observer-pattern | 易学教程

Mediator Vs Observer Object-Oriented Design Patterns

阅读更多关于 Mediator Vs Observer Object-Oriented Design Patterns

问题 I have been reading the Gang Of Four , in order to solve some of my problems and came across the Mediator pattern. I had earlier used Observer in my projects for making some GUI application. I am a bit confused as I do not find great difference between the two. I browsed to find the difference but could not find any apt answer for my query. Could some one help me to differentiate between the two with some good example which clearly demarcates the two? 回答1: The Observer pattern: Defines a one

Update: How to find event listeners on a DOM node in prototype?

阅读更多关于 Update: How to find event listeners on a DOM node in prototype?

问题 I'm looking for an updated answer to this question. It seems that Event.observers is no longer used (perhaps to avoid memory leaks) in Prototype 1.6+, so how do I track down now what event listeners are attached to an element? I know Firebug has a "break on next" button, but there are several mouse listeners on the body element that execute before I can get to the behavior that I want on another particular element, so is there some other way? 回答1: I've update the answer you linked to with

What is the opposite of the observer pattern?

阅读更多关于 What is the opposite of the observer pattern?

问题 As I understand it, the observer pattern allows for multiple observers to monitor a single subject. Is there a pattern for the opposite scenario? Is there a pattern for a single observer that monitors several subjects and responds when any one of them raises, say, a Notify event? 回答1: The Observer pattern can still be used: just have the same object register as an observer to many monitored objects. You'll probably want the "Notify" event to receive some kind of observed-object identifier

How to trigger function on value change?

阅读更多关于 How to trigger function on value change?

I realise this question has to do with event-handling and i've read about Python event-handler a dispatchers, so either it did not answer my question or i completely missed out the information. I want method m() of object A to be triggered whenever value v is changing: For instance (assuming money makes happy): global_wealth = 0 class Person() def __init__(self): self.wealth = 0 global global_wealth # here is where attribute should be # bound to changes in 'global_wealth' self.happiness = bind_to(global_wealth, how_happy) def how_happy(self, global_wealth): return self.wealth / global_wealth

Simple way of turning off observers during rake task?

阅读更多关于 Simple way of turning off observers during rake task?

问题 I'm using restful_authentication in my app. I'm creating a set of default users using a rake task, but every time I run the task an activation email is sent out because of the observer associated with my user model. I'm setting the activation fields when I create the users, so no activation is necessary. Anyone know of an easy way to bypass observers while running a rake task so that no emails get sent out when I save the user? Thanks. 回答1: You could add an accessor to your user model,

How do I create a Mailer Observer

阅读更多关于 How do I create a Mailer Observer

问题 I'd like to run some code whenever an email is sent on my app. As ActionMailer doesn't support after_filter, I would like to use an observer. The Rails docs mention this in passing, however does not elaborate. Thanks! 回答1: I'm surprised how little there is in Rails' documentation about this. Basically, ActionMailer in Rails 3 introduces the use of Interceptors (called before the message is sent) and Observers (after the message is sent). To set up an Observer, add the following to an

Pros and Cons of Listeners as WeakReferences

阅读更多关于 Pros and Cons of Listeners as WeakReferences

问题 What are the pros and cons of keeping listeners as WeakReferences. The big 'Pro' of course is that: Adding a listener as a WeakReference means the listener doesnt need to bother 'removing' itself. Update For those worried about the listener having the only reference to the object, why cant there be 2 methods, addListener() and addWeakRefListener()? those who dont care about removal can use the latter. 回答1: First of all, using WeakReference in listeners lists will give your object different

Observer is deprecated in Java 9. What should we use instead of it?

阅读更多关于 Observer is deprecated in Java 9. What should we use instead of it?

问题 Java 9 came out, and Observer has been deprecated. Why is that? Does it mean that we shouldn't implement observer pattern anymore? It would be good to know what is a better alternative? 回答1: Why is that? Does it mean that we shouldn't implement observer pattern anymore? Answering the latter part first - YES , it does mean you shouldn't implement Observer and Obervable s anymore. Why were they deprecated - They didn't provide a rich enough event model for applications. For example, they could

Python Observer Pattern: Examples, Tips? [closed]

阅读更多关于 Python Observer Pattern: Examples, Tips? [closed]

问题 Are there any exemplary examples of the GoF Observer implemented in Python? I have a bit code which currently has bits of debugging code laced through the key class (currently generating messages to stderr if a magic env is set). Additionally, the class has an interface for incrementally return results as well as storing them (in memory) for post processing. (The class itself is a job manager for concurrently executing commands on remote machines over ssh). Currently the usage of the class

Super-simple example of C# observer/observable with delegates

阅读更多关于 Super-simple example of C# observer/observable with delegates

I recently started digging into C# but I can't by my life figure out how delegates work when implementing the observer/observable pattern in the language. Could someone give me a super-simple example of how it is done? I have googled this, but all of the examples I found were either too problem-specific or too "bloated". The observer pattern is usually implemented with events . Here's an example: using System; class Observable { public event EventHandler SomethingHappened; public void DoSomething() => SomethingHappened?.Invoke(this, EventArgs.Empty); } class Observer { public void HandleEvent