自定义控件实现WebControl和Compositecontrol得区别

1. 当你的自定义控件实现WebControl或者Control类时候，如果你在重写 CreateChildControls方法来创建控件，那么你在重写Render方法来实现拖拽到页面控件自动生成，那么你必须在Render方法中在调用每个控件的RenderControl()方法之前调用 EnsureChildControls() 方法来确保控件不为NULL而导致的异常.

     public   class  MyControls : WebControl
    {
         private  Button bt;
         protected   override   void  CreateChildControls()
        {
             base .CreateChildControls();
            Controls.Clear();
            bt  =   new  Button();
            bt.ID  =   this .ClientID;
            bt.Text  =   " Submit " ;
            Controls.Add(bt);
        }
         protected   override   void  Render(HtmlTextWriter writer)
        {
             base .Render(writer);
            EnsureChildControls();
            bt.RenderControl(writer);
        }
    }

如果你的自定义控件实现CompositeControl,因为在Render方法中如果判断在设计界面，那么编译器会强迫调用EnsureChildControls()
方法调用CreateChildControls()方法创建控件。所以你无需在Render方法中再次调用。

protected   internal   override   void  Render(HtmlTextWriter writer)
{
     if  ( base .DesignMode)
    {
         this .EnsureChildControls();
    }
     base .Render(writer);
}

//完整实例

using  System;
using  System.Collections.Generic;
using  System.Linq;
using  System.Text;
using  System.Web.UI;
using  System.Web.UI.WebControls;
using  System.ComponentModel;
using  System.Collections.Specialized;
namespace  MyCustomizeControl
{

     public   class  MyControl : CompositeControl,IPostBackDataHandler
    {
         private   static   readonly   object  objLock  =   new   object ();
         private   static   readonly   object  objLock2  =   new   object ();

         private  TextBox txb;
         private  Button bt;
         private  LinkButton lnk_Submit;

         private   string  _strText  =   string .Empty;
         public   string  strUser
        {
             get
            {
                EnsureChildControls();
                 return  (ViewState[ " strUser " ]  ==   null )  ?   string .Empty : ViewState[ " strUser " ].ToString();
            }
             set
            {
                EnsureChildControls();
                ViewState[ " strUser " ]  =  value;
            }
        }

         public   event  EventHandler MyClick
        {
            add {
                Events.AddHandler(objLock, value);
            }
            remove
            {
                Events.RemoveHandler(objLock, value);
            }
        }
         public   event  EventHandler MyLinkClick
        {
            add
            {
                Events.AddHandler(objLock2, value);
            }
            remove
            {
                Events.RemoveHandler(objLock2, value);
            }
        }

         protected   void  OnHandler(EventArgs e)
        {
            EventHandler eventDelegate  =  Events[objLock]  as  EventHandler;
             if  (eventDelegate  !=   null )
            {
                eventDelegate( this , e);
            }
        }
         protected   void  OnLinkHandler(EventArgs e)
        {
            EventHandler eventDelegate  =  Events[objLock2]  as  EventHandler;
             if  (eventDelegate  !=   null )
            {
                eventDelegate( this , e);
            }
        }

         public   string  SubmitName
        {
             get  {
                 return   this .ClientID  +   " _Submit " ;
            }
        }
         public   string  LinkButtonName
        {
             get
            {
                 return   this .ClientID  +   " _LinkButton " ;
            }
        }
         public   string  TextBoxName
        {
             get
            {
                 return   this .ClientID  +   " _TxtName " ;
            }
        }

         protected   override   void  CreateChildControls()
        {
            // base.CreateChildControls();
            txb  =   new  TextBox();
            txb.ID  =  TextBoxName;

            bt  =   new  Button();
            bt.ID  =  SubmitName;
            bt.Text  =   " Submit " ;

            lnk_Submit  =   new  LinkButton();
            lnk_Submit.Text  =   " MyLink " ;
            lnk_Submit.ID  =  LinkButtonName;

            Controls.Add(lnk_Submit);
            Controls.Add(txb);
            Controls.Add(bt);                  
        }

         private   string  _stringUserName  =   string .Empty;
         public   string  UserName
        {
             get  {
                EnsureChildControls();
                 return  (ViewState[ " UserName " ]  ==   null )  ?   string .Empty : ViewState[ " UserName " ].ToString();
            }
             set  {
                EnsureChildControls();
                ViewState[ " UserName " ]  =  value;
            }
        }
         protected   override   void  OnPreRender(EventArgs e)
        {
             base .OnPreRender(e);
             if  ( this .Page  !=   null   &&   this .Enabled)
            {
                 this .Page.RegisterRequiresPostBack( this );
            }
        }
         protected   override   bool  OnBubbleEvent( object  source, EventArgs args)
        {
             if  (source.GetType()  ==   typeof (System.Web.UI.WebControls.LinkButton))
            {
                OnLinkHandler(EventArgs.Empty);
            }
             // if (source.GetType() == typeof(System.Web.UI.WebControls.Button))
            //  {
                OnHandler(EventArgs.Empty);
            //  }
             return   true ; // base.OnBubbleEvent(source, args);
        }


         #region  IPostBackDataHandler Members

         public   bool  LoadPostData( string  postDataKey, NameValueCollection postCollection)
        {
            NameValueCollection nvc  =  postCollection;
             string  str  =  nvc[postDataKey  +   " $ "   +  TextBoxName];
             if  (UserName  !=  str)
            {
                UserName  =  str;
                 return   true ;
            }
             else   return   true  ;
           //   throw new NotImplementedException();
        }

         public   void  RaisePostDataChangedEvent()
        {
            Context.Response.Write( " hello " );
            //  throw new NotImplementedException();
        }

         #endregion
    }

}