Refresh ListView when Device receives GCM IntentService Message - service

Question

My app is able to receive messages from GCM and saves the messages to the SQLlite database on the phone. The messages are viewable in a activity that has a listview.
In the code below, the onPause() function refreshes the listView. This is not a good implementation because it only works if the activity is not displayed at the time of the update. If the activity is displayed at the time of an update, the list is static and does not update.
Questions:
How to I update the listview when the activity is being displayed? Or is there a way to use a background service to update the adapter, so that whenever the activity is displayed, it always shows the newest data.
is this kind of functionality currently not possible with android and I'll need to implement something else like 'pull-to-refresh'?
refreshing listview in OnResume() crashes the application, and shows a null pointer exception.
Activity:
public class NotesView extends Activity implements OnItemClickListener {
ListView listView;
NoteAdapter objAdapter;
NotificationsDatabase db = new NotificationsDatabase(this);
List<Notes> listAlerts;
String note;
String time;
TextView noteView;
TextView timeView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.note);
listView = (ListView) findViewById(R.id.notelist);
listView.setOnItemClickListener(this);
noteView = (TextView) findViewById(R.id.noteDisplay);
timeView = (TextView) findViewById(R.id.notetimeStampDisplay);
new MyTask().execute();
}
// My AsyncTask start...
class MyTask extends AsyncTask<Void, Void, List<Notes>> {
ProgressDialog pDialog;
#Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(NotesView.this);
pDialog.setMessage("Loading...");
pDialog.setCancelable(false);
pDialog.show();
if (isCancelled()) {
this.cancel(true);
}
}
#Override
protected List<Notes> doInBackground(Void... params) {
db.open();
listAlerts = db.getData();
if (isCancelled()) {
this.cancel(true);
}
return null;
}
protected void onPostExecute(List<Notes> alerts) {
if (null != pDialog && pDialog.isShowing()) {
pDialog.dismiss();
}
db.close();
setAdapterToListview();
}
}// end myTask
public void setAdapterToListview() {
objAdapter = new NoteAdapter(NotesView.this, R.layout.row_notes, listAlerts);
objAdapter.sortByNoteDesc();
objAdapter.notifyDataSetChanged();
listView.setAdapter(objAdapter);
}
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
Intent intent = new Intent(
NotesView.this.getApplicationContext(),
TabBarExample.class);
intent.putExtra("goToTab", "Alerts");
startActivity(intent);
return true;
}
return super.onKeyDown(keyCode, event);
}
public void onItemClick(AdapterView<?> parent, View viewDel, int position,
long id) {
for (int i = 0; i < 1; i++) {
Notes item = listAlerts.get(position);
int ids = item.getId();
note = item.getNote();
time = item.getTimeStamp();
}
System.out.println(note + " " + time);
//
}
#Override
protected void onResume() {
super.onResume();
}
#Override
protected void onPause() {
super.onPause();
setContentView(R.layout.note);
listView = (ListView) findViewById(R.id.notelist);
listView.setAdapter(null);
listView.setOnItemClickListener(this);
noteView = (TextView) findViewById(R.id.noteDisplay);
timeView = (TextView) findViewById(R.id.notetimeStampDisplay);
new MyTask().execute();
}
#Override
protected void onDestroy() {
}
}
Code snippets From GCMIntentService
#Override
protected void onMessage(Context context, Intent intent) {
Log.i(TAG, "Received message");
//String message = getString(R.string.gcm_message);
System.out.println("onMessage: ");
Bundle extras = intent.getExtras();
String message = extras.getString("message");
String event_id_from_server = extras.getString("server_id");
// displayMessage(context, message);
generateNotification(context, message);
saveMsg(message);
System.out.println("server id is " + event_id_from_server);
if (event_id_from_server != null) {
updateLocalDatabase(event_id_from_server);
}
}
public void saveMsg(String msg) {
boolean worked = true;
try {
NotificationsDatabase entry = new NotificationsDatabase(GCMIntentService.this);
entry.open();
java.util.Date date = new java.util.Date();
Timestamp x = new Timestamp(date.getTime());
String timeStamp = x.toLocaleString();
entry.createEntry(msg, timeStamp);
entry.close();
//update adapter service
} catch (Exception e) {
worked = false;
String error = e.toString();
System.out.println(error);
} finally {
if (worked) {
}
}
}

Answer 1

I cleaned up your code a little bit. Basically all the view assignments should be done once in onCreate, while the loading of the data should be done in onResume(). See if this helps:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.note);
listView = (ListView) findViewById(R.id.notelist);
listView.setAdapter(null);
listView.setOnItemClickListener(this);
noteView = (TextView) findViewById(R.id.noteDisplay);
timeView = (TextView) findViewById(R.id.notetimeStampDisplay);
}
#Override
protected void onResume() {
super.onResume();
new MyTask().execute();
}
#Override
protected void onPause() {
super.onPause();
}