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()
}
本文出自 “Programming in XMU” 博客，请务必保留此出处http://liuxp0827.blog.51cto.com/5013343/1356520