In what period does the firebase's app token changes and how to manage it?
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 onTokenRefresh() in the FirebaseInstanceIdService extended service. Since it is called refresh, Then I am assuming that it will change. I want to know when this token is created and when will it be changed?
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?
Answer
The token is generated, after the app is first launched, as soon as the phone can connect to the Google servers. Due to the required connectivity this might not happen immediately, but in most of the cases it will happen in few seconds after the user open the app.
As soon as the token is generated the method onTokenRefresh() is called.
As you pointed out the token can change, in which case the onTokenRefresh() method will be called again.
The refresh event is somehow rare, don't expect to see it often at all.
When the refresh token happens, all the messages that have been "successfully" sent (the API returned you a message-id) to the old token will be delivered.
Finally, even after the refresh happened the old token will still be working for a short period, to allow the app to communicate the new token to its back-end.