Refresh ListView from ArrayAdapter

I'm using ArrayAdapter to bind my data from my ArrayListto my ListView and i use an AlertDialogto insert data into my Arraylist. My problem is that i'm unable to refresh my ListView after the changes done.

Code

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.config_hidden);
    listView=(ListView) findViewById(R.id.hiddenList);
    xmlFileManager=new XmlFileManager(this);
    addNumber=(Button) findViewById(R.id.addNum);

    addNumber.setOnClickListener(new OnClickListener() {

        public void onClick(View arg0) {

            LayoutInflater factory = LayoutInflater.from(HiddenCall.this);
            final View alertDialogView = factory.inflate(R.layout.add_number, null);
            AlertDialog.Builder adb = new AlertDialog.Builder(HiddenCall.this);
            adb.setView(alertDialogView);
            adb.setTitle(R.string.dialog_title);
            adb.setIcon(R.drawable.phone);

            final AlertDialog alertDialog = adb.create();

            adb.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    numberToAdd=(EditText) alertDialogView.findViewById(R.id.numberToAdd);
                    String number = numberToAdd.getText().toString();
                    if(number.length()>0){
                        xmlFileManager.addNumberToXml(number , HIDDEN_NUMBER_TYPE);
                        adapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_list_item_1, xmlFileManager.getHiddenNumbers());
                        adapter.setNotifyOnChange(true);
                        adapter.notifyDataSetChanged();
                    }
                } });

            adb.setNegativeButton(R.string.cancel, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    alertDialog.dismiss();
                } });
            adb.show();
        }
    });
    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, xmlFileManager.getHiddenNumbers());
    adapter.notifyDataSetChanged();
    adapter.setNotifyOnChange(true);
    listView.setAdapter(adapter);
}