title: In what period does the firebase's app token changes and how to manage it?
body: <p>I am new to firebase I am learning it like a toddler learning to walk. So far I have managed to send a message to my own phone using a token generated for my phone by firebase framework. Now here's where it gets tricky (in my opinion). There is a method called <code>onTokenRefresh()</code> in the <code>FirebaseInstanceIdService</code> extended service. Since it is called <strong>refresh</strong>, Then I am assuming that it will change. I want to know when this token is created and when will it be changed?</p>
  
  <p>And if it changes, suppose I send a message to a device with token 'A' which is offline for now, so it will be queued. Now when the device gets online, it will "refresh" the token to 'B'. Now as the message was supposed to be delivered to token 'A', the message will never be delivered. How can I manage this situation?</p>