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