Problem returning an object from an AsyncTask

Question

I have a class (RestClient.java) that extends AsyncTask: package org.stocktwits.helper;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.AsyncTask;
import android.util.Log;

public class RestClient extends AsyncTask<String, Void, JSONObject>{
    public JSONObject jsonObj = null;
    private static String convertStreamToString(InputStream is) {
        /*
         * To convert the InputStream to String we use the BufferedReader.readLine()
         * method. We iterate until the BufferedReader return null which means
         * there's no more data to read. Each line will appended to a StringBuilder
         * and returned as String.
         */
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();

        String line = null;
        try {
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return sb.toString();
    }


    /* This is a test function which will connects to a given
     * rest service and prints it's response to Android Log with
     * labels "Praeda".
     */
    public static JSONObject connect(String url)
    {

        HttpClient httpclient = new DefaultHttpClient();


        // Prepare a request object
        HttpGet httpget = new HttpGet(url); 

        // Execute the request
        HttpResponse response;
        try {
            response = httpclient.execute(httpget);
            // Examine the response status
            Log.i("Praeda",response.getStatusLine().toString());

            // Get hold of the response entity
            HttpEntity entity = response.getEntity();

            if (entity != null) {

                // A Simple JSON Response Read
                InputStream instream = entity.getContent();
                String result= convertStreamToString(instream);

                // A Simple JSONObject Creation
                JSONObject json=new JSONObject(result);

                // Closing the input stream will trigger connection release
                instream.close();

                return json;
            }


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

        return null;
    }

    @Override
    protected JSONObject doInBackground(String... urls) {
        return connect(urls[0]);
    }

    @Override
    protected void onPostExecute(JSONObject json ) {
        this.jsonObj = json;
    }

    public void setJSONObject(JSONObject jsonFromUI){
        this.jsonObj = jsonFromUI;
    }

    public JSONObject getJSONObject(){
        return this.jsonObj;
    }

}

I am trying to execute the AsyncTask on my Main class (Main.java):

    RestClient rc = new RestClient();
    JSONObject json = new JSONObject();
    rc.setJSONObject(json);
    rc.execute(buildQuery());
    json = rc.getJSONObject();

//do some stuff with the json object
try { JSONObject query = json.getJSONObject("query");
//...
}

json is null because it is called before onPostExecute(). How can I get my JSON?

UPDATE: I need to run this try block in onPostExecute():

try {

            JSONObject query = json.getJSONObject("query");
            JSONObject results = query.getJSONObject("results");

            if (query.getString("count").equals("1")) { // YQL JSON doesn't
                // return an array for
                // single quotes
                JSONObject quote = results.getJSONObject("quote");

                Quote myQuote = new Quote();
                myQuote.setName(quote.getString("Name"));
                myQuote.setSymbol(quote.getString("Symbol"));
                myQuote.setLastTradePriceOnly(quote
                        .getString("LastTradePriceOnly"));
                myQuote.setChange(quote.getString("Change"));
                myQuote.setOpen(quote.getString("Open"));
                myQuote.setMarketCapitalization(quote
                        .getString("MarketCapitalization"));
                myQuote.setDaysHigh(quote.getString("DaysHigh"));
                myQuote.setYearHigh(quote.getString("YearHigh"));
                myQuote.setDaysLow(quote.getString("DaysLow"));
                myQuote.setYearLow(quote.getString("YearLow"));
                myQuote.setVolume(quote.getString("Volume"));
                myQuote.setAverageDailyVolume(quote
                        .getString("AverageDailyVolume"));
                myQuote.setPeRatio(quote.getString("PERatio"));
                myQuote.setDividendYield(quote.getString("DividendYield"));
                myQuote.setPercentChange(quote.getString("PercentChange"));

                quotesAdapter.add(myQuote);}

Answer 1

execute() always returns the AsyncTask itself. The object you return from doInBackground() is handed to you in onPostExecute().

Answer 2

I'm be mistaken by result of doInBackground can be consumed in onPostExecute

doInBackground(Params...), invoked on the background thread immediately after on PreExecute() finishes executing. This step is used to perform background computation that can take a long time. The parameters of the asynchronous task are passed to this step. The result of the computation must be returned by this step and will be passed back to the last step. This step can also use publishProgress(Progress...) to publish one or more units of progress. These values are published on the UI thread, in the onProgressUpdate(Progress...) step.

@Override

protected void onPostExecute(JSONObject json ) {
// DO stuff here ( it's UI thread )
 mJsonFromTheActivity = json;
}

Answer 3

If you have your asynctask as a nested inner class of your activity, you can set one of your activities variables to the result of your asynctask