如何给CheckBoxList和RadioButtonList添加滚动条？
继承基类CheckBoxList和RadioButtonList，添加滚动属性，重写Render方法即可。
属性列表：

#region 滚动控制
 private bool _ShowScrollBar = false;
 /// <summary>
 /// 显示滚动条
 /// </summary>
 [
 System.ComponentModel.Description("是否显示显示滚动条")
 , System.ComponentModel.DefaultValue(false)
 , System.ComponentModel.Category("滚动条设置")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public bool ShowScrollBar
 {
 get { return _ShowScrollBar; }
 set { _ShowScrollBar = value; }
 }
 private Overflow _OverflowY = Overflow.auto;
 /// <summary>
 /// 竖直滚动条
 /// </summary>
 [
 System.ComponentModel.Description("竖直滚动条")
 , System.ComponentModel.DefaultValue(Overflow.auto)
 , System.ComponentModel.Category("滚动条设置")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public Overflow OverflowY
 {
 get { return _OverflowY; }
 set { _OverflowY = value; }
 }
 private Overflow _OverflowX = Overflow.auto;
 /// <summary>
 /// 水平滚动条
 /// </summary>
 [
 System.ComponentModel.Description("水平滚动条")
 , System.ComponentModel.DefaultValue(Overflow.auto)
 , System.ComponentModel.Category("滚动条设置")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public Overflow OverflowX
 {
 get { return _OverflowX; }
 set { _OverflowX = value; }
 }
 private Unit _ScrollHeight = Unit.Parse("0px");
 /// <summary>
 /// 滚动高度
 /// </summary>
 [
 System.ComponentModel.Description("滚动高度")
 , System.ComponentModel.Category("滚动条设置")
 , DefaultValue("0px")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public Unit ScrollHeight
 {
 get { return _ScrollHeight; }
 set { _ScrollHeight = value; }
 }
 private Unit _ScrollWidth = Unit.Parse("0px");
 /// <summary>
 /// 滚动宽度
 /// </summary>
 [
 System.ComponentModel.Description("滚动宽度")
 , System.ComponentModel.Category("滚动条设置")
 , DefaultValue("0px")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public Unit ScrollWidth
 {
 get { return _ScrollWidth; }
 set { _ScrollWidth = value; }
 }
 private string _ScrollCssClass = "";
 /// <summary>
 /// 滚动样式设置
 /// </summary>
 [
 System.ComponentModel.Description("滚动样式设置")
 , System.ComponentModel.Category("滚动条设置")
 , System.ComponentModel.DefaultValue("")
 , System.ComponentModel.Bindable(System.ComponentModel.BindableSupport.Yes)
 ]
 public string ScrollCssClass
 {
 get { return _ScrollCssClass; }
 set { _ScrollCssClass = value; }
 }

 #region 书写标签
 void WriteBeginSpan(HtmlTextWriter writer)
 {
 if (this._ShowScrollBar)
 {
 StringBuilder strSpan = new StringBuilder();
 strSpan.Append("<span ");
 strSpan.Append(string.Format("style='overflow-y:{0};overflow-x:{1};",
 System.Enum.GetName(typeof(Overflow), this._OverflowY),
 System.Enum.GetName(typeof(Overflow), this._OverflowX)));
 if (this._ScrollHeight.ToString() != "0px")
 {
 strSpan.Append(string.Format("height:{0};", this._ScrollHeight));
 }
 if (this._ScrollWidth.ToString() != "0px")
 {
 strSpan.Append(string.Format("width:{0};", this._ScrollWidth));
 }
 strSpan.Append("';");
 if (!string.IsNullOrEmpty(_ScrollCssClass))
 {
 strSpan.Append(string.Format(" class='{0}'", _ScrollCssClass));
 }
 strSpan.Append(">");
 writer.Write(strSpan.ToString());
 }
 }
 void WriteEndSpan(HtmlTextWriter writer)
 {
 if (this._ShowScrollBar)
 {
 writer.Write("</span>");
 }
 }
 #endregion
 #endregion

重写Render方法： 

 protected override void Render(HtmlTextWriter writer)
 {
 this.WriteBeginSpan(writer);
 base.Render(writer);
 this.WriteEndSpan(writer);
 } 

就这样就可以了。
还要定义一个枚举：

public enum Overflow
 {
 auto = 0,
 hidden = 1,
 scroll = 2,
 visible = 3,
 inherit = 4
 }