Updating listview with arrayadapter [duplicate]

Hi testing a sample gcm application but everytime i send a message i cant add another value in listview. What happens is the previous message is being replaced by the new one.

Here is my code:

Sorry for poor coding.

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_memo);
    getActionBar().setDisplayHomeAsUpEnabled(true);
    list1 = (ListView)findViewById(R.id.listView1);

    registerReceiver(HandleMemoReceiver, new IntentFilter(DISPLAY_MESSAGE_ACTION));

}
private final BroadcastReceiver HandleMemoReceiver = new BroadcastReceiver(){

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO Auto-generated method stub

        String newMessage = intent.getExtras().getString(EXTRA_MESSAGE);
        //memo.append(newMessage + "\n");
        ArrayList<String> nm = new ArrayList<String>();

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(Memo.this,  android.R.layout.simple_list_item_1,nm);
        list1.setAdapter(adapter);
        adapter.add(newMessage);
        adapter.notifyDataSetChanged();
    }
};

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.memo, menu);
    return true;
}
public void onBackPressed() {
    finish();//go back to the previous Activity
    overridePendingTransition(R.anim.pull_in_left, R.anim.push_out_right);
}