title: onNotificationPosted() method not called when the app is running in background
body: <p>I have written an app that reads notifications arriving to android device (API>=19) and used <strong>onNotificationPosted()</strong> method part of NotificationListenerService. I am able to read the posted notifications only if I keep the app active on the screen. Is there anyway I can keep the app <strong>running in the background</strong> and still use onNotificationsPosted method to retrieve the notification.</p>
  
  <p>Thanks!</p>