乐在其中设计模式(C#) - 观察者模式(Observer Pattern)

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乐在其中设计模式(C#) - 观察者模式(Observer Pattern)

作者： webabcd


介绍
定义对象间的一种一对多的依赖关系,以便当一个对象的状态发生改变时,所有依赖于它的对象都得到通知并自动刷新。


示例
有一个Message实体类，某些对象对它的操作有Insert()方法，当发生某些改变的时候，通知所有这些对象并执行Insert()方法。

 

MessageModel

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

namespace Pattern.Observer
{
         /// <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; }
                }
        }
}

 

IMessage

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

namespace Pattern.Observer
{
         /// <summary>
         /// 操作Message的接口（Observer）
         /// </summary>
         public interface IMessage
        {
                 /// <summary>
                 /// 插入Message
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 /// <returns></returns>
                 string Insert(MessageModel mm);
        }
}

 

SqlMessage

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

namespace Pattern.Observer
{
         /// <summary>
         /// Sql方式操作Message（ConcreteObserver）
         /// </summary>
         public class SqlMessage : IMessage
        {
                 /// <summary>
                 /// 插入Message
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 /// <returns></returns>
                 public string Insert(MessageModel mm)
                {
                         return "sql方式：" + mm.Message + " " + mm.PublishTime.ToString();
                }    
        }
}

 

XmlMessage

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

namespace Pattern.Observer
{
         /// <summary>
         /// Xml方式操作Message（ConcreteObserver）
         /// </summary>
         public class XmlMessage : IMessage
        {
                 /// <summary>
                 /// 插入Message
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 /// <returns></returns>
                 public string Insert(MessageModel mm)
                {
                         return "xml方式：" + mm.Message + " " + mm.PublishTime.ToString();
                }    
        }
}

 

AbstractMessageSubject

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

namespace Pattern.Observer
{
         /// <summary>
         /// 抽象Message主题（Subject）
         /// </summary>
         public abstract class AbstractMessageSubject
        {
                 private MessageModel _messageModel;
                 private List<IMessage> list = new List<IMessage>();

                 /// <summary>
                 /// 构造函数
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 public AbstractMessageSubject(MessageModel mm)
                {
                         this._messageModel = mm;
                }

                 /// <summary>
                 /// 添加一个实现IMessage接口的对象
                 /// </summary>
                 /// <param name="m">实现IMessage接口的对象</param>
                 public void Attach(IMessage m)
                {
                        list.Add(m);
                }

                 /// <summary>
                 /// 移除一个实现IMessage接口的对象
                 /// </summary>
                 /// <param name="m">实现IMessage接口的对象</param>
                 public void Detach(IMessage m)
                {
                        list.Remove(m);
                }

                 /// <summary>
                 /// 通知所有观察者
                 /// </summary>
                 /// <returns></returns>
                 public string Notify()
                {
                         string s = "";
                         foreach (IMessage i in list)
                        {
                                s += i.Insert(_messageModel);
                                s += "<br />";
                        }

                         return s;
                }

                 /// <summary>
                 /// Message发布时间
                 /// </summary>
                 public DateTime PublishTime
                {
                        get { return _messageModel.PublishTime; }
                        set
                        {
                                _messageModel.PublishTime = value;
                                Notify();
                        }
                }
        }
}

 

MessageSubject

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

namespace Pattern.Observer
{
         /// <summary>
         /// Message主题（ConcreteSubject）
         /// </summary>
         public class MessageSubject : AbstractMessageSubject
        {
                 /// <summary>
                 /// 构造函数
                 /// </summary>
                 /// <param name="mm">Message实体对象</param>
                 public MessageSubject(MessageModel mm)
                        : base(mm)
                {
    
                }
        }
}

 

Test

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.Observer;

public partial class Observer : System.Web.UI.Page
{
         protected void Page_Load( object sender, EventArgs e)
        {
                MessageSubject m = new MessageSubject( new MessageModel( "插入Message", DateTime.Now));

                SqlMessage sqlMessage = new SqlMessage();
                XmlMessage xmlMessage = new XmlMessage();

                m.Attach(sqlMessage);
                m.Attach(xmlMessage);

                 // System.Threading.Thread.Sleep(1000);
                 // 修改了PublishTime就会通知所有观察者
                 // m.PublishTime = DateTime.Now;
                
                Response.Write(m.Notify());
        }
}

 

 

运行结果
sql方式：插入Message 2007-5-26 9:38:18
xml方式：插入Message 2007-5-26 9:38:18


参考
http://www.dofactory.com/Patterns/PatternObserver.aspx


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