how do push notifications work

Push notifications are a key feature for keeping users updated with real-time information. At WWDC 2024, Apple introduced a new way to broadcast updates for live activities to a large audience with a single push notification. Here’s a summary of how push notifications work, particularly in the context of live activities:

1. Requesting a Push Token:

   • When a live activity is started, the app requests a push token from ActivityKit.
   • ActivityKit receives this push token from Apple Push Notification Service (APNs) and provides it to the app.
   • This push token is unique for each live activity requested by the app on the device.
   • The app then shares this unique push token with its app server.

2. Sending Updates:

   • When there is an update, the server sends a push notification to APNs with the token and the payload.
   • APNs delivers the payload to the respective device.
   • This method works well for use cases like tracking deliveries where each update is unique for every person.

3. Broadcast Push Notifications:

   • For scenarios where a large number of people are actively viewing updates for the same event (e.g., sports scores), broadcast push notifications are more efficient.
   • Each event is associated with a channel identified by a unique channel ID.
   • The app subscribes to updates on this channel, and the server sends a single push notification to APNs with the payload.
   • APNs then delivers this notification to all devices subscribed to the channel.

4. Channel Management:

   • Channels are used to manage broadcast push notifications.
   • The lifecycle of a channel and the live activity are independent. Even if there are no active subscribers, the channel ID remains valid.
   • The server should use the channel management API to remove old or unused channels when they are no longer needed.

5. Testing and Deployment:

   • The Push Notifications Console is a tool to test integration with broadcast notifications.
   • For production, the server should send requests for channel management and broadcast push notifications directly to APNs using the same authentication method (certificate or token-based).

For more detailed information, you can refer to the session Broadcast updates to your Live Activities (00:01:08).