Head First 设计模式之命令模式（CommandPattern）

Posted 2020-08-23 星星之火

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前言：

本章会将封装带入到一个全新的境界，把方法调用封装起来。通过封装方法调用，把运算块包装成形。调用此运算的对象不需要知道事情是如何进行的，只要知道如何使用包装形成的方法来完成它就ok了。

1 现实场景应用

现在有一个遥控器，该遥控器有7个插槽需要编程，可以在每个插槽上放上不同的装置，然后用按钮控制它，这七个插槽具备各自的“开”“关”按钮，还有一个整体用的撤销按钮，会撤销最后一个按钮的动作。

1.1 创建第一个命令对象

1.1.1 定义命令接口

public interfaceCommand
    {
        void Execute();
    }

1.1.2 实现一个打开灯的命令

publicclass Light //电灯类
    {
        public void On()
        {
            System.Console.WriteLine("Light  is On !");
        }
        public void Off()
        {
            System.Console.WriteLine("Light is Off !");
        }
}
    public class LightOnCommand : Command//实现开灯命令
    {
        private Light light;
        public LightOnCommand(Light light)
        {
            this.light = light;
        }
        public void Execute()
        {
            light.On();
        }      
    }

1.1.3 使用命令对象

public class LightControl
    {
        privateCommand soft;
        publicvoid SetCommand(Command cmd)
        {
            soft= cmd;//设置命令对象
        }
        publicvoid ButtonWasPressed()
        {
           soft.Execute();//调用命令对象的方法
        }
}

1.1.4 简单测试

LightControl lightControl = new LightControl();//模拟命令的调用者
Lightlight = new Light();//创建一个电灯对象，作为命令的接收者
LightOnCommand lightOnCommand = new LightOnCommand(light);//创建一个命令，并将接受者传递给它
lightControl.SetCommand(lightOnCommand);//将命令传给调用者
lightControl.ButtonWasPressed();//模拟触发按钮

1.2 实现遥控器

public class RemoteControl
    {
        Command[] onCommands;//定义打开的命令数组
        Command[] offCommands; //定义关闭的命令数组
        public RemoteControl()
        {
            onCommands = new Command[7];
            offCommands = new Command[7];
            Command noCommand = newNoCommand();
            for (int i = 0; i < 7; i++)
            {
                onCommands[i] = noCommand;//初始化命令数组（默认设置为无命令）
                offCommands[i] = noCommand;
            }
        }
        //将命令设置到对应的控制器
        public void SetCommand(int index,Command onCommand, Command offCommand)
        {
            onCommands[index] = onCommand;
            offCommands[index] = offCommand;
        }
        //触发打开控制器
        public void OnButtonWasPressed(int index)
        {
            onCommands[index].Execute();
        }
        //触发关闭控制器
        public void OffButtonWasPressed(intindex)
        {
            offCommands[index].Execute();
        }
        public override string ToString()
        {
            StringBuilder str = newStringBuilder();
            str.Append("\n------RemoteControl ------\n");
            for (int i = 0; i <onCommands.Length; i++)
            {
                str.Append("[solt" +i + "]" + onCommands[i].GetType().FullName + "      " +offCommands[i].GetType().FullName + "\n");
            }
            return str.ToString();
        }
    }

1.3 实现其他控制器

 //关闭电灯命令
   public classLightOffCommand : Command
    {
        privateLight light;
        publicLightOffCommand(Light light)
        {
           this.light = light;
        }
        publicvoid Execute()
        {
           light.Off();
        }
        publicvoid Undo()
        {
           light.On();
        }
}
//打开电扇命令
public class CeilingFanOnCommand : Command
    {
       CeilingFan ceilingFan;
        intpreSpeed;
        publicCeilingFanOnCommand(CeilingFan ceilingFan)
        {
           this.ceilingFan = ceilingFan;
        }
        publicvoid Execute()
        {
           ceilingFan.On();
        }
        publicvoid Undo()
        {
           ceilingFan.Off();
        }
    }
 //关闭电扇命令
    public classCeilingFanOffCommand : Command
    {
       CeilingFan ceilingFan;
        publicCeilingFanOffCommand(CeilingFan ceilingFan)
        {
           this.ceilingFan = ceilingFan;
        }
        publicvoid Execute()
        {
           ceilingFan.Off();
        }
        publicvoid Undo()
        {
           ceilingFan.On();
        }
    }
//打开车库门命令
    public classGarageDoorOnCommand : Command
    {
       GarageDoor garageDoor;
        publicGarageDoorOnCommand(GarageDoor garageDoor)
        {
            this.garageDoor= garageDoor;
        }
        publicvoid Execute()
        {
           garageDoor.On();
        }
        publicvoid Undo()
        {
           garageDoor.Off();
        }
    }
//关闭车库门命令
    public classGarageDoorOffCommand : Command
    {
       GarageDoor garageDoor;
        publicGarageDoorOffCommand(GarageDoor garageDoor)
        {
           this.garageDoor = garageDoor;
        }
        publicvoid Execute()
        {
            garageDoor.Off();
        }
        publicvoid Undo()
        {
           garageDoor.On();
        }
    }
//打开CD命令
    public classStereCDOnCommand : Command
    {
        StereCDstereCD;
        publicStereCDOnCommand(StereCD stereCD)
        {
           this.stereCD = stereCD;
        }
 
        publicvoid Execute()
        {
           stereCD.On();
        }
        publicvoid Undo()
        {
           stereCD.Off();
        }
    }
//关闭CD命令
    public classStereCDOffCommand : Command
    {
        StereCDstereCD;
        publicStereCDOffCommand(StereCD stereCD)
        {
           this.stereCD = stereCD;
        }
        publicvoid Execute()
        {
           stereCD.Off();
        }
        publicvoid Undo()
        {
           stereCD.On();
        }
    }

1.4简单测试

RemoteControlremoteControl = new RemoteControl ();
            CeilingFan ceilingFan = newCeilingFan("Living Room");//创建电扇对象
            GarageDoor garageDoor = newGarageDoor();//创建车库门对象
            StereCD stereCD = new StereCD();//创建CD对象
Light light = new Light();//创建电灯对象
            LightOnCommand lightOnCommand = newLightOnCommand(light);//创建开灯命令
            LightOffCommand lightOffCommand =new LightOffCommand(light); //创建关灯命令
CeilingFanOnCommandceilingFanOn = new CeilingFanOnCommand(ceilingFan); //创建开电扇命令
            CeilingFanOffCommand ceilingFanOff= new CeilingFanOffCommand(ceilingFan);//创建关电扇命令
            GarageDoorOnCommand garageDoorOn =new GarageDoorOnCommand(garageDoor);//创建打开电扇命令
            GarageDoorOffCommand garageDoorOff= new GarageDoorOffCommand(garageDoor);//创建关闭电扇命令
            StereCDOnCommand stereCDOn = newStereCDOnCommand(stereCD);//创建打开CD命令
            StereCDOffCommand stereCDOff = newStereCDOffCommand(stereCD);//创建关闭CD命令
            remoteControl.SetCommand(0,lightOnCommand, lightOffCommand);//将电灯命令设置到对应的控制器上
            remoteControl.SetCommand(1,ceilingFanOn, ceilingFanOff); //将电灯命令设置到对应的控制器上
            remoteControl.SetCommand(2,garageDoorOn, garageDoorOff); //将车库门命令设置到对应的控制器上
            remoteControl.SetCommand(3,stereCDOn, stereCDOff); //将CD命令设置到对应的控制器上
  remoteControl.OnButtonWasPressed(0);
           remoteControl.OffButtonWasPressed(0);
           remoteControl.OnButtonWasPressed(1);
           remoteControl.OffButtonWasPressed(1);
           remoteControl.OnButtonWasPressed(2);
           remoteControl.OffButtonWasPressed(2);
           remoteControl.OnButtonWasPressed(3);
           remoteControl.OffButtonWasPressed(3);

1.5 实现撤销命令

1.5.1 修改命令接口，新增Undo（）方法

public interfaceCommand
    {
        void Execute();
        void Undo();//新增撤销方法
}

1.5.2 修改命令，实现Undo方法

public class LightOnCommand : Command
    {
        private Light light;
        public LightOnCommand(Light light)
        {
            this.light = light;
        }
        public void Execute()
        {
            light.On();
        }
        public void Undo()//实现Undo方法
        {
            light.Off(); 
        }
}

其他类都依次修改

1.5.3 修改RemoteControl类，新增Command对象记录上一步操作

public class RemoteControlWithUndo
    {
       Command[] onCommands;
       Command[] offCommands;
        CommandundoCommand;//创建Command对象用来记录上一步执行的命令
        publicRemoteControlWithUndo()
        {
           onCommands = new Command[7];
           offCommands = new Command[7];
           Command noCommand = new NoCommand();
            for(int i = 0; i < 7; i++)
            {
               onCommands[i] = noCommand;
               offCommands[i] = noCommand;
            }
           undoCommand = noCommand;
        }
………
……..
        publicvoid OnButtonWasPressed(int index)
        {
           onCommands[index].Execute();
           undoCommand = onCommands[index];//记录打开命令
        }
        publicvoid OffButtonWasPressed(int index)
        {
           offCommands[index].Execute();
           undoCommand = offCommands[index];//记录关闭命令
        }
        publicvoid UndoButtonWasPressed()//执行撤销
        {
           undoCommand.Undo();
        }
       ……
       ……       
    }

1.6 宏命令

让遥控器具有Party模式，即一个按键能够同步调用多个命令，这就是所谓的宏命令。

 public class MacroCommand : Command
    {
        Command[] commands;//定义命令数组，用来接收传入的命令
        public MacroCommand(Command[] commands)
        {
            this.commands = commands;
        }
        public void Execute()//批量处理多个命令（即初始化的时候传入的命令数组）
        {
            for (int i = 0; i <commands.Length; i++)
                commands[i].Execute();
        }
        public void Undo()
        {
            for (int i = 0; i <commands.Length; i++)
                commands[i].Undo();
        }
    }