PHP - 什么是事件管理器？ [关闭]

Question

I have seen in a number of PHP frameworks the use of "event manager" classes. What exactly is an event manager within the scope of a "normal" MVC framework and what does it offer to the application in general?

Answer 1

First have a read about event driven programming to understand the basic idea.

I think every of the frameworks you've tagged has a manual page about the event system as well. At least CakePHP has a pretty detailed one about it's event system and it's event manager. The description of it is already half of an explanation what an event manager is:

The event manager is responsible for keeping track of event listeners, passing the correct data to them, and firing them in the correct order, when associated events are triggered. You can create multiple instances of this object to manage local events or keep a single instance and pass it around to manage all events in your app.

An event manager can attach listeners, or receivers, objects that listens or are "connected" to events. When an event is fired and dispatched by the event manager all listeners that are registered to one or more events will receive the event object instance and can work with it.

Be careful with events, correctly used they're great, inappropriate used they can make your application a hard to debug and hard to understand mess. Don't use them just because they're cool, document the events in your application.

Here is an example of how to inject additional fields into a form using the CakePHP event system. This use case might suit a CMS or if you have to conditionally add something to a form through a plugin system.