设计模式 - 策略、命令(3)

[b]1. 策略(Strategy) [/b]

购物时的付款方式：可采用现金也可用信用卡

策略模式：定义一系列算法，将各个算法封装起来，使算法可以相互替换。使算法独立于客户而变化。

方法：利用OO的多态性，动态绑定的特点

付款策略的实现：

using System;

//抽象的付款策略
abstract class PayMethod
{
abstract public void Pay();
}

//具体的付款策略 - 现金支付
class PayByCash : PayMethod
{
public override void Pay()
{
Console.WriteLine("Pay by cash!");
}
}

//具体的付款策略 - 信用卡支付
class PayByCreditCard : PayMethod
{
public override void Pay()
{
Console.WriteLine("Pay by credit card!");
}
}

//对策略进行设置和调用的上下文
class Context
{
private PayMethod paymethod;

//设置付款策略
public void SetPayMethod(PayMethod paymethod)
{
this.paymethod = paymethod;
}

//调用付款策略
public void Pay()
{
paymethod.Pay();
}
}

//策略模式的应用
public class Client
{
public static void Main(string[] args)
{
Context context = new Context();
context.SetPayMethod(new PayByCreditCard());
context.Pay();
//context.SetPayMethod(new PayByCash()); //此处体现了策略模式中，各策略的可替换性
//context.Pay();

Console.Read();
}
}

[b]2. 命令(Command) [/b]

命令模式：将请求封装成对象。。。。。

角色：抽象命令类，具体命令类，客户端，命令调用者，命令的接收者。

实例(总开关统一给电灯和风扇发出开或关的命令)：

using System;

//命令的接收者：风扇
class Fan
{
public void startRotate()
{
System.Console.WriteLine("Fan is rotating");
}
public void stopRotate()
{
System.Console.WriteLine("Fan is not rotating");
}
}

//命令的接收者：电灯
class Light
{
public void turnOn()
{
System.Console.WriteLine("Light is on ");
}
public void turnOff()
{
System.Console.WriteLine("Light is off");
}
}

//命令的调用者：总开关
class Switch
{
private Command UpCommand, DownCommand;
public Switch(Command Up, Command Down)
{
UpCommand = Up; // concrete Command registers itself with the invoker
DownCommand = Down;
}
public void flipUp()
{ // invoker calls back concrete Command, which executes the Command on the receiver
UpCommand.execute();

}
public void flipDown()
{
DownCommand.execute();
}
}

//具体命令：抽象的命令
public interface Command
{
void execute();
}

//具体命令：开灯命令
class LightOnCommand : Command
{
private Light myLight;
public LightOnCommand(Light L)
{
myLight = L;
}
public void execute()
{
myLight.turnOn();
}
}

//具体命令：关灯命令
class LightOffCommand : Command
{
private Light myLight;
public LightOffCommand(Light L)
{
myLight = L;
}
public void execute()
{
myLight.turnOff();
}
}

//具体命令：开风扇命令
class FanOnCommand : Command
{
private Fan myFan;
public FanOnCommand(Fan F)
{
myFan = F;
}
public void execute()
{
myFan.startRotate();
}
}

//具体命令：关风扇命令
class FanOffCommand : Command
{
private Fan myFan;

public FanOffCommand(Fan F)
{
myFan = F;
}
public void execute()
{
myFan.stopRotate();
}
}

//客户端
class CommandClient
{

static void Main(string[] args)
{
Light testLight = new Light();//创建命令的接收者 - 电灯

//创建用于电灯的各种具体命令
LightOnCommand testLOC = new LightOnCommand(testLight);
LightOffCommand testLFC = new LightOffCommand(testLight);

Switch testSwitch = new Switch(testLOC, testLFC);//创建命令的调用者 - 总开关
testSwitch.flipUp();
testSwitch.flipDown();

Fan testFan = new Fan();//创建命令的接收者 - 风扇

//创建用于风扇的各种具体命令
FanOnCommand foc = new FanOnCommand(testFan);
FanOffCommand ffc = new FanOffCommand(testFan);

Switch ts = new Switch(foc, ffc);//创建命令的调用者 - 总开关
ts.flipUp();
ts.flipDown();
}
}