深入浅出设计模式-008：外观模式(Facade Pattern)

深入浅出设计模式-008：外观模式(Facade Pattern)

一：将一个或数个类的复杂的一切都隐藏在背后，只显露出一个干净美好的外观    外观没有“封装”子系统的类，外观只是提供简化的接口。所以客户如果觉得有必要，依然可以直接使用子系统类。即提供简化接口的同时，依然将系统完整的功能暴露出来，以供需要的人使用。    外观不仅是简化了接口，也将客户从组件的子系统中解耦。    外观和适配器可以包装许多类，但是外观的意图是简化接口，而适配器的意图是将接口转换成不同的接口。    二：外观模式：提供一个统一的接口，用来访问子系统中的一群接口。外观定义了一个高层接口，让子系统更容易使用。

三：设计原则：最少只是：减少对象之间的交互，只留下几个“密友”。即只和你的密友谈话。    这个原则希望我们在设计中，不要让太多的类耦合在一起，免得修改系统中的一部分，会影响到其他的部分。    如果系统类之间相互依赖，那么这个系统就会变成一个易碎的系统，它需要花许多成本维护，也会因为太复杂而不容易被其他人了解。

四：当需要使用一个现有的类而其接口并不符合你的需要时，就使用适配器。    当需要简化并统一一个很大的接口或者一群复杂的接口时，使用外观。    适配器改变接口以符合客户的期望。    外观将客户从一个复杂的子系统中解耦。    实现一个适配器可能需要一番功夫，也可能不费功夫，视目标接口的大小与复杂度而定。    实现一个外观，需要将子系组合进外观中，然后将工作委托给子系统执行。    适配器模式的两种形式：对象适配器和类适配器。类适配器需要用到多重继承。    你可以为一个子系统实现一个以上的外观。    适配器将一个对象包装起来以改变其接口。装饰者将一个对象包装起来以增加新的行为和责任，而外观将一群对象包装起来以简化接口

五：如组合音响，不用一步步的操作来完成，可以封装成一个按钮。    public class Amplifier {     Tuner tuner;     DvdPlayer dvd;     CdPlayer cd;    } public class Tuner { } public class DvdPlayer {  Amplifier amplifier;    } public class CdPlayer {  Amplifier amplifier;    } public class Projector {  DvdPlayer dvdPlayer;    } public class TheaterLights {} public class Screen {} public class PopcornPopper {} public class HomeTheaterFacade {  Amplifier amp;   Tuner tuner;  DvdPlayer dvd;  CdPlayer cd;  Projector projector;  TheaterLights lights;  Screen screen;  PopcornPopper popper;   public HomeTheaterFacade(Amplifier amp,    Tuner tuner,    DvdPlayer dvd,    CdPlayer cd,    Projector projector,    Screen screen,   TheaterLights lights,   PopcornPopper popper) {   this.amp = amp;   this.tuner = tuner;   this.dvd = dvd;   this.cd = cd;   this.projector = projector;   this.screen = screen;   this.lights = lights;   this.popper = popper;  }

        //将看电影前的一序列复杂动作封装成一个简化的接口  public object WatchMovie(string movie) {   StringBuilder watchMovieString = new StringBuilder();

   watchMovieString.Append("Get ready to watch a movie.../n");   watchMovieString.Append(popper.On());//打开爆米花机   watchMovieString.Append(popper.Pop());//开始爆米花   watchMovieString.Append(lights.Dim(10));//灯光调暗到10%   watchMovieString.Append(screen.Down());//把屏幕放下   watchMovieString.Append(projector.On());//打开投影机   watchMovieString.Append(projector.WideScreenMode());//将投影机设置到屏幕模式   watchMovieString.Append(amp.On());//打开功放   watchMovieString.Append(amp.SetDvd(dvd));//是指DVD   watchMovieString.Append(amp.SetSurroundSound());//设置成环绕立体模式   watchMovieString.Append(amp.SetVolume(5));//音量调到5   watchMovieString.Append(dvd.On());//打开DVD   watchMovieString.Append(dvd.Play(movie));//终于可以看电影了

   return watchMovieString.ToString();  }   public object EndMovie() {   StringBuilder endMovieString = new StringBuilder();

   endMovieString.Append("Shutting movie theater down.../n");   endMovieString.Append(popper.Off());   endMovieString.Append(lights.On());   endMovieString.Append(screen.Up());   endMovieString.Append(projector.Off());   endMovieString.Append(amp.Off());   endMovieString.Append(dvd.Stop());   endMovieString.Append(dvd.Eject());   endMovieString.Append(dvd.Off());

   return endMovieString.ToString();  }

  public object ListenToCd(string cdTitle) {   StringBuilder listenToCdString = new StringBuilder();

   listenToCdString.Append("Get ready for an audio experence.../n");   listenToCdString.Append(lights.On());   listenToCdString.Append(amp.On());   listenToCdString.Append(amp.SetVolume(5));   listenToCdString.Append(amp.SetCd(cd));   listenToCdString.Append(amp.SetStereoSound());   listenToCdString.Append(cd.On());   listenToCdString.Append(cd.Play(cdTitle));

   return listenToCdString.ToString();  }

  public object EndCd() {   StringBuilder endCdString = new StringBuilder();

   endCdString.Append("Shutting down CD.../n");   endCdString.Append(amp.Off());   endCdString.Append(amp.SetCd(cd));   endCdString.Append(cd.Eject());   endCdString.Append(cd.Off());

   return endCdString.ToString();  }

  public object ListenToRadio(double frequency) {   StringBuilder listenToRadioString = new StringBuilder();

   listenToRadioString.Append("Tuning in the airwaves.../n");   listenToRadioString.Append(tuner.On());   listenToRadioString.Append(tuner.SetFrequency(frequency));   listenToRadioString.Append(amp.On());   listenToRadioString.Append(amp.SetVolume(5));   listenToRadioString.Append(amp.SetTuner(tuner));

   return listenToRadioString.ToString();  }

  public object EndRadio() {   StringBuilder endRadioString = new StringBuilder();

   endRadioString.Append("Shutting down the tuner.../n");   endRadioString.Append(tuner.Off());   endRadioString.Append(amp.Off());

   return endRadioString.ToString();  } }

    static void Main(string[] args)    {        Amplifier amp = new Amplifier("Top-O-Line Amplifier");        Tuner tuner = new Tuner("Top-O-Line Tuner", amp);        DvdPlayer dvd = new DvdPlayer("Top-O-Line DVD Player", amp);        CdPlayer cd = new CdPlayer("Top-O-Line CD Player", amp);        Projector Projector projector = new Projector("Top-O-Line Projector", dvd);        TheaterLights lights = new TheaterLights("Theater Ceiling Lights");        Screen screen = new Screen("Theater Screen");        PopcornPopper popper = new PopcornPopper("Popcorn Popper");        HomeTheaterFacade homeTheater = new HomeTheaterFacade(amp, tuner, dvd, cd, projector, screen, lights, popper);

        homeTheater.WatchMovie("Toy Story");        homeTheater.EndMovie();

        homeTheater.ListenToCd("Dark Side of the Moon");        homeTheater.EndCd();

        homeTheater.ListenToRadio(92.5);        homeTheater.EndRadio();    }