The provider/subscriber pattern defines a one-to-many, unidirectional flow of information from a provider object to any number of subscriber objects. The concept is that the provider has useful information or events that need to be communicated to other objects, its subscribers, which will use that information to perform additional actions or stay in synchronization with the provider. In Java parlance, the provider fires notifications to its listeners. In Objective-C terminology, the provider posts notifications to its observers.
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