深入剖析Asp.net组件设计(1)：WebTimer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Web.UI;
using System.ComponentModel;

namespace WebTimer
{
    public class WebTimer:Control,IPostBackEventHandler
    {
        #region 成员        
        private Int32 _interval = 5000;

        private Boolean _enabled = false;
        private static readonly object EventTimer = new object();
        #endregion
        #region属性        
        [DefaultValue(5000),Bindable(false),Description("延迟毫秒数")]
        public Int32 Interval
        {
            get { return _interval; }
            set { _interval = value; }
        }

        public Boolean Enable
        {
            get { return _enabled; }
            set { _enabled = value; }
        }

        #endregion
        /// <summary>
        /// 定义事件
        /// </summary>
        #region 事件
        public event EventHandler Timer
        {
            add {
                //将委托添加到控件的委托列表中，value是一个委托，此方法包含
                //this.Timer+=EventHandler(Id_Timer);
                Events.AddHandler(EventTimer, value);
            }
            remove {
                Events.RemoveHandler(EventTimer, value);
            }
        }
        /// <summary>
        /// 在执行时postback时调用
        /// </summary>
        /// <param name="e"></param>
        protected virtual void OnTimer(EventArgs e)
        {

            EventHandler timerHandler = (EventHandler)Events[EventTimer];
            if (timerHandler != null)
            {   //执行所有向Timer事件注册的方法：ID_Timer(sender,e)
                timerHandler(this, e);
            }
          
        }
        #endregion

        /// <summary>
        /// 实现接口：在PostBack事件中调用OnTimer函数
        /// </summary>
        /// <param name="eventArgument"></param>
        #region 接口        
        public void RaisePostBackEvent(string eventArgument)
        {
            //事件发生调用OnTimer函数
            OnTimer(EventArgs.Empty);
        }
        #endregion

        #region 核心Js：setTimeOut函数
        private string buildJs()
        {
            StringBuilder str = new StringBuilder();
            str.Append("<script language='JavaScript'>\n<!-- ");
            str.AppendFormat("\n setTimeout(\"{0}\",{1});",
                new object[] { this.Page.GetPostBackEventReference(this), _interval.ToString() });
            str.Append("\n//-->\n</script>");
            return str.ToString();

        }
        #endregion
        
        #region 重载OnPreRender、Render
        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);
            Page.GetPostBackEventReference(this, "");
        }
        protected override void Render(HtmlTextWriter writer)
        {
             base.Render(writer);
             if (Page!=null)
             {
                 Page.VerifyRenderingInServerForm(this);
             }
             if (_enabled)
             {
                 writer.Write(buildJs());
             }
        }
        #endregion
        
    }
}