How to add a scroll bar for CheckBoxList and RadioButtonList-practical tips

How do I add scroll bars to CheckBoxList and RadioButtonList?
inherits the base class CheckBoxList and RadioButtonList , Add scrolling properties and rewrite the Render method.
Properties list:

#region scroll control
    private bool _ShowScrollBar = false;
    /// <summary>
    /// show scroll bar
    /// </ summary>
    [
    System.ComponentModel.Description ("Whether to show the scroll bar")
    , System.ComponentModel.DefaultValue (false)
    , System.ComponentModel.Category ("Scroll bar settings")
    , System.ComponentModel.Bindable (System.ComponentModel.BindableSupport.Yes)
    ]
    public bool ShowScrollBar
    {
      get {return _ShowScrollBar;}
      set {_ShowScrollBar = value;}
    }
    private Overflow _OverflowY = Overflow.auto;
    /// <summary>
    /// vertical scroll bar
    /// </ summary>
    [
    System.ComponentModel.Description ("Vertical scroll bar")
    , System.ComponentModel.DefaultValue (Overflow.auto)
    , System.ComponentModel.Category ("Scroll bar settings")
    , System.ComponentModel.Bindable (System.ComponentModel.BindableSupport.Yes)
    ]
    public Overflow OverflowY
    {
      get {return _OverflowY;}
      set {_OverflowY = value;}
    }
    private Overflow _OverflowX = Overflow.auto;
    /// <summary>
    /// horizontal scroll bar
    /// </ summary>
    [
    System.ComponentModel.Description ("Horizontal scroll bar")
    , System.ComponentModel.DefaultValue (Overflow.auto)
    , System.ComponentModel.Category ("Scroll bar settings")
    , System.ComponentModel.Bindable (System.ComponentModel.BindableSupport.Yes)
    ]
    public Overflow OverflowX
    {
      get {return _OverflowX;}
      set {_OverflowX = value;}
    }
    private Unit _ScrollHeight = Unit.Parse ("0px");
    /// <summary>
    /// scroll height
    /// </ summary>
    [
    System.ComponentModel.Description ("Scroll height")
    , System.ComponentModel.Category ("Scroll bar settings")
     , 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>
    /// scroll width
    /// </ summary>
    [
    System.ComponentModel.Description ("Scroll width")
    , System.ComponentModel.Category ("Scroll bar settings")
    , DefaultValue ("0px")
    , System.ComponentModel.Bindable (System.ComponentModel.BindableSupport.Yes)
    ]
    public Unit ScrollWidth
    {
      get {return _ScrollWidth;}
      set {_ScrollWidth = value;}
    }
    private string _ScrollCssClass = "";
    /// <summary>
    /// scroll style settings
    /// </ summary>
    [
    System.ComponentModel.Description ("Scroll style settings")
    , System.ComponentModel.Category ("Scroll bar settings")
    , System.ComponentModel.DefaultValue ("")
    , System.ComponentModel.Bindable (System.ComponentModel.BindableSupport.Yes)
    ]
    public string ScrollCssClass
    {
      get {return _ScrollCssClass;}
      set {_ScrollCssClass = value;}
    }

    #region Writing tags
    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

To override the Render method:

 protected override void Render (HtmlTextWriter writer)
    {this
      . Writebeginspan (writer);
      Base. Render (writer);
      This. Writeendspan (writer);
    } 

That's it for you.
You also define an enumeration:

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

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