64 lines
1.9 KiB
Text
64 lines
1.9 KiB
Text
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#lang scribble/manual
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@(require (for-label racket))
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@title{NotificationCenter}
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let an object emit notifications@section{related}
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Classes/SimpleController, Classes/NodeWatcher
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@section{categories}
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Control
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@section{description}
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One common OOP pattern is Model-View-Controller where one object (the controller) is a dependant of the model. Every time the model changes it notifies all of its dependants. In this case the model has a dictionary of dependants and iterates through those.
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Another common pattern is NotificationCenter wherein an object emits a notification and clients can register functions that will be executed when that notification happens.
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A link::Classes/Server:: emits a \newAllocators notification when it creates new node and bus allocators which it does when it quits or boots.
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@racketblock[
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NotificationCenter.notify(Server.default, \newAllocators);
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::
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You can listen for this:
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]
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@racketblock[
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NotificationCenter.register(Server.default, \newAllocators, yourself, {
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// throw away all your node variables
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// or stop the music
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});
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::
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The link::Classes/Buffer:: class register a function to clear its info cache whenever a server restarts. The server is emitting changed messages quite often (every 0.4 secs for the status updates), and the Buffer class is only interested in boot/quit events, so this is a more lightweight system for this purpose.
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]
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@section{ClassMethods}
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@section{private}
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initClass
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@section{method}
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notify
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The object emits a message and may also pass extra args.
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@section{method}
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register
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An interested client can register the action function for the object/message notification. A listener may only register one action per object/message notification.
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@section{method}
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unregister
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Remove the registrations.
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@section{method}
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registerOneShot
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After the notification has been emitted and handled, automatically unregister.
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@section{method}
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registrationExists
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Simply confirms if a registration is already in place.
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