ASP.NET常用控件之1：用于选择日期的TextBox控件

将日常使用的日期选择用户控件进行了封装，是我写的第一个服务器控件，希望大家给些意见。
using System;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Sdtcn.WebControls
{
    [
    Designer(typeof(Design.CompositeControlDesigner)) 
    ]
    public abstract class CompositeControl : 
        WebControl, INamingContainer 
    {
        public override ControlCollection Controls 
        {
            get 
            {
                EnsureChildControls();
                return base.Controls;
            }
        }
    }
}

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

namespace Sdtcn.WebControls
{
    /**//**//**//// <summary>
    /// CustomCalendar 的摘要说明。
    /// </summary>
    public class CustomCalendar : CompositeControl
    {
        private TextBox            _calendarTextBox;
        private HtmlInputButton _selectInputButton;
        private Calendar        _calendar;

        private static readonly object EventSelectChanged = new object();

        private string display
        {
            get
            {
                if(ViewState["Display"] == null)
                    return "none";
                else
                    return ViewState["Display"].ToString();
            }
            set
            {
                ViewState["Display"] = value;
            }
        }

        代理子控件的属性代理子控件的属性#region 代理子控件的属性
        [
        Bindable(true),
        Category("Appearance"),
        DefaultValue(""),
        Description("")
        ]
        public string CalendarText
        {
            get
            {
                EnsureChildControls();
                return _calendarTextBox.Text;
            }
        }

        [
        Bindable(true),
        Category("Appearance"),
        DefaultValue("Select"),
        Description("选择日期按钮的名称")
        ]
        public string SelectButtonText
        {
            get
            {
                EnsureChildControls();
                return _selectInputButton.Value;
            }
            set
            {
                EnsureChildControls();
                _selectInputButton.Value = value;
            }
        }


        #endregion

        事件事件#region 事件

        [
        Category("Action"),
        Description("选择日期后触发的事件")
        ]
        public event EventHandler SelectChanged
        {
            add
            {
                Events.AddHandler(EventSelectChanged,value);
            }
            remove
            {
                Events.RemoveHandler(EventSelectChanged,value);
            }
        }

        protected virtual void OnSelectChanged(object sender, EventArgs e) 
        {
            EventHandler selectChangedHandler = (EventHandler)Events[EventSelectChanged];
            if(selectChangedHandler != null)
            {
                selectChangedHandler(this,e);
            }
        }

        #endregion

        
        private void _calendar_SelectionChanged(object sender, EventArgs e) 
        {
            _calendarTextBox.Text = _calendar.SelectedDate.ToShortDateString();

            System.Web.UI.Control div = Page.FindControl("divCalendar");

            if(div is HtmlGenericControl)
            {
                ((HtmlGenericControl)div).Style.Add("display","none");
            }

            OnSelectChanged(sender,e);

            display = "none";
        }

        private void _calendar_VisibleMonthChanged(Object sender, MonthChangedEventArgs e)
        {
            display = "block";
        }

        public CustomCalendar()
        {}

        protected override void CreateChildControls()
        {
            Controls.Clear();

            _calendarTextBox = new TextBox();
            _calendarTextBox.ID = "calendarTextBox";
            _calendarTextBox.ReadOnly = true;

            _selectInputButton = new HtmlInputButton("button");
            _selectInputButton.Attributes.Add("Onclick","OnClick()");
            
            _calendar = new Calendar();
            _calendar.SelectionChanged += new EventHandler(_calendar_SelectionChanged);
            _calendar.VisibleMonthChanged += new MonthChangedEventHandler(_calendar_VisibleMonthChanged);

            this.Controls.Add(_calendarTextBox);
            this.Controls.Add(_selectInputButton);
            this.Controls.Add(_calendar);
        }

        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender (e);

            string script = "<script language=JavaScript> function OnClick(){  if( divCalendar.style.display == /"none/")    divCalendar.style.display = /"/";  else    divCalendar.style.display = /"none/";}</script>";
            Page.RegisterClientScriptBlock("script",script);
        }

        protected override void Render(System.Web.UI.HtmlTextWriter writer)
        {
            AddAttributesToRender(writer);

            _calendarTextBox.RenderControl(writer);
            _selectInputButton.RenderControl(writer);
            
            writer.Write("<br>");
            writer.RenderBeginTag(HtmlTextWriterTag.Div);
            writer.AddAttribute(HtmlTextWriterAttribute.Id,"divCalendar");
            writer.AddAttribute(HtmlTextWriterAttribute.Style,"DISPLAY:" + display + ";POSITION:absolute");
            _calendar.RenderControl(writer);
            writer.RenderEndTag();
        }

    }
}