I wanted to know how to refresh a ListActivity when I change/add data to it.
I first thought that ListAdapter would know when the list is chang         
        
Maybe you should do this setListAdapter(listAdapter);
Try ArrayAdapter:notifyDataSetChanged
Google docs link
If you are using an ArrayAdapter, manipulate the contents of the list through the adapter -- do not touch the underlying list. There are add(), insert(), and remove() methods on ArrayAdapter.
If you are using a CursorAdapter, run a requery() on the Cursor.