Question

What are the key concepts that a developer should know when building an iPhone application that takes advantage of push notifications?

Answer 1

Number one most important thing, I think, is that your app can t depend on them. It s probably best to regard them as a nice thing for your user, rather than a part of your app s infrastructure. In particular:

Apple doesn t guarantee delivery of the notices. Yes, their infrastructure is pretty good, but there s no promise.
Only one alert can be up on the device at a time, and there s no log. So if the user has a bunch of push-enabled apps, you can t depend on them seeing your alerts.
The only way that your app knows about a notice is if the user chooses to run it in response to an alert.
The user can always turn push notices off, for your app, or for the whole device.

All of that also means: you can t cheat the "no background processes" restriction with the Push Notification Service. :-)

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