Below
ListView lv = getListView();
Add
adapter = new SimpleAdapter(
MainActivity.this, contactList,
R.layout.list_item, new String[] { TAG_NAME, TAG_PID
}, new int[] { R.id.name,
R.id.pid});
setListAdapter(adapter);
Declare your adapter as a private variable
private SimpleAdapter adapter;
Then in your onPostExecute method call
adapter.notifyDataSetChanged();
Rather than setting a new adapter each time with every call, you simply want to let the adapter know that new data has been added. This will then tell your list view to reevaluate itsself, and then you will see the new data appear.