可编辑下拉列表框

在有些项目中经常会遇到下拉列表框里内容不够的情况下，允许输入，．ＮＥＴ里没有现成的组件，现在我以Ｃ＃写了一个，希望高手指教

using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;
using System.Collections ;
using System.Collections.Specialized ;
using System.Drawing;

namespace DongLan.ControlLibrary
{
    /**//// <summary>
    /// Dropdown 可编辑的下拉列表框。
    /// 2006-1-4
    /// </summary>
    /// 

    [DefaultProperty("Items"),
    ToolboxData("<{0}:Dropdown runat=server></{0}:Dropdown>")] 
    public class DropDown : System.Web.UI.WebControls.WebControl
    {
        内部成员#region 内部成员
        private System.Web.UI.WebControls.DropDownList m_oDDList;
        private System.Web.UI.WebControls.TextBox      m_oTxtList;
        #endregion

        公开的属性#region 公开的属性

        [Bindable(true), Category("Appearance"), DefaultValue("")]
        public string Text
        {
            get
            {
                EnsureChildControls();
                if (m_oTxtList != null)
                {
                    return m_oTxtList.Text;
                }
                else
                {
                    return null;
                }
                
            }
            set
            {
                EnsureChildControls();
                m_oTxtList.Text = value;
                
            }
        }
        [Category("Behavior")]
        public bool AutoPostBack 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.AutoPostBack;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.AutoPostBack = value;
            }
        }

        [Category("Data")]
        public string DataMember 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.DataMember;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.DataMember = value;
            }
        }

        [Category("Data"),
        DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden),
        BindableAttribute(true)]
        public object DataSource 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.DataSource;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.DataSource = value;
            }
        }


        [Category("Data")]
        public string DataTextField 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.DataTextField;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.DataTextField = value;
            }
        }

        [Category("Data")]
        public string DataTextFormatString 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.DataTextFormatString;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.DataTextFormatString = value;
            }
        }

        [Category("Data")]
        public string DataValueField 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.DataValueField;
            }
            set
            {
                EnsureChildControls();
                m_oDDList.DataValueField = value;
            }
        }

        [Browsable(false)]
        public ListItemCollection Items 
        {
            get
            {
                EnsureChildControls();
                return m_oDDList.Items;
            }
        }

        
        [Browsable(false), Bindable(true)]
        public string Value
        {
            get
            {
                EnsureChildControls();
                return m_oTxtList.Text;
            }
            set
            {
                EnsureChildControls();
                m_oTxtList.Text = value;
            }
        }
        #endregion

        重载#region 重载
        public override ControlCollection Controls
　　    {
　　　        get
　　　        {
　　　　        EnsureChildControls(); //确认子控件集都已被创建
　　　　        return base.Controls;
　　　        }
　　    }

        protected override void CreateChildControls()
　　    {
            Controls.Clear();
            
            m_oDDList                    = new DropDownList();
        
            m_oDDList.EnableViewState   = true;
            m_oDDList.Style.Add("width","127");
            m_oDDList.Style.Add("CLIP","rect(3px 130px 20px 110px)");
            m_oDDList.Style.Add("POSITION","absolute");
            m_oDDList.SelectedIndexChanged += new EventHandler(m_oDDList_SelectedIndexChanged);
            this.Controls.Add(m_oDDList);


            m_oTxtList = new System.Web.UI.WebControls.TextBox();
            m_oTxtList.AutoPostBack = false;
            m_oTxtList.EnableViewState = true;
            m_oTxtList.Wrap = true;
            m_oTxtList.Style.Add("width","127");
            Controls.Add(m_oTxtList);

            
            
            
        }

        protected override void OnDataBinding(EventArgs e)
        {
            EnsureChildControls();
            m_oDDList.DataBind();
            m_oTxtList.DataBind();
            base.OnDataBinding (e);
        }
        #endregion

        事件#region 事件
        private static readonly object EventSelectedIndexChanged = new object();
        public event EventHandler SelectedIndexChanged
        {
            add
            {
                Events.AddHandler(EventSelectedIndexChanged, value);
            }
            remove
            {
                Events.RemoveHandler(EventSelectedIndexChanged, value);
            }
        }

        #endregion

        private void m_oDDList_SelectedIndexChanged(object sender, EventArgs e)
　　    {
　　　        this.Text   = m_oDDList.SelectedValue.ToString();
            this.OnSelectedIndexChanged(e);
　　
　　    }
        protected virtual void OnSelectedIndexChanged(EventArgs args)
        {
            EventHandler onSelectedIndexChanged = (EventHandler)Events[EventSelectedIndexChanged];
            if(onSelectedIndexChanged != null)
                onSelectedIndexChanged(m_oDDList, args);
        }

//        protected override void OnPreRender(EventArgs e)
//        {
//            base.OnPreRender(e);
//        }
        protected override void Render(HtmlTextWriter output)
        {

            output.WriteLine("<script language=\"JavaScript\">");
            output.WriteLine("function SelectDroup(txtName,DropuName){");
            output.WriteLine("txtName.value=DropuName.options(DropuName.selectedIndex).text");
            output.WriteLine("}");
            output.WriteLine("</script>");
            m_oDDList.Attributes.Add("onchange","javascript:SelectDroup("+m_oTxtList.ClientID+",this);");
            m_oDDList.RenderControl(output);
            m_oTxtList.RenderControl(output);
        }

    }
}