创建非继承的自定义控件

    控件首先需要继承所有控件的基类：System.Web.UI.Control，并实现两个接口：Istate Manager（实现ViewState），IPostBackDataHandler（处理回发数据）。

TextBox
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.ComponentModel;

namespace Demo
{
    /**//// <summary>
    /// WebCustomControl1 的摘要说明。
    /// </summary>

    // 像前两个例子一样，先处理一下控件设计时属性。

    [DefaultProperty("Text"),
    Designer("Demo.DemoDesigner"),
    ToolboxData("<{0}:DemoTextBox runat=server></{0}:DemoTextBox>")]

    public class DemoTextBox : System.Web.UI.Control,IStateManager,IPostBackDataHandler
    {
        private StateBag _state;
        private bool _marked;

         //下面就是我们要实现的属性：Text

      [Bindable(true),
        Category("Appearance"),
        DefaultValue("")]

        public string Text
        {
            get
            {
                string _text = (string) ViewState["Text"];
                return _text==null?"":_text;
            }
            set
            {
                string text = "";
                text = value;
                text = text.Replace("'","’");
                ViewState["Text"] = text;
            }
        }

        //为了能实现视图状态就必须实现IStateManager接口

        object IStateManager.SaveViewState()
        {
                object _stateState = null;
                if( _state != null ) 
                    _stateState = ((IStateManager)_state).SaveViewState();
                if ( _stateState == null ) 
                    return null;
                return _stateState;
        }

         void IStateManager.TrackViewState()
        {
            _marked = true;
            if( _state != null )
                ((IStateManager)_state).TrackViewState();
        }

         void IStateManager.LoadViewState( object state )
        {
            if( state != null )
            {
                object _newState = (object)state;
                ((IStateManager)ViewState).LoadViewState( _newState );
            }
        }

        bool IStateManager.IsTrackingViewState 
        {
            get 
            {
                return _marked;
            }
        }

         internal new StateBag ViewState //注意，这里覆盖基类的ViewState属性
        {
            get 
            {
                if( _state == null ) 
                {
                    _state = new StateBag( true );
                    if( ((IStateManager)this).IsTrackingViewState )
                        ((IStateManager)_state).TrackViewState();
                }
                return _state;
            }
        }

        //下面把控件的表现输出到页面，其实System.Web.UI.WebControls.TextBox也是重新包装了Input而已。

        protected override void Render(HtmlTextWriter output)
        {
            string strOutput = "<Input name=\""+this.ClientID+"\" type=\"text\" value=\""+this.Text+"\">";
            output.Write(strOutput);
        }

        IPostBackDataHandler 成员#region IPostBackDataHandler 成员

        public void RaisePostDataChangedEvent()
        {
            // TODO:  添加 DemoTextBox.RaisePostDataChangedEvent 实现
        }

        //下面的方法很重要，把回发的数据保存。

        public bool LoadPostData(string postDataKey, System.Collections.Specialized.NameValueCollection postCollection)
        {
            // TODO:  添加 DemoTextBox.LoadPostData 实现
            string presentValue = this.Text;
            string postedValue = postCollection[postDataKey];

            if (!presentValue.Equals(postedValue))//如果回发数据不等于原有数据
            {
                this.Text = postedValue;
                return true;
            }
            return false;
        }
        #endregion
    }
}