How do I retrieve the data from AsyncTasks doInBackground()?

Issue

I'll keep this one as simple as I can.

I have a method in my control layer that uses a class CallServiceTask that extends AsyncTask. When calling new CallServiceTask().execute(parameters)
How do I retrieve the data returned from doInBackground? All the tutorials I've found use the class that extends AsyncTask directly from their Activity.
My problem is a little bit more complex than that.
All I want is to take the Object[] returned by doInBackground and set it to the private data members of my RestClient class.

CallServiceTask looks like this :

    private class CallServiceTask extends AsyncTask<Object, Void, Object[]>
{

    protected Object[] doInBackground(Object... params) 
    {
        HttpUriRequest req = (HttpUriRequest) params[0];
        String url = (String) params[1];

        return executeRequest(req, url);
    }
}

And my RestClient class looks like this:

public class RestClient
{

private ArrayList <NameValuePair> params;
private ArrayList <NameValuePair> headers;

private JSONObject jsonData;

private Object[] rtnData;

private String url;

private boolean connError;

public int getResponseCode() {
    return responseCode;
}

/**
 * 
 * @return  the result of whether the login was successful by looking at the response parameter of the JSON object. 
 */
public Boolean DidLoginSucceed()
{
    // Will Crash on socket error
        return ((JSONObject) rtnData[0]).optBoolean("response");
}

public String GetToken()
{
    return jsonData.optString("token");
}

public RestClient(String url)
{
    this.url = url;
    params = new ArrayList<NameValuePair>();
    headers = new ArrayList<NameValuePair>();
    rtnData = new Object[]{ new JSONObject() , Boolean.TRUE  };
}

public void AddParam(String name, String value)
{
    params.add(new BasicNameValuePair(name, value));
}

public void AddHeader(String name, String value)
{
    headers.add(new BasicNameValuePair(name, value));
}

/**
 * This method will execute, call the service and instantiate the JSON Object through executeRequest().
 * 
 * @param method    an enum defining which method you wish to execute.
 * @throws Exception
 */
public void ExecuteCall(RequestMethod method) throws Exception
{
    Object[] parameters = new Object[]{ new HttpGet() , new String("") };
    switch(method) {
        case GET:
        {
            //add parameters
            String combinedParams = "";
            if(!params.isEmpty()){
                combinedParams += "?";
                for(NameValuePair p : params)
                {
                    String paramString = p.getName() + "=" + URLEncoder.encode(p.getValue());
                    if(combinedParams.length() > 1)
                    {
                        combinedParams  +=  "&" + paramString;
                    }
                    else
                    {
                        combinedParams += paramString;
                    }
                }
            }

            HttpGet request = new HttpGet(url + combinedParams);

            //add headers
            for(NameValuePair h : headers)
            {
                request.addHeader(h.getName(), h.getValue());
            }
            parameters[0] = request;
            parameters[1] = url;

            new CallServiceTask().execute(parameters);

            jsonData = ((JSONObject) rtnData[0]).optJSONObject("data");
            connError = (Boolean) rtnData[1];
            break;

        }
        case POST:
        {
            HttpPost request = new HttpPost(url);

            //add headers
            for(NameValuePair h : headers)
            {
                request.addHeader(h.getName(), h.getValue());
            }

            if(!params.isEmpty()){
                request.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));
            }
            new CallServiceTask().execute(request, url);
            break;
        }
    }
}

private Object[] executeRequest(HttpUriRequest request, String url)
{
    HttpClient client = new DefaultHttpClient();
    client = getNewHttpClient();

    HttpResponse httpResponse;

    try {
        httpResponse = client.execute(request);
        HttpEntity entity = httpResponse.getEntity();

        if (entity != null) {

            InputStream instream = entity.getContent();
            String response = convertStreamToString(instream);
            try {
                rtnData[0] = new JSONObject(response);
                rtnData[1] = false;

            } catch (JSONException e1) {
                rtnData[1] = true;
                e1.printStackTrace();
            }

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

    } catch (ClientProtocolException e)  {
        client.getConnectionManager().shutdown();
        e.printStackTrace();
    } catch (IOException e) {
        client.getConnectionManager().shutdown();
        e.printStackTrace();
    }
    return rtnData;
}


private static String convertStreamToString(InputStream is) {

    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();
}

/**
 * Custom HTTP Client accepting all SSL Certified Web Services.
 * 
 * @return n HttpClient object.
 */
public HttpClient getNewHttpClient() {
    try {
        KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
        trustStore.load(null, null);

        SSLSocketFactory sf = new MySSLSocketFactory(trustStore);
        sf.setHostnameVerifier(SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);

        HttpParams params = new BasicHttpParams();
        HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
        HttpProtocolParams.setContentCharset(params, HTTP.UTF_8);

        SchemeRegistry registry = new SchemeRegistry();
        registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
        registry.register(new Scheme("https", sf, 443));

        ClientConnectionManager ccm = new ThreadSafeClientConnManager(params, registry);

        return new DefaultHttpClient(ccm, params);
    } catch (Exception e) {
        return new DefaultHttpClient();
    }
}

Solution

The only way to do this is using a CallBack. You can do something like this:

new CallServiceTask(this).execute(request, url);

Then in your CallServiceTask add a local class variable and call a method from that class in your onPostExecute:

private class CallServiceTask extends AsyncTask<Object, Void, Object[]>
{
    RestClient caller;

    CallServiceTask(RestClient caller) {
        this.caller = caller;
    }


    protected Object[] doInBackground(Object... params) 
    {
        HttpUriRequest req = (HttpUriRequest) params[0];
        String url = (String) params[1];
        return executeRequest(req, url);
    }

    protected onPostExecute(Object result) {
        caller.onBackgroundTaskCompleted(result);
    }
}

Then simply use the Object as you like in the onBackgroundTaskCompleted() method in your RestClient class.

A more elegant and extendible solution would be to use interfaces. For an example implementation see this library. I've just started it but it has an example of what you want.

Answered By - Saad Farooq