定义
命令模式将每个请求封装成一个对象，从而让用户使用不同的请求把客户端参数化；将请求进行排队或者记录请求日志，以及支持可撤销操作。
优点
行为请求和行为实现弱耦合，易扩展，修改，维护。
把请求一个操作的对象与知道怎么执行一个操作的对象分割开。
缺点
设计模式通病，大量衍生类的创建。
作用
它较容易地设计一个命令队列。
在需要情况下，可以较容易地将命令计入日志。
允许接收请求的一方决定是否要否决请求。
可以容易地实现对请求的撤销和重做。
由于加进新的具体命令类不影响其他的类，因此增加新的具体命令类很容易。
结构图
描述
去烧烤店吃烧烤，点烤鸡翅和羊肉串给厨房下命令。
完整示例
烧烤者
Class PHA.YX.Design.Command.Barbecuer Extends %RegisteredObject
{
Method BakeMutton()
{
w "烤羊肉串!",!
}
Method BakeChickenWing()
{
w "烤鸡翅!",!
}
}
抽象命令
Class PHA.YX.Design.Command.Command Extends %RegisteredObject
{
Property receiver As Barbecuer [ Private ];
Method %OnNew(receiver As Barbecuer) As %Status [ Private, ServerOnly = 1 ]
{
s ..receiver = receiver
Quit $$$OK
}
Method ExcuteCommand() [ Abstract ]
{
}
}
具体命令
Class PHA.YX.Design.Command.BakeMuttonCommand Extends Command
{
Method %OnNew(receiver As Barbecuer) As %Status [ Private, ServerOnly = 1 ]
{
dsuper(receiver)
Quit $$$OK
}
Method ExcuteCommand()
{
d ..receiver.BakeMutton()
}
}
Class PHA.YX.Design.Command.BakeChickenWingCommand Extends Command
{
Method %OnNew(receiver As Barbecuer) As %Status [ Private, ServerOnly = 1 ]
{
dsuper(receiver)
Quit $$$OK
}
Method ExcuteCommand()
{
d ..receiver.BakeChickenWing()
}
}
服务员
Class PHA.YX.Design.Command.Waiter Extends %RegisteredObject
{
Property orders As list Of Command [ Private ];
Method SetOrder(command As Command)
{
d ..orders.Insert(command)
w "增加订单" _ command.%ClassName() _ "时间" _ $zd($h,3) _ " " _ $zt($p($h, ",", "2"),1),!
}
Method CancelOrder(command As Command)
{
d ..orders.RemoveAt(command)
w "取消订单" _ command.%ClassName() _ "时间" _ $zd($h,3) _ " " _ $zt($p($h, ",", "2"),1),!
}
Method Notify()
{
f i = 1 : 1 : ..orders.Count() d
.d ..orders.GetAt(i).ExcuteCommand()
}
}
调用
/// dclass(PHA.YX.Design.Program).Command()
ClassMethod Command()
{
#dim boy as PHA.YX.Design.Command.Barbecuer
s boy =class(PHA.YX.Design.Command.Barbecuer).%New()
s bakeMuttonCommand1 =class(PHA.YX.Design.Command.BakeMuttonCommand).%New(boy)
s bakeMuttonCommand2 =class(PHA.YX.Design.Command.BakeMuttonCommand).%New(boy)
s bakeChickenWingCommand1 =class(PHA.YX.Design.Command.BakeChickenWingCommand).%New(boy)
#dim girl as PHA.YX.Design.Command.Waiter
s girl =class(PHA.YX.Design.Command.Waiter).%New()
d girl.SetOrder(bakeMuttonCommand1)
d girl.SetOrder(bakeMuttonCommand1)
d girl.CancelOrder(bakeMuttonCommand1)
d girl.SetOrder(bakeChickenWingCommand1)
d girl.Notify()
}
DHC-APP>dclass(PHA.YX.Design.Program).Command()
增加订单BakeMuttonCommand时间2020-04-07 09:43:56
增加订单BakeMuttonCommand时间2020-04-07 09:43:56
取消订单BakeMuttonCommand时间2020-04-07 09:43:56
增加订单BakeChickenWingCommand时间2020-04-07 09:43:56
烤羊肉串!
烤羊肉串!
烤鸡翅!
思考
电视机有 声音增大，减小，节目增加，减少，四个命令。客户端调用这四个命令。感兴趣的同学写完可以发我。