Notification Notification for general use in any place

The best example can
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When sending to iphone tips by the need to use an external service messages, such as when you pick up a phone to call the phone number and the phone number came from and where tips.
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From application development, there are systems too Notification, as well as local, too. local was generally used within the program may notify mechanism was achieved. Similar to the observer pattern
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Thank you. . . Understand. . . observer pattern is valid