Dev:Notifications

A notification is a message sent to one or more observing objects to inform them of an event in a program. Not to be confused with notifications a user receives in the Notification Center or Push notifications.

Explain what they are, how to use them and why they are useful.

Relevant APIs:
 * NSNotificationCenter
 * NSDistributedNotificationCenter
 * CPDistributedNotificationCenter
 * CPDistributedMessagingCenter
 * CFNotificationCenter
 * notify

Darwin notifications are handled by Notifyd.

List of Notification pages
Here is a list of notification pages that have been linked to from this wiki.

This list is incomplete. You can help by expanding it. Or creating the listed pages. You can use Cycript and NotificationExplorer to retrieve the notifications that exist in a process.