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→Scheduling Local Notifications
Suspended applications and those running in one of the three background execution modes do not, by definition, have access to the display of the iPhone device. In recognition of the fact that background applications may still need to display alert messages to users, Apple introduced the Local Notifications feature in iOS 4. Unlike the Push Notifications functionality available in previous versions of iOS, local notifications allow alerts to be triggered from within the local application without the need to rely on a remote server.
A local notification may be triggered at any time by an executing background application. Suspended applications must, however, schedule the notification to be delivered at a future time as part of the clean up process contained with the applicationDidEnterBackground method. A step-by-step example of how to schedule a local notification within an application entering suspended mode is covered in the chapter entitled [[Scheduling iOS 4 iPhone Local Notifications (Xcode4)|Scheduling iOS 4 iPhone Local Notifications]].
