Iterator it = j.keys();

            while (it.hasNext()) {
                String n = it.next().toString();
                numSat = j.getString(n) + " stazioni";
                n = it.next().toString();
                nomeStaz = j.getString(n);
                stationList.add(new Station(nomeStaz, numSat));
            }
        }

    }

}
}

The JSON string i get in return is like this

[{"nome":"Station1","satelliti":"11"},{"nome":"Station2","satelliti":"9"},{"nome":"Station3","satelliti":"8"}]

Here is where i extend the ArrayList

public class StationAdapter extends ArrayAdapter<Station> {

private List<Station> stationsList;
private Context context;

public StationAdapter(List<Station> lista, Context cont){
    super(cont, R.layout.listitems, lista);
    this.stationsList = lista;
    this.context = cont;
}

public int getCount() {
    return stationsList.size();
}

public Station getItem(int position) {
    return stationsList.get(position);
}

public long getItemId(int position) {
    return stationsList.get(position).hashCode();
}

public View getView(int position, View convertView, ViewGroup parent){
    View v = convertView;

    StationHolder holder = new StationHolder();

    // controllo che il convertview non sia null
    if (convertView == null){

        // This a new view we inflate the new layout
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        v = inflater.inflate(R.layout.listitems, null);

        // Now we can fill the layout with the right values
        TextView stationName = (TextView) v.findViewById(R.id.testataUno);
        TextView satellitesNumber = (TextView) v.findViewById(R.id.testataDue);

        holder.stationNameView = stationName;
        holder.satellitesNumberView = satellitesNumber;

        v.setTag(holder);



    } else {
        holder = (StationHolder) v.getTag();
    }

    Station p = stationsList.get(position);
    holder.stationNameView.setText(p.getName());
    holder.satellitesNumberView.setText("" + p.getSatellites());

    return v;
}


/* *********************************
 * We use the holder pattern
 * It makes the view faster and avoid finding the component
 * **********************************/

private static class StationHolder {
    public TextView stationNameView;
    public TextView satellitesNumberView;
}

}

Here is the Station code

public class Station {

private String name;
private String satellites;

public Station(String nome, String satelliti){
    this.name = nome;
    this.satellites = satelliti;
}

public String getName(){
    return this.name;
}

public String getSatellites(){
    return this.satellites;
}

public void setName(String nome){
    this.name = nome;
}

public void setSatellites(String satelliti){
    this.satellites = satelliti;
}

}

Answer 1

You got the flow broken. It works in debug mode only because you stop execution of UI thread on your breakpoint, but line before your breakpoint you fired AsyncTask, and as this is not stopped, it downloads the data while you enjoy your breakpoint. You most likely assumed that AsyncTask (which is abbreviation of Asynchronous Task) is... well... synchronous. It's not. Your main code will not wait for asynctask,it will start it and continue. You need to rework your code and in asynctask's onPostExecute() method update your dataset based on downloaded content and then call notifyDatasetChanged() on your list's adapter. That should trigger list refresh.