问题
I have seen many questions on here and online that address this topic, but they all are from a long time ago, and are possibly outdated. I wanted to get a more recent answer if Firebase has implemented anything recently that is capable of a user to user push notification system, essentially what is used in all chat applications, or if the best option is still currently using Onesignal.
回答1:
Yes! These days, you can use Cloud Functions for Firebase to do things like send a notification when something interesting happens on the Database side of things.
Here's an example where a user gets notified via notifications when they gain a new follower. Obviously, your part of the database portion will probably change depending on what exactly you want to trigger a notification, but the general theory is the same.
来源：https://stackoverflow.com/questions/43790537/user-to-user-push-notifications