用命令模式实现撤销与恢复 命令模式定义撤销与重做功能就此实现。整个过程中，最关键部分是命令对象的封装以及控制类与具体工厂类耦合的解除。

public class CeilingFan
{
     public const int HIGH = 2;
     public const int LOW = 1;
     public const int OFF = 0;
     int speed;

     public CeilingFan() { speed = OFF; }
     public void High() { speed = HIGH; }
     public void Low() { speed = LOW; }
     public int getSpeed() { return speed; }
}

public interface ICommand
{
    void execute();
    void undo();
}

// 高速运行类
public class CeilingFanHighCommand : ICommand
{
    CeilingFan ceilingFan; // 类中不用 new 方法创建类，降低耦合
    int preSpeed;  // 记录执行按键前的状态,便于回测
    public CeilingFanHighCommand(CeilingFan cf)
    {
        ceilingFan = cf;
    }

    public void execute()
    {
        preSpeed = ceilingFan.getSpeed();
        ceilingFan.High(); 
    }

    public void undo()
    {
        switch(preSpeed)
        {
            case CeilingFan.HIGH:
                ceilingFan.High();
                break;
            case CeilingFan.LOW:
                ceilingFan.Low();
                break;
            default:
                ceilingFan.Off();
                break;
        }
    }
}

// 低速运行类
public class CeilingFanLowCommand : ICommand
{
    CeilingFan ceilingFan; // 类中不用 new 方法创建类，降低耦合
    int preSpeed;  // 记录执行按键前的状态,便于回测
    public CeilingFanHighCommand(CeilingFan cf)
    {
        ceilingFan = cf;
    }

    public void execute()
    {
        preSpeed = ceilingFan.getSpeed();
        ceilingFan.Low(); 
    }

    public void undo()
    {
        switch(preSpeed)
        {
            case CeilingFan.HIGH:
                ceilingFan.High();
                break;
            case CeilingFan.LOW:
                ceilingFan.Low();
                break;
            default:
                ceilingFan.Off();
                break;
        }
    }
}

// 关闭类
public class CeilingFanLowCommand : ICommand
{
    CeilingFan ceilingFan; 
    int preSpeed;
    public CeilingFanHighCommand(CeilingFan cf)
    {
        ceilingFan = cf;
    }

    public void execute()
    {
        preSpeed = ceilingFan.getSpeed();
        ceilingFan.Off(); 
    }

    public void undo()
    {
        switch(preSpeed)
        {
            case CeilingFan.HIGH:
                ceilingFan.High();
                break;
            case CeilingFan.LOW:
                ceilingFan.Low();
                break;
            default:
                ceilingFan.Off();
                break;
        }
    }
}

public class Control
{
    List<ICommand> onCommands;
    Stack<ICommand> undoCommands;
    Stack<ICommand> redoCommands;  // 记录前一个命令, 便于 undo

    public Control()
    {
        onCommands = new List<ICommand>();
        undoCommands = new Stack<ICommand>();
        redoCommands = new Stack<ICommand>();
    }

    public void SetCommand(int slot, ICommand onCmd)
    {
        onCommands[slot] = onCmd;
    }

    public void OnButtonWasPressed(int slot)
    {
        if (onCommands[slot] != null)
        {
            onCommands[slot].execute();
            undoCommands.Push(onCommands[slot]);
        }
    }

    public void UndoButtonWasPressed() // 撤销,此处用 stack 后进先出的特性
    {
        if (undoCommands.Count > 0)
        {
            ICommand cmd = undoCommands.Pop();
            redoCommands.Push(cmd);
            cmd.undo();
        }
    }

    public void RedoButtonWasPressed()
    {
        if(redoCommands.Count > 0)
        {
            ICommand cmd = redoCommands.Pop();
            undoCommands.Push(cmd);
            cmd.execute();
        }
    }
}

// 测试类 （类途中的 RemoteLoader)
class Program
{
    static void Main(string[] args)
    {
        CeilingFan cf = new CeilingFan();
        CeilingFanHighCommand cfh = new CeilingFanHighCommand(cf);
        CeilingFanLowCommand cfl = new CeilingFanLowCommand(cf);

        Control ctr = new Control();
        // 假设 button0, button1 分别为高速低速
        ctr.SetCommand(0, cfh);
        ctr.SetCommand(1, cfl);

        ctr.OnButtonWasPressed(0);
        ctr.OnButtonWasPressed(1);
        ctr.UndoButtonWasPressed();
        ctr.RedoButtonWasPressed();
    }
}