Mediator Pattern中介者模式
中介者模式
中介者模式(Mediator Pattern)是用来降低多个对象和类之间的通信复杂性。这种模式提供了一个中介类,该类通常处理不同类之间的通信,并支持松耦合,使代码易于维护。中介者模式属于行为型模式。
介绍
意图:用一个中介对象来封装一系列的对象交互,中介者使各对象不需要显式地相互引用,从而使其耦合松散,而且可以独立地改变它们之间的交互。
主要解决:对象与对象之间存在大量的关联关系,这样势必会导致系统的结构变得很复杂,同时若一个对象发生改变,我们也需要跟踪与之相关联的对象,同时做出相应的处理。
何时使用:多个类相互耦合,形成了网状结构。
如何解决:将上述网状结构分离为星型结构。
关键代码:对象 Colleague 之间的通信封装到一个类中单独处理。
应用实例: 1、中国加入 WTO 之前是各个国家相互贸易,结构复杂,现在是各个国家通过 WTO 来互相贸易。 2、机场调度系统。 3、MVC 框架,其中C(控制器)就是 M(模型)和 V(视图)的中介者。
优点: 1、降低了类的复杂度,将一对多转化成了一对一。 2、各个类之间的解耦。 3、符合迪米特原则。
缺点:中介者会庞大,变得复杂难以维护。
使用场景: 1、系统中对象之间存在比较复杂的引用关系,导致它们之间的依赖关系结构混乱而且难以复用该对象。 2、想通过一个中间类来封装多个类中的行为,而又不想生成太多的子类。
注意事项:不应当在职责混乱的时候使用。
Mediator Design Pattern
Rules of thumb 和其他几个设计模式的区别
- Chain of Responsibility, Command, Mediator, and Observer, address how you can decouple senders and receivers, but with different trade-offs. Chain of Responsibility passes a sender request along a chain of potential receivers. Command normally specifies a sender-receiver connection with a subclass. Mediator has senders and receivers reference each other indirectly. Observer defines a very decoupled interface that allows for multiple receivers to be configured at run-time.
- Mediator and Observer are competing patterns. The difference between them is that Observer distributes communication by introducing "observer" and "subject" objects, whereas a Mediator object encapsulates the communication between other objects. We've found it easier to make reusable Observers and Subjects than to make reusable Mediators.
- On the other hand, Mediator can leverage Observer for dynamically registering colleagues and communicating with them.
- Mediator is similar to Facade in that it abstracts functionality of existing classes. Mediator abstracts/centralizes arbitrary communication between colleague objects, it routinely "adds value", and it is known/referenced by the colleague objects (i.e. it defines a multidirectional protocol). In contrast, Facade defines a simpler interface to a subsystem, it doesn't add new functionality, and it is not known by the subsystem classes (i.e. it defines a unidirectional protocol where it makes requests of the subsystem classes but not vice versa).
Real-world code in C#
This real-world code demonstrates the Mediator pattern facilitating loosely coupled communication between different Participants registering with a Chatroom. The Chatroom is the central hub through which all communication takes place. At this point only one-to-one communication is implemented in the Chatroom, but would be trivial to change to one-to-many.
作者:Chuck Lu GitHub |
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