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
    }

}