自定义复合控件[2]-引发缓存事件

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;

namespace csMathControl
{
    /// <summary>
    /// 引发缓存事件
    /// </summary>
    [DefaultProperty("Text"), 
        ToolboxData("<{0}:RenderText runat=server></{0}:RenderText>")]
    public class RenderText : System.Web.UI.WebControls.WebControl
    {
        
        [Bindable(true), 
            Category("Appearance"), 
            DefaultValue("")] 
        public string Text 
        {
            get
            {
                if(ViewState["text"]!=null)
                return ViewState["text"].ToString();
                else
                    return null;
            }
            set
            {
                ViewState["text"] = value;
                OnChange(EventArgs.Empty);
            }
        }
        /// <summary> 
        /// 将此控件呈现给指定的输出参数。
        /// </summary>
        /// <param name="output"> 要写出到的 HTML 编写器 </param>
        protected override void Render(HtmlTextWriter output)
        {
            //output.Write(Text);
            output.AddAttribute("value",this.Text );
            output.RenderBeginTag("INPUT");
            output.RenderEndTag();
        }
        //---------------事件--------------------
        ///
        public event EventHandler Change;
        protected virtual void OnChange(EventArgs e)
        {
            if(Change!=null)
                Change(this,e);
        }
        //----------------------------------
    }
}