二十四种设计模式：命令模式(Command Pattern)

命令模式(Command Pattern)

介绍
将一个请求封装为一个对象，从而使你可用不同的请求对客户进行参数化；对请求排队或记录请求日志，以及支持可取消的操作。

示例
有一个Message实体类，某个类对它的操作有Insert()和Delete()方法。现在要求可以对之前的所有操作做撤销和重复。

　　MessageModel

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// Message实体类
    /// </summary>
    public class MessageModel
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="msg">Message内容</param>
        /// <param name="pt">Message发布时间</param>
        public MessageModel(string msg, DateTime pt)
        {
            this._message = msg;
            this._publishTime = pt;
        }

        private string _message;
        /// <summary>
        /// Message内容
        /// </summary>
        public string Message
        {
            get { return _message; }
            set { _message = value; }
        }

        private DateTime _publishTime;
        /// <summary>
        /// Message发布时间
        /// </summary>
        public DateTime PublishTime
        {
            get { return _publishTime; }
            set { _publishTime = value; }
        }
    }
}

　　Action

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// enum
    /// 定义操作的两种方法Insert和Delete
    /// </summary>
    public enum Action
    {
        /// <summary>
        /// Insert
        /// </summary>
        Insert,

        /// <summary>
        /// Delete
        /// </summary>
        Delete
    }
}

　　SqlMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// 接收者（Receiver）角色
    /// Sql方式操作Message
    /// </summary>
    public class SqlMessage
    {
        /// <summary>
        /// 操作
        /// </summary>
        /// <param name="action">操作的方法</param>
        /// <param name="mm">Message实体对象</param>
        public void Operation(Action action, MessageModel mm)
        {
            switch (action)
            {
                case Action.Insert : 
                    Insert(mm); 
                    break;
                case Action.Delete :
                    Delete(mm);
                    break;
            }
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        private void Insert(MessageModel mm)
        {
            // 代码略
        }

        /// <summary>
        /// 删除Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        private void Delete(MessageModel mm)
        {
            // 代码略
        }
    }
}

　　ICommand

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// 命令（Command）角色
    /// </summary>
    public interface ICommand
    {
        /// <summary>
        /// 执行
        /// </summary>
        /// <returns>操作的方法及操作的信息</returns>
        string Execute();

        /// <summary>
        /// 取消执行
        /// </summary>
        /// <returns>操作的方法及操作的信息</returns>
        string UnExecute();
    }
}

　　SqlMessageCommand

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// 具体命令（ConcreteCommand）角色
    /// </summary>
    public class SqlMessageCommand : ICommand
    {
        /// <summary>
        /// 操作的方法
        /// </summary>
        private Action _action;

        /// <summary>
        /// Message实体对象
        /// </summary>
        private MessageModel _mm;

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="action">操作的方法</param>
        /// <param name="mm">Message实体对象</param>
        public SqlMessageCommand(Action action, MessageModel mm)
        {
            this._action = action;
            this._mm = mm;
        }

        /// <summary>
        /// 执行
        /// </summary>
        /// <returns>操作的方法及操作的信息</returns>
        public string Execute()
        {
            new SqlMessage().Operation(_action, _mm);

            return _action.ToString() + "：" + _mm.Message;
        }

        /// <summary>
        /// 取消执行（调用一个方法，以决定取消执行的算法）
        /// </summary>
        /// <returns>操作的方法及操作的信息</returns>
        public string UnExecute()
        {
            _action = GetUndoAction(_action);
            new SqlMessage().Operation(_action, _mm);

            return _action.ToString() + "：" + _mm.Message;
        }

        /// <summary>
        /// 获得取消执行的算法
        /// </summary>
        /// <param name="action">操作的方法</param>
        /// <returns></returns>
        private Action GetUndoAction(Action action)
        {
            Action undo;

            switch (action)
            {
                case Action.Insert : 
                    undo = Action.Delete; 
                    break;
                case Action.Delete :
                    undo = Action.Insert;
                    break;
                // 这句没啥用
                default :
                    undo = Action.Insert;
                    break;
            }

            return undo;
        }
    }
}

　　Message

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Command
{
    /// <summary>
    /// 请求者（Invoker）角色
    /// </summary>
    public class Message
    {
        /// <summary>
        /// 命令集合（保存每次操作）
        /// </summary>
        private List<ICommand> _listCommand = new List<ICommand>();

        /// <summary>
        /// 命令集合中当前要执行的命令的索引
        /// </summary>
        private int current = 0;

        /// <summary>
        /// 执行Sql
        /// </summary>
        /// <param name="action">操作的方法</param>
        /// <param name="mm">Message实体对象</param>
        /// <returns>操作的方法及操作的信息</returns>
        public string Do(Action action, MessageModel mm)
        {
            string rtn = "";

            ICommand cmd = new SqlMessageCommand(action, mm);
            rtn = cmd.Execute();

            _listCommand.Add(cmd);
            current++;

            return rtn;
        }

        /// <summary>
        /// 撤销
        /// </summary>
        /// <param name="levels">执行撤销操作的次数</param>
        /// <returns>操作的方法及操作的信息（用空格分开多条记录）</returns>
        public string Undo(int levels)
        {
            string rtn = "";

            for (int i = 0; i < levels; i++)
            {
                if (current > 0)
                {
                    ICommand cmd = _listCommand[--current];
                    rtn += cmd.UnExecute() + " ";
                }
            }

            return rtn;
        }

        /// <summary>
        /// 重复
        /// </summary>
        /// <param name="levels">执行重复操作的次数</param>
        /// <returns>操作的方法及操作的信息（用空格分开多条记录）</returns>
        public string Redo(int levels)
        {
            string rtn = "";

            for (int i = 0; i < levels; i++)
            {
                if (current < _listCommand.Count - 1)
                {
                    ICommand cmd = _listCommand[current++];
                    rtn += cmd.UnExecute() + " ";
                }
            }

            return rtn;
        }
    }
}

　　Client

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Pattern.Command;

public partial class Command : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Message m = new Message();

        Response.Write("操作");
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第1条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第2条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第3条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第4条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Delete, new MessageModel("第2条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第5条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Delete, new MessageModel("第3条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第6条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(m.Do(Action.Insert, new MessageModel("第7条", DateTime.Now)));
        Response.Write("<br />");
        Response.Write("<br />");

        Response.Write("撤销4次操作");
        Response.Write("<br />");
        Response.Write(m.Undo(4));
        Response.Write("<br />");
        Response.Write("<br />");

        Response.Write("重复2次操作");
        Response.Write("<br />");
        Response.Write(m.Redo(2));
        Response.Write("<br />");
        Response.Write("<br />");

        Response.Write("撤销3次操作");
        Response.Write("<br />");
        Response.Write(m.Undo(3));
    }
}　

　　运行结果
　　操作
　　Insert：第1条
　　Insert：第2条
　　Insert：第3条
　　Insert：第4条
　　Delete：第2条
　　Insert：第5条
　　Delete：第3条
　　Insert：第6条
　　Insert：第7条

　　撤销4次操作
　　Delete：第7条 Delete：第6条 Insert：第3条 Delete：第5条

　　重复2次操作
　　Insert：第5条 Delete：第3条

　　撤销3次操作
　　Insert：第3条 Delete：第5条 Insert：第2条