在C#中如何正确实现命令设计模式？

Question

我正在研究设计模式,我目前正在研究命令模式.

这是我目前的代码:

// this is the receiver
class Calculator : IReceiver
{
    int x;
    int y;

    CommandOptions command;

    public Calculator(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    public void SetAction(CommandOptions command)
    {
        this.command = command;
    }

    public int GetResult()
    {
        int result = 0;

        switch(this.command)
        {
            case CommandOptions.ADD:
                result = this.x + this.y;
                break;

            case CommandOptions.SUBTRACT:
                result = this.x - this.y;
                break;

            case CommandOptions.MULTIPLY:
                result = this.x * this.y;
                break;
        }

        return result;
    }
}

// command
abstract class Command
{
    protected IReceiver receiver;

    public Command(IReceiver receiver)
    {
        this.receiver = receiver;
    }

    public abstract int Execute();
}

class AddCommand : Command
{
    public AddCommand(IReceiver receiver) : base(receiver)
    {
    }

    public override int Execute()
    {
        reciever.SetAction(CommandOptions.ADD);
        return receiver.GetResult();
    }
}

enum CommandOptions
{
    ADD,
    SUBTRACT,
    MULTIPLY
}

interface IReceiver
{
    void SetAction(CommandOptions command);
    int GetResult();
}


class Program
{
    static void Main(string[] args)
    {
        IReceiver receiver = new Calculator(500, 25);

        //#Issue:The SetAction() method of the receiver is accessible.
        //receiver.SetAction(CommandOptions.ADD);
        receiver.SetAction(CommandOptions.MULTIPLY);
        Command command = null;

        Console.Write("Enter option 1-3: ");

        int commandOption = int.Parse(Console.ReadLine());

        switch(commandOption)
        {
            case 1:
                command = new AddCommand(receiver);
                break;

            case 2:
                command = new SubtractCommand(receiver);
                break;

            case 3:
                command = new MultiplyCommand(receiver);
                break;

            default:
                command = new AddCommand(receiver);
                break;
        }

        Console.WriteLine(command.Execute());
        Console.ReadKey();
    }
}

请注意,在我的main方法中,我可以访问SetAction接收器的方法,该方法能够设置要使用的命令.

我的问题是:我的实现是否违反了命令模式的目的,并且我的实现是错误的,因为我能够在我的客户端代码中访问它？如果是这样,我该如何改进这种实现.

Answer 1

我拍了一些文本编辑(即没有运行它,期望语法错误:))你的代码.这是我如何模拟你的问题.

一些要点 -

1)让命令执行操作.在您的情况下,您有命令类,但计算器保存计算逻辑.而是将命令操作封装在命令类本身中

2)我已经把一个工厂把命令选项映射到命令,并通过删除breaks 保存了几行,因为我可以返回命令.

3)IReceiver现在保存传递给Command的值.在这种情况下,由于我们的运算符都是二进制的,我只使用了X和Y.对于其他情况,可以是数组或任何其他复杂类型.

4)除非你绝对需要,否则不需要枚举.

编辑 在重新审视时,我认为更好的解决方案是不使用命令注册接收器,而是在调用命令时传递参数.

//this is the receiver
class Calculator : IReceiver
{
    int y;
    int x;

    public Calculator(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    public int Calculate(int commandOption)
    {
        Command command = new CommandFactory().GetCommand(commandOption);
        return command.Execute(x , y);
    }

}


//command
interface ICommand
{    
    int Execute(int x, int y);
}

class AddCommand : Command
{
    public override int Execute(int x, int y)
    {
        return x + y;
    }
}

class MultiplyCommand : Command
{
    public override int Execute(int x, int y)
    {
        return x * y;
    }
}

class SubtractCommand : Command
{
    public override int Execute(int x, int y)
    {
        return x - y;
    }
}

interface IReceiver
{
    int X {get; set;}
    int Y {get; set;}
    int Calculate(int commandOption);
}

public class CommandFactory
{
    public GetCommand(int commandOption)
    {
        switch(commandOption)
        {
            case 1:
                return new AddCommand();
            case 2:
                return new SubtractCommand();
            case 3:
                return new MultiplyCommand();
            default:
                return new AddCommand();
        }       
    }
}

class Program
{
    static void Main(string[] args)
    {
        IReceiver receiver = new Calculator(500, 25);
        //#Issue:The SetAction() method of the receiver is accessible.
        //receiver.SetAction(CommandOptions.ADD);

        //Receiver no longer exposes SetAction
        //receiver.SetAction(CommandOptions.MULTIPLY);
        Console.Write("Enter option 1-3: ");
        int commandOption = int.Parse(Console.ReadLine());

        Console.WriteLine(receiver.Calculate(commandOption));
        Console.ReadKey();
    }
}