observer-pattern

There is a question already answered which is In C#, isn't the observer pattern already implemented using Events? It asks if the observer pattern is already implemented in c# using events. While I get the events and observer pattern, isn't the observer pattern really just delegates and events is a further implementation? You are correct. An event is simply a delegate with some slightly different functionality. All of the observer pattern can be implemented with delegates without ever touching the event keyword. You may be interested then, in what the "event" keyword actually brings to the

This problem is pretty common: an object should notify all its subscribers when some event occurs. In C++ we may use boost::signals or something else. But how to do this in Go language? It would be nice to see some working code example where a couple of objects are subscribed to a publisher and process notifications. Thanks This is actually pretty simple in Go. Use channels. This is the kind of thing they're made for. type Publish struct { listeners []chan *Msg } type Subscriber struct { Channel chan *Msg } func (p *Publisher) Sub(c chan *Msg) { p.appendListener(c) } func (p *Publisher) Pub(m

I am a senior level developer but I haven't had a lot of formal training and I although I have used many design patterns and seen them used in my years as a developer, no one really went out of their way to say. "Oh this is an observer pattern, or this is a Singleton pattern." Reading over some of the design patterns, I came across the Observer pattern and it seems to be to be very similar to the way the .NET framework events work. Am I missing something fundamental about this? The .NET Event model is pretty much a integrated implementation of the observer pattern in the common language

Let's say I want to implement an event bus using a OO programming language. I could do this (pseudocode): class EventBus listeners = [] public register(listener): listeners.add(listener) public unregister(listener): listeners.remove(listener) public fireEvent(event): for (listener in listeners): listener.on(event) This is actually the the observer pattern, but used for event-driven control flow of an application. How would you implement this pattern using a functional programming language (such as one of the lisp flavors)? I ask this because if one doesn't use objects, one would still need

I want to know about how to set our own Listeners in java.For example I have a function that increments number from 1 to 100. i want to set a listener when the value reaches 50. How can i do that? Pls suggest me any tutorial. Have a look at the source of any class that uses listeners. In fact it's quite easy: create an interface for your listener, e.g. MyListener maintain a list of MyListener upon each event that the listeners should listen to, iterate over the list and call the appropriate method with some event parameter(s) As for the observer pattern along with some Java code have a look at

I'd like to add an Auditor Observer which does an action anytime after_create for 3 models (books, characters, authors)... I recently heard of the Observer capability but can't find any documentation on the ability. Is it support in Rails 3? How do I create an Auditor Observer that does something after_create for 3 models? Thanks jpemberthy Rails observers are sweet, You can observe multiple models within a single observer First, you need to generate your observer: rails g observer Auditor Then, in your fresh auditor_observer.rb file define the models you wish to observe and then add the after

A C++ MVC framework I’m writing makes heavy use of the observer pattern. I have had a thorough read of the related chapter in Design Patterns (GoF, 1995) and had a look at a multitude of implementations in articles and existing libraries (including Boost). But as I was implementing the pattern, I could not help the feeling that there must be a better way - my client code involved lines and snippets that I felt should have been refactored into the pattern itself, if only I could find a way to overcome a few C++ limitations. Also, my syntax never appeared as elegant as that used in the ExtJs

I have an observer and I register an after_commit callback. How can I tell whether it was fired after create or update? I can tell an item was destroyed by asking item.destroyed? but #new_record? doesn't work since the item was saved. I was going to solve it by adding after_create / after_update and do something like @action = :create inside and check the @action at after_commit , but it seems that the observer instance is a singleton and I might just override a value before it gets to the after_commit . So I solved it in an uglier way, storing the action in a map based on the item.id on after

Hi I'm tyring to implement observer pattern in JavaScript: My index.js : $(document).ready(function () { var ironMan = new Movie(); ironMan.setTitle('IronMan'); ironMan.setRating('R'); ironMan.setId(1); // ironMan.setCast(['Robert Downey Jr.', 'Jeff Bridges', 'Gwyneth Paltrow']); var terminator = new Movie(); terminator.setTitle('Terminator'); terminator.setRating('P'); terminator.setId(2); console.log(ironMan.toString()); console.log(terminator.toString()); ironMan.play(); ironMan.stop(); ironMan.download(); ironMan.share('V. Rivas'); console.log(ironMan.getCast()[0]); }); My movie : var