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我的應用程序能夠從GCM接收消息並將消息保存到手機上的SQLlite數據庫。這些消息可以在具有列表視圖的活動中查看。設備收到GCM IntentService消息時刷新ListView
在下面的代碼中，onPause（）函數刷新listView。這不是一個好的實現，因爲它只適用於在更新時不顯示活動。如果活動在更新時顯示，則列表是靜態的並且不會更新。
問題：
如何我更新列表視圖正在顯示活動時？或者有沒有辦法使用後臺服務來更新適配器，以便無論何時顯示活動，它總是顯示最新的數據。
是目前這種類型的功能目前不可能與android和我需要實現其他像'拉到刷新'的東西？在的onResume
刷新列表視圖（）崩潰的應用程序，並顯示了一個空指針異常。
活動：
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() {
}
}
中的代碼段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) {
}
}
}