Question

I am a beginner in Android, and I am writing a short program to download a JSON feed from URL and parse it. I use AsyncTask to do the downloading.

The doInBackground() part seems to work well. Then I set my breakpoint to onPostExecute(), it can even stop at parseJSON(result), and ‘result’ is showing the correct json string downloaded. But when I try to step into parseJSON(result), it will NOT step into the function correctly(either throw JSONException directly or go to some random lines within parseJSON(result)).

From DDMS log it’s not showing any valuable information as well.

How might I find what the problem is? Is it because I used onPostExecute() incorrectly, or parseJSON() has some problem?

public class MainActivity extends Activity {

    private listItem[] items;

    public class listItem {
        String title;
        String description;
        String imageHref;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        items = new listItem[50];

        new DownloadJsonFeed().execute("http://dl.dropbox.com/u/10168342/facts.json");
    }

    private class DownloadJsonFeed extends AsyncTask<String, Void, String> {
        @Override
        protected String doInBackground(String... params) {

            try {
                return downloadUrl(params[0]);
            } catch (IOException e) {
                return "Unable to retrieve json feed. URL may be invalid.";
            }
        }

        @Override
        protected void onPostExecute(String result) {
            try {
                parseJSON(result);          // Here !!!!!!
            } catch (JSONException e) {
            }
        }
    }

    private String downloadUrl(String myurl) throws IOException {
        InputStream is = null;

        try {
            URL url = new URL(myurl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("GET");
            conn.setDoInput(true);
            conn.connect();
            is = conn.getInputStream();

            // Convert the InputStream into a string
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();
            String line = null;

            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
            is.close();
            return sb.toString();
        } finally {
            if (is != null) {
                is.close();
            } 
        }
    }

    private void parseJSON(String feed) throws JSONException {
            JSONObject json_obj = new JSONObject(feed);
            title = json_obj.getString("title");
            String rows = json_obj.getString("rows");

            JSONArray jArray = new JSONArray(rows);
            for (int i = 0; i < jArray.length(); i++) {
                JSONObject tmp = jArray.getJSONObject(i);
                items[i].title = tmp.getString("title");
                items[i].description = tmp.getString("description");
                items[i].imageHref = tmp.getString("imageHref");
            }
    }

Answer 1

I think you didn’t get the JSON array right. The json_obj.getString will give you an String instead an array.

Try to change as follows:

  private void parseJSON(String feed) throws JSONException {
            JSONObject json_obj = new JSONObject(feed);
            title = json_obj.getString("title");
            String rows = json_obj.getString("rows");

            JSONArray jArray = json_obj.getJSONArray("rows"); //<---- change this line
            for (int i = 0; i < jArray.length(); i++) {
                JSONObject tmp = jArray.getJSONObject(i);
                items[i].title = tmp.getString("title");
                items[i].description = tmp.getString("description");
                items[i].imageHref = tmp.getString("imageHref");
            }
    }