九、外观模式

https://refactoringguru.cn/design-patterns/facade

如果有一个复杂的系统, 内部有很多子系统, 可以用 facade 封装一层, 只暴露出用户关心的简单接口.

注意: 随着需求增多, 不要做一个大而全的 facade, 而可以做多个小而美的 facade.

优点: 封装一层, 对外部用户屏蔽细节, 简化使用
缺点: 容易让所有系统, 都和 facade 耦合, 从而无法区分.

9.1 player

https://www.codingexplorations.com/blog/design-pattern-series-understanding-the-facade-design-pattern-in-go

播放电影, 需要各个子系统共同参与, 这种过程式的代码太繁琐, 可以抽象出 facade, 简化用户的操作

09facade/091player
├── player.go
├── player_test.go
└── readme.md

9.1.1 player_test.go

package _91playerimport "testing"/*
=== RUN   TestPlayMovie
开始播放电影...
Playing audio...
Playing video...
Showing screen...
结束播放电影...
--- PASS: TestPlayMovie (0.00s)
PASS
*/
func TestPlayMovie(t *testing.T) {f := &MultimediaFacade{audioPlayer:   &AudioPlayer{},videoPlayer:   &VideoPlayer{},screenManager: &ScreenManager{},}f.PlayMovie()
}

9.1.2 player.go

package _91playerimport ("fmt"
)// AudioPlayer 子系统
type AudioPlayer struct{}func (a *AudioPlayer) PlayAudio() {fmt.Println("Playing audio...")
}// VudioPlayer 子系统
type VideoPlayer struct{}func (v *VideoPlayer) PlayVideo() {fmt.Println("Playing video...")
}// ScreenManager 子系统
type ScreenManager struct{}func (s *ScreenManager) ShowScreen() {fmt.Println("Showing screen...")
}// MultimediaFacade 外观
type MultimediaFacade struct {audioPlayer   *AudioPlayervideoPlayer   *VideoPlayerscreenManager *ScreenManager
}func (f *MultimediaFacade) PlayMovie() {fmt.Println("开始播放电影...")f.audioPlayer.PlayAudio()f.videoPlayer.PlayVideo()f.screenManager.ShowScreen()fmt.Println("结束播放电影...")
}

9.2 login_register

网站都提供登录, 注册两种方式, 用户经常分不清楚

现在很多 APP 都提供了登录或注册功能, 即只需要输入手机号即可. 内部的逻辑是:

• 如果未注册, 则注册并登录
• 如果已注册, 则登录

可以提供一个 facade, 实现[登录或注册]的功能

09facade/092login_register
├── account.go
├── account_test.go
└── readme.md

9.2.1 account_test.go

package _92login_registerimport ("testing"
)/*
=== RUN   TestAccount
登录或注册
登录
--- PASS: TestAccount (0.00s)
PASS
*/
func TestAccount(t *testing.T) {a := &accountFacadeService{service: &accountService{}}a.loginOrRegister()
}

9.2.2 account.go

package _92login_registerimport "fmt"type iAccount interface {login()register()
}type iAccountFacade interface {loginOrRegister()
}type accountService struct{}func (s *accountService) login() {fmt.Println("登录")
}func (s *accountService) register() {fmt.Println("注册")
}// 是否已注册
func (s *accountService) isRegistered() bool {return true
}type accountFacadeService struct {service *accountService
}func (s *accountFacadeService) loginOrRegister() {fmt.Println("登录或注册")if !s.service.isRegistered() {s.service.register()}s.service.login()
}