A push notification is an important feature to engage users frequently, especially when the users are not using the app. Many people download an app, but only open it a few times. If you send them a push notification message, it will encourage them to open the app to get involved in a new activity. Implementing push notifications is very complex if you have to build everything from scratch; however, OneSignal makes it very simple. A push notification provider is a server that can communicate with the Apple Push Notification service (APNs), or Google's Firebase Cloud Messaging (FCM). You can set up your own provider server using existing open sources, but you have to maintain this server separately and keep up with potential changes from the APN APIs.

In this section, you will learn how to do the following things:

• Set up OneSignal for iOS push notification
• Configure an iOS app, certificates (app and push), and provisioning profile
• Write code to receive push notifications