Trying to implement AsyncTask to make an http request

Question

I've been trying to implement asynctask to make about 30 http requests to find the distance between two locations using a JSON object and the distance matrix api. The code I've written works when called from the main UI thread, but when I try to run it from the Async Task and save the distances to an array I just end up with an array full of null values. Any advice? (Note: This code was initially written by someone else at my work, and I've merely copy pasted it and changed a few lines to work with my app. So, there may be some unnecessary bits that I'm unaware of. Feel free to point them out)

class DistanceFinder extends AsyncTask<String[], Void, String[]>
{   

        @Override
        protected String[] doInBackground(String[]... locations) 
        {

        String baseURL="https://maps.googleapis.com/maps/api/distancematrix/json?origins=";
        String[] distances = new String[locations[1].length];


        for(int i = 1;i<locations.length;i++)
        {
            String url = baseURL + locations[0][0].replace(" ","+") + "&destinations=" + locations[1][i].replace(' ', '+') + "&sensor=true&units=imperial";
            HttpClient httpclient = new DefaultHttpClient();
            HttpResponse response;
            String responseString = "";
            boolean internet;
            try 
            {
                    response = httpclient.execute(new HttpGet(url));
                    StatusLine statusLine = response.getStatusLine();
                    if(statusLine.getStatusCode() == HttpStatus.SC_OK)
                    {
                        ByteArrayOutputStream out = new ByteArrayOutputStream();
                        response.getEntity().writeTo(out);
                        out.close();
                        responseString = out.toString();   
                        internet=true;

                    } 
                    else
                    { 
                            response.getEntity().getContent().close();
                             throw new IOException(statusLine.getReasonPhrase());
                    } 
            } catch (ClientProtocolException e) 
            {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    internet=false;
                    Toast.makeText(getApplicationContext(), "Please connect to internet", Toast.LENGTH_LONG).show();

            } 
            catch (IOException e) 
            {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    internet=false;
                    Toast.makeText(getApplicationContext(),"Please connect to internet", Toast.LENGTH_LONG).show();

            }

            if(internet){
                try 
                {
                    JSONObject jsonObj = new JSONObject(responseString);
                    JSONArray rows = jsonObj.getJSONArray("rows");
                    JSONObject inRows=rows.getJSONObject(0);
                    JSONArray elements = inRows.getJSONArray("elements");
                    JSONObject inElements=elements.getJSONObject(0);
                    JSONObject distance= inElements.getJSONObject("distance");
                    distances[i] = distance.getString("text");

                } 
                catch (JSONException e) 
                {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

        }
        return distances;

    }

    @Override
    protected void onPostExecute(String[] result) 
    {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        distancesList = result;
    }

    @Override
    protected void onPreExecute() 
    {
        // TODO Auto-generated method stub
        super.onPreExecute();
    }

}

Answer 1

Your problem is with you for loop

for(int i = 1;i<locations.length;i++)

First, you should start from 0, unless your first cell doesn't store a String you wish you check the distance to.

Second, your for loop should be

for(int i = 0;i<locations[0].length;i++)

Right now you're checking cells [1][0] and that's it, because the loop ends.

I tested it with manually entered locations and it works.

Also, just to make things easier for you to debug, You should really get used to using Log.d() . It really helps figuring out errors. I used it in your code and saw that the loop only gets executed once.

Good luck

Ps, as mentioned in one of the comments, remove the onPreExecute() . You don't use it.