How do iOS Push Notifications work?

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最佳答案

It was too much for me to put in a comment so.

From the documentation.

Apple Push Notification service (APNs) propagates push notifications to devices having applications registered to receive those notifications. Each device establishes an accredited and encrypted IP connection with the service and receives notifications over this persistent connection. Providers connect with APNs through a persistent and secure channel while monitoring incoming data intended for their client applications. When new data for an application arrives, the provider prepares and sends a notification through the channel to APNs, which pushes the notification to the target device..

I suggest reading the documentation for more information and how to use and configure. It's all there.

Push Notifications

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Device does not keep polling the server for the push notifications.

To keep it simple, consider an iPhone is connected to internet. On connecting to internet iPhone establishes connection to Apple Push Notifications server this connection is open connection which means data can be thrown to iPhone from server the moment data arrives to server.

Apple does not use HTTP protocol for Push notifications but if you understand HTTP Protocol its almost a similar methodology.

http://en.wikipedia.org/wiki/Push_technology#HTTP_server_push

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There is a really nice exaplanation of push notifications in this article.

In iOS, apps can’t do a lot in the background. Apps are only allowed to do limited set of activities so battery life is conserved.

But what if something interesting happens and you wish to let the user know about this, even if they’re not currently using your app?

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Each device can be updated with data using their own unique device tokens. This picture explains everything . .

enter image description here

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I created an infographic to explain the workflow of push notifications. Hope this is helpful.