title: Customize firebase notification
body: <p>I have an Chat app in which a user is subscribed to an topic and each group is a topic. Whenever an message is sent in the group. An notification is sent to that topic. </p>
  
  <p>There are two problems that I am facing. </p>
  
  <ol>
  <li><p>When the sender sends the message in the group, a notification message is sent to the topic. But before the user gets the notification from firebase, He closes the application or the app goes in the background. So According to the firebase documentations, the notification is sent to the notification tray and not the onMessageReceived callback. </p></li>
  <li><p>The notification that is received from the firebase is added to the tray. How can the users other than the sender get the notification Id so that i can be cancelled when it required. How can this notification be customised?</p></li>
  </ol>
  
  <p>Is there a way to keep an active listener for receiving the notification when the app is in the background or terminated.</p>
  
  <p>Please help</p>