Golang 设计模式 学习笔记（六）命令模式

由于最近一直在学习Golang，所以从本节起，所有设计模式学习笔记中的源码都由Golang来完成~

命令模式：将“请求”封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象。命令模式也支持可撤销的操作。

仔细看这个定义，我们知道一个命令对象通过在特定接收者(receiver)上绑定一组动作来封装一个请求。要达到这一点，命令对象将动作和接收者包进对象中。这个对象只暴露出一个execute()方法，当此方法被调用的时候，接收者就会进行这些动作。从外面看，其他对象不知道究竟哪个接收者进行了哪些动作，只知道如果调用了execute()，请求的目的就达到了。这些就实现了接收者和调用者的解耦合。

实现命令接口：

首先让所有的命令对象实现相同的包含一个方法的接口：

type command interface {
    execute()
}
                                                                                                    
//开灯命令
type lightOnCommand struct {
    mLight *light //命令对象包含的特定接收者
}
                                                                                                   
//返回一个开灯命令的实例对象
func NewLightOnCommand(light *light) command {
    return &lightOnCommand{mLight: light}
}
                                                                                                   
//实现接口方法捆绑接收者的动作
func (this *lightOnCommand) execute() {
    if !this.mLight.isOn() {
        this.mLight.setOn(true) //开灯
    }
}
                                                                                                   
//关灯命令
type lightOffCommand struct {
    mLight *light
}
          
func NewLightOffCommand(light *light) command {
    return &lightOffCommand{mLight: light}
}
                                                                                                   
func (this *lightOffCommand) execute() {
    if this.mLight.isOn() {
        this.mLight.setOn(false) //关灯
    }
}

我们应当考虑面向接口编程，大部分接收者都有简单的开关命令，故上述的代码可改为：

type receiver interface {
    setOn(bool) //true：开/false：关
    isOn() bool
}
                                 
//打开命令                                                 
type onCommand struct {
    receiver Receiver
}
                                                         
//创建打开命令的实例，为该实例捆绑接收者                          
func NewOnCommand(receiver Receiver) command {
    return &onCommand{receiver}
}
                                         
//被封装的“请求”                                          
func (this *onCommand) execute() {
    if !this.receiver.isOn() {
        this.receiver.setOn(true) //打开
    }
}
                                           
//关闭命令                                           
type offCommand struct {
    receiver Receiver
}
                                                                                      
func NewOffCommand(receiver Receiver) command {
    return &offCommand{receiver}
}
                                                                                      
func (this *offCommand) execute() {
    if !this.receiver.isOn() {
        this.receiver.setOn(false) //关闭
    }
}

最后，再来看看客户端的代码：

type RemoteController struct {
    slot command
}
                                                                 
func (this *RemoteController) SetCommand(command command) {
    this.slot = command
}
                                                                 
func (this *RemoteController) ButtonPressed() {
    if this.slot == nil {
        panic("Do not assign command to Controller's slot!")
    }
    this.slot.execute()
}

看看接收者们：

const (
    LIGHT = " light"
    DOOR  = " door"
)
                                  
//接收者接口        
type Receiver interface {
    setOn(bool)
    isOn() bool
}
                                             
type light struct {
    name string
    on   bool
}
                                             
func (this *light) setOn(b bool) {
    if b {
        fmt.Println(this.name + LIGHT + " is on.")
    } else {
        fmt.Println(this.name + LIGHT + " is off.")
    }
    this.on = b
}
                                             
func (this *light) isOn() bool {
    return this.on
}
                                             
func NewRoomLight() Receiver {
    return &light{"Room", false}
}
                                             
func NewTableLampLight() Receiver {
    return &light{"Table Lamp", false}
}
                                             
type door struct {
    name string
    on   bool
}
                                             
func (this *door) setOn(b bool) {
    if b {
        fmt.Println(this.name + DOOR + " is opened.")
    } else {
        fmt.Println(this.name + DOOR + " is closed.")
    }
    this.on = b
}
                                             
func (this *door) isOn() bool {
    return this.on
}
                                             
func NewGarageDoor() Receiver {
    return &door{"Garage", false}
}
                                             
func NewKitchenDoor() Receiver {
    return &door{"Kitchen", false}
}

来测试下吧~：

func main() {
        ctrl := new(command.RemoteController)
    var roomLight, garageDoor command.Receiver
              
    roomLight = command.NewRoomLight()
    garageDoor = command.NewGarageDoor()
              
    cmdOn := command.NewOnCommand(roomLight)
    cmdOff := command.NewOffCommand(garageDoor)
              
    ctrl.SetCommand(cmdOn)
    ctrl.ButtonPressed()
    ctrl.SetCommand(cmdOff)
    ctrl.ButtonPressed()
}

转载于:https://blog.51cto.com/liuxp0827/1356520