How to return an object using an async task?

Question

I am trying to return a list of tweets after parsing from an async task .... But I will not return to the archarist from the task. Can anyone suggest a solution?

public class Main extends ListActivity { String MY_APP_TAG = "com.list"; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ArrayList listItems = new ArrayList(); new myAsyncTask().execute(listItems); setListAdapter(new ArrayAdapter(this, R.layout.tweet, R.id.tweet,listItems)); ListView lv = getListView(); lv.setTextFilterEnabled(true); lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // When clicked, show a Toaster Toast.makeText(getApplicationContext(), ((TextView) view).getText(), Toast.LENGTH_SHORT).show(); } }); } private class myAsyncTask extends AsyncTask<ArrayList<Object>, Void, Void> { ArrayList<Object> listItems; ProgressDialog dialog; @Override protected void onPreExecute() { dialog = ProgressDialog.show(Main.this, "", "Loading...."); } @Override protected Void doInBackground(ArrayList<Object>... params) { String host = "api.twitter.com"; String twitterURL = "http://"+host+"/1/statuses/user_timeline.json?screen_name=i1990jain&amp;count;=10"; try { HttpClient client = new DefaultHttpClient(); BasicHttpContext localContext = new BasicHttpContext(); HttpHost targetHost = new HttpHost(host, 80, "http"); HttpGet httpget = new HttpGet(twitterURL); httpget.setHeader("Content-Type", "application/json"); HttpResponse response = client.execute(targetHost, httpget, localContext); HttpEntity entity = response.getEntity(); Object content = EntityUtils.toString(entity); Log.d(MY_APP_TAG, "OK: " + content.toString()); JSONArray ja = new JSONArray(content.toString()); for(int i = 0; i < ja.length(); i++){ JSONObject jo = ja.getJSONObject(i); listItems.add(jo.getString("text")); } } catch(Exception e) { e.printStackTrace(); } return null; } @Override protected void onPostExecute(Void result) { dialog.dismiss(); } } } 

Answer 1

how i got the job

 public class Main extends ListActivity { String MY_APP_TAG = "com.vidyut"; ArrayList<Object> list = new ArrayList<Object>(); /** Called when the activity is first created. */ @SuppressWarnings("unchecked") @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); myAsyncTask task = new myAsyncTask(); task.execute(); } private class myAsyncTask extends AsyncTask<ArrayList<Object>, ArrayList<Object>, ArrayList<Object>> { ProgressDialog dialog; @Override protected void onPreExecute() { dialog = ProgressDialog.show(Main.this, "", "Loading...."); } @Override protected ArrayList<Object> doInBackground(ArrayList<Object>... params) { String host = "api.twitter.com"; String twitterURL = "http://"+host+"/1/statuses/user_timeline.json?screen_name=i1990jain&amp;count;=10"; try { HttpClient client = new DefaultHttpClient(); BasicHttpContext localContext = new BasicHttpContext(); HttpHost targetHost = new HttpHost(host, 80, "http"); HttpGet httpget = new HttpGet(twitterURL); httpget.setHeader("Content-Type", "application/json"); HttpResponse response = client.execute(targetHost, httpget, localContext); HttpEntity entity = response.getEntity(); Object content = EntityUtils.toString(entity); Log.d(MY_APP_TAG, "OK: " + content.toString()); JSONArray ja = new JSONArray(content.toString()); for(int i = 0; i < ja.length(); i++){ JSONObject jo = ja.getJSONObject(i); list.add(jo.getString("text")); } } catch(Exception e) { e.printStackTrace(); } return list; } protected void onPostExecute(ArrayList<Object> list) { dialog.dismiss(); Log.d(MY_APP_TAG, "The returned list contains " +list.size()+ "elements"); setListAdapter(new ArrayAdapter<Object>(Main.this, R.layout.tweet, R.id.tweet,list)); ListView lv = getListView(); lv.setTextFilterEnabled(true); lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // When clicked, show a Toaster Toast.makeText(getApplicationContext(), ((TextView) view).getText(), Toast.LENGTH_SHORT).show(); } }); } } } 

Answer 2

This is AsyncTask<Params, Progress, Result> . Therefore, you should declare it as AsyncTask<Void, Void, ArrayList<Object>> .

Returns a list from the doInBackground method.

Answer 3

To update your activity with fresh data from the async stream, you can use the onProgressUpdate () / onPostExecute () method, or if you use Thead, you must use Heandler.

 //aciticty class: final Handler mHandler = new Handler(); //inside an async thread handler.post(new Runnable() { @Override public void run() { //update GUI thread here } }); 

Answer 4

Where do you want to return your results? You can access listItems in:

 protected void onPostExecute(Void result) { 

and here you should use listItems to, for example, populate your list. This method runs in the user interface thread, so it can be safely done.

In doInBackground, I don’t see listItems being initialized with any value, so it is probably null. You must create a separate instance of listItems to be used in doInBackground, and then assign it a listView inside onPostExecute.