Error in XML file from address book app

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http://stackoverflow.com – I'm doing an address book app, but I have a problem with the XML file. Everything works ok, but when I close the app, and open again, the contacts from the XML disappears. Here is the code from the main.java. I think the problem is in the method escribirXML or leerXML. public class Principal extends Activity { private ArrayList<Contacto> agenda; public static int AGREGAR = 1; public static int MODIFICAR= 2; private Adaptador adaptador; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setConten (HowTos)