I have published apps in playstore that use GCM and I have a plan to migrate using FCM. everything information i needed have found, but i have one question that not find answer yet. my question is when token have been created, are token will be change periodically like GCM does?
Similarly to how GCM works, the FCM token can change due to token-rotation.
You can intercept the token rotation implementing the callback:
Note: the token rotation is a rare-event. Don't expect to see it often.
But still, if you care about the token you should implement
onTokenRefresh() to be informed of changes.