title: android show notification with a popup on top of any application
body: <p>With the below code my notification are only added to the notification bar, no popup style message is displayed like if you would receive a whatsapp message when you're in another application. What makes that happen to a notification?</p>
  
  <pre><code>private void sendNotification(int distance, ViewObject viewObject) {
      Intent notificationIntent = new Intent(getApplicationContext(), MainActivity.class);
      notificationIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_SINGLE_TOP);
      notificationIntent.putExtra("path", viewObject.getPath());
      TaskStackBuilder stackBuilder = TaskStackBuilder.create(this);
      stackBuilder.addParentStack(MainActivity.class);
      stackBuilder.addNextIntent(notificationIntent);
      PendingIntent notificationPendingIntent = stackBuilder.getPendingIntent(Integer.parseInt(viewObject.getRefId()), PendingIntent.FLAG_UPDATE_CURRENT);
  
      NotificationCompat.BigTextStyle bigText = new NotificationCompat.BigTextStyle();
      bigText.bigText(String.format(getString(R.string.notification), viewObject.getTitle()));
      bigText.setBigContentTitle(getString(R.string.hello));
  
      NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
      builder.setSmallIcon(R.drawable.ic_wald_poi)
              .setLargeIcon(BitmapFactory.decodeResource(getResources(), R.drawable.ic_poi))
              .setColor(getResources().getColor(R.color.primary))
              .setContentTitle(getString(R.string.hello))
              .setContentIntent(notificationPendingIntent)
              .setContentText(String.format(getString(R.string.notification), viewObject.getTitle()))
              .setDefaults(Notification.DEFAULT_ALL)
              .setStyle(bigText);
  
      builder.setAutoCancel(true);
      NotificationManager mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
      mNotificationManager.notify(0, builder.build());
  }
  </code></pre>