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(Facade)模式示意性对象图(2)
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客户程序与抽象类的实现部分之间存在很大的依赖性,引入Facade将这个子系统与客户以及其他的子系统的分析,可以提供子系统的独立性和可移植性。构建一个层次结构的子系统时使用定义子系统中每层的入口点。如果子系统之间是相互依赖,你可以让它们仅通过进行通信,从而简化了它们之间的依赖关系。(3)
.NET架构中的外观模式(Facade)(4):
在这个架构中,总共分为四个逻辑层,分别为:用户层UI,业务外观层Business Façade,业务规则层Business Rule,数据访问层Data Access。其中Business Façade层的职责如下:
(1) 从“用户”层接收用户输入
(2) 如果请求需要对数据进行只读访问,则可能使用“数据访问”层
(3) 将请求传递到“业务规则”层
(4) 将响应从“业务规则”层返回到“用户”层
(5) 在对“业务规则”层的调用之间维护临时状态
Facade有助于建立层次结构的系统,实现了子系统与客户之间的松耦合关系,子系统内部的功能组件往往是紧耦合的。松耦合关系使得子系统的组件变化不会影响到它的客户。Facade消除了复杂的循环依赖关系。这一点在客户程序与子系统分别实现的时候格外重要。(3)
参考资料:
(1)《C# 设计模式》《 Desing Patterns in C#》(美)Steven John Metsker 著, 颜炯 译。
(2)http://www.j2medev.com/Article/Class3/pattern/200511/1020.html
(3)设计模式 可复用面向对象软件的基础 Design Patterns Elements of Reusable Object-Oriented Software 》(美)Erich Gamma Richard Helm Ralph Johnson John Vlissides 著,李英军 等译。
(4)http://www.cnblogs.com/Terrylee/archive/2006/03/17/352349.html
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