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{    ///     /// Message实体类    /// 
    public class MessageModel    {        ///         /// 构造函数        /// 
        /// Message内容        /// Message发布时间        public MessageModel(string msg, DateTime pt)        {            this._message = msg;            this._publishTime = pt;        }        private string _message;        ///         /// Message内容        /// 
        public string Message        {            get { return _message; }            set { _message = value; }        }        private DateTime _publishTime;        ///         /// Message发布时间        /// 
        public DateTime PublishTime        {            get { return _publishTime; }            set { _publishTime = value; }        }    }}

　　Action

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Command{    ///     /// enum    /// 定义操作的两种方法Insert和Delete    /// 
    public enum Action    {        ///         /// Insert        /// 
        Insert,        ///         /// Delete        /// 
        Delete    }}

　　SqlMessage

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Command{    ///     /// 接收者（Receiver）角色    /// Sql方式操作Message    /// 
    public class SqlMessage    {        ///         /// 操作        /// 
        /// 操作的方法        /// Message实体对象        public void Operation(Action action, MessageModel mm)        {            switch (action)            {                case Action.Insert :                     Insert(mm);                     break;                case Action.Delete :                    Delete(mm);                    break;            }        }        ///         /// 插入Message        /// 
        /// Message实体对象        private void Insert(MessageModel mm)        {            // 代码略        }        ///         /// 删除Message        /// 
        /// Message实体对象        private void Delete(MessageModel mm)        {            // 代码略        }    }}

　　ICommand

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Command{    ///     /// 命令（Command）角色    /// 
    public interface ICommand    {        ///         /// 执行        /// 
        /// 
     
      操作的方法及操作的信息
             string Execute();        ///         /// 取消执行        /// 
        /// 
     
      操作的方法及操作的信息
             string UnExecute();    }}

　　SqlMessageCommand

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Command{    ///     /// 具体命令（ConcreteCommand）角色    /// 
    public class SqlMessageCommand : ICommand    {        ///         /// 操作的方法        /// 
        private Action _action;        ///         /// Message实体对象        /// 
        private MessageModel _mm;        ///         /// 构造函数        /// 
        /// 操作的方法        /// Message实体对象        public SqlMessageCommand(Action action, MessageModel mm)        {            this._action = action;            this._mm = mm;        }        ///         /// 执行        /// 
        /// 
     
      操作的方法及操作的信息
             public string Execute()        {            new SqlMessage().Operation(_action, _mm);            return _action.ToString() + "：" + _mm.Message;        }        ///         /// 取消执行（调用一个方法，以决定取消执行的算法）        /// 
        /// 
     
      操作的方法及操作的信息
             public string UnExecute()        {            _action = GetUndoAction(_action);            new SqlMessage().Operation(_action, _mm);            return _action.ToString() + "：" + _mm.Message;        }        ///         /// 获得取消执行的算法        /// 
        /// 操作的方法        /// 
             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{    ///     /// 请求者（Invoker）角色    /// 
    public class Message    {        ///         /// 命令集合（保存每次操作）        /// 
        private List
     
       _listCommand = new List
      
       ();        /// 
               /// 命令集合中当前要执行的命令的索引        /// 
        private int current = 0;        /// 
               /// 执行Sql        /// 
        /// 
       操作的方法        /// 
       Message实体对象        /// 
       
        操作的方法及操作的信息
               public string Do(Action action, MessageModel mm)        {            string rtn = "";            ICommand cmd = new SqlMessageCommand(action, mm);            rtn = cmd.Execute();            _listCommand.Add(cmd);            current++;            return rtn;        }        /// 
               /// 撤销        /// 
        /// 
       执行撤销操作的次数        /// 
       
        操作的方法及操作的信息（用空格分开多条记录）
               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;        }        /// 
               /// 重复        /// 
        /// 
       执行重复操作的次数        /// 
       
        操作的方法及操作的信息（用空格分开多条记录）
               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("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第1条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第2条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第3条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第4条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Delete, new MessageModel("第2条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第5条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Delete, new MessageModel("第3条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第6条", DateTime.Now)));        Response.Write("
");        Response.Write(m.Do(Action.Insert, new MessageModel("第7条", DateTime.Now)));        Response.Write("
");        Response.Write("
");        Response.Write("撤销4次操作");        Response.Write("
");        Response.Write(m.Undo(4));        Response.Write("
");        Response.Write("
");        Response.Write("重复2次操作");        Response.Write("
");        Response.Write(m.Redo(2));        Response.Write("
");        Response.Write("
");        Response.Write("撤销3次操作");        Response.Write("
");        Response.Write(m.Undo(3));    }}