ASP.NET自定义Web服务器控件-DropDownList/Select下拉列表控件

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
//自定义web服务器控件-下拉列表
namespace MyControls
{
    [DefaultProperty("Text")]
    [ToolboxData("<{0}:MySelect runat=server></{0}:MySelect>")]
    [ParseChildren(true,"Items")] //规定
    public class MySelect : WebControl
    {
        [Bindable(true)]
        [Category("Appearance")]
        [DefaultValue("")]
        [Localizable(true)]
        public string Text
        {
            get
            {
                String s = (String)ViewState["Text"];
                return ((s == null) ? String.Empty : s);
            }

            set
            {
                ViewState["Text"] = value;
            }
        }
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)] //以内容的形式打印标签
        public List<SelectItem> Items{
           get{
            if(ViewState["Items"]==null){
                ViewState["Items"] = new List<SelectItem>();
            }
               return (List<SelectItem>)ViewState["Items"];
           }
            set{
                ViewState["Items"] = value;
            }
        }

        [DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]//以内容的形式打印标签
        public Size Size
        {
            get
            {
                if (ViewState["Size"] == null)
                {
                    ViewState["Size"] = new Size();
                }
                return (Size)ViewState["Size"];
            }
            set
            {
                ViewState["Size"] = value;
            }
        }
        public override void RenderBeginTag(HtmlTextWriter writer)
        {
            this.Style.Add("Width", Size.Width + "px"); //增加样式，宽度
            this.Style.Add("Height", Size.Height + "px"); //增加样式，高度
            base.RenderBeginTag(writer);
        }
        protected override HtmlTextWriterTag TagKey
        {
            get
            {
                return HtmlTextWriterTag.Select;//下拉列表标签
            }
        }
        protected override void RenderContents(HtmlTextWriter output)
        {
            //打印下拉列表内容
            foreach(SelectItem item in Items){
                output.Write("<option value='"+item.Value+"'>"+item.Text+"</option>");
            }
        }
    }
}
using System;
using System.Collections.Gene