樂在其中設計模式(C#) - 觀察者模式(Observer Pattern)

樂在其中設計模式(C#) - 觀察者模式(Observer Pattern)

介紹

定義對象間的一種一對多的依賴關系,以便當一個對象的狀态發生改變時,所有依賴于它的對象都得到通知并自動重新整理。

示例

有一個Message實體類，某些對象對它的操作有Insert()方法，當發生某些改變的時候，通知所有這些對象并執行Insert()方法。

MessageModel

using System; 

using System.Collections.Generic; 

using System.Text; 

namespace Pattern.Observer 

{ 

        /// <summary> 

        /// Message實體類 

        /// </summary> 

        public class MessageModel 

        { 

                /// <summary> 

                /// 構造函數 

                /// </summary> 

                /// <param name="msg">Message内容</param> 

                /// <param name="pt">Message釋出時間</param> 

                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釋出時間 

                public DateTime PublishTime 

                        get { return _publishTime; } 

                        set { _publishTime = value; } 

        } 

}

IMessage

        /// 操作Message的接口（Observer） 

        public interface IMessage 

                /// 插入Message 

                /// <param name="mm">Message實體對象</param> 

                /// <returns></returns> 

                string Insert(MessageModel mm); 

SqlMessage

        /// Sql方式操作Message（ConcreteObserver） 

        public class SqlMessage : IMessage 

                public string Insert(MessageModel mm) 

                        return "sql方式：" + mm.Message + " " + mm.PublishTime.ToString(); 

                }    

XmlMessage

        /// Xml方式操作Message（ConcreteObserver） 

        public class XmlMessage : IMessage 

                        return "xml方式：" + mm.Message + " " + mm.PublishTime.ToString(); 

AbstractMessageSubject

        /// 抽象Message主題（Subject） 

        public abstract class AbstractMessageSubject 

                private MessageModel _messageModel; 

                private List<IMessage> list = new List<IMessage>(); 

                public AbstractMessageSubject(MessageModel mm) 

                        this._messageModel = mm; 

                /// 添加一個實作IMessage接口的對象 

                /// <param name="m">實作IMessage接口的對象</param> 

                public void Attach(IMessage m) 

                        list.Add(m); 

                /// 移除一個實作IMessage接口的對象 

                public void Detach(IMessage m) 

                        list.Remove(m); 

                /// 通知所有觀察者 

                public string Notify() 

                        string s = ""; 

                        foreach (IMessage i in list) 

                        { 

                                s += i.Insert(_messageModel); 

                                s += "<br />"; 

                        } 

                        return s; 

                        get { return _messageModel.PublishTime; } 

                        set 

                                _messageModel.PublishTime = value; 

                                Notify(); 

MessageSubject

        /// Message主題（ConcreteSubject） 

        public class MessageSubject : AbstractMessageSubject 

                public MessageSubject(MessageModel mm) 

                        : base(mm) 

Test

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就會通知所有觀察者 

                // m.PublishTime = DateTime.Now; 

                Response.Write(m.Notify()); 

運作結果

sql方式：插入Message 2007-5-26 9:38:18

xml方式：插入Message 2007-5-26 9:38:18

參考

<a href="http://www.dofactory.com/Patterns/PatternObserver.aspx" target="_blank">http://www.dofactory.com/Patterns/PatternObserver.aspx</a>

OK

<a href="http://down.51cto.com/data/100859" target="_blank">[源碼下載下傳]</a>

     本文轉自webabcd 51CTO部落格，原文連結：http://blog.51cto.com/webabcd/344584，如需轉載請自行聯系原作者