I made a simple AsyncTask class to display data in ListView with the help of this stackoverflow question. But the AsyncTask onPostExecute is not being called. This is my code: public class Start extends SherlockActivity { // JSON Node names private static final String TAG_ID = "id"; private static final String TAG_NAME = "name"; // category JSONArray JSONArray category = null; private ListView lv; @Override public void onCreate(Bundle savedInstanceState) { setTheme(SampleList.THEME); //Used for theme switching in samples super.onCreate(savedInstanceState); setContentView(R.layout.test); new MyAsyncTask().execute("http://...."); // Launching new screen on Selecting Single ListItem lv.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // getting values from selected ListItem String name = ((TextView) view.findViewById(R.id.name)).getText().toString(); String cost = ((TextView) view.findViewById(R.id.mail)).getText().toString(); // Starting new intent Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); in.putExtra("categoryname", name); System.out.println(cost); in.putExtra("categoryid", cost); startActivity(in); } }); } public class MyAsyncTask extends AsyncTask<String, Void, ArrayList<HashMap<String, String>> > { // Hashmap for ListView ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>(); @Override protected ArrayList<HashMap<String, String>> doInBackground(String... params) { // Creating JSON Parser instance JSONParser jParser = new JSONParser(); // getting JSON string from URL category = jParser.getJSONArrayFromUrl(params[0]); try { // looping through All Contacts for(int i = 0; i < category.length(); i++){ JSONObject c = category.getJSONObject(i); // Storing each json item in variable String id = c.getString(TAG_ID); String name = c.getString(TAG_NAME); // creating new HashMap HashMap<String, String> map = new HashMap<String, String>(); // adding each child node to HashMap key => value map.put(TAG_ID, id); map.put(TAG_NAME, name); // adding HashList to ArrayList contactList.add(map); } } catch (JSONException e) { Log.e("log_tag", "Error parsing data "+e.toString()); } return contactList; } @Override protected void onPostExecute(ArrayList<HashMap<String, String>> result) { ListAdapter adapter = new SimpleAdapter(Start.this, result , R.layout.list_item, new String[] { TAG_NAME, TAG_ID }, new int[] { R.id.name, R.id.mail }); // selecting single ListView item lv = (ListView) findViewById(R.id.ListView); lv.setAdapter(adapter); } } } Eclipse: 11-25 11:40:31.896: E/AndroidRuntime(917): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.essentials/de.main.Start}: java.lang.NullPointerException