理解button的Click事件和TextBox的TextChanged\DropDownList.SelectedIndexChanged的实现原理的区别

using System;
using System.Web.UI;
using System.ComponentModel;
namespace control
{
 /// <summary>
 /// 理解button的Click事件和TextBox的TextChanged\DropDownList.SelectedIndexChanged的区别
 /// </summary>
 public class control1 : Control,IPostBackEventHandler,IPostBackDataHandler 
 {
  public control1()
  {
  }
  private string name;

  [BrowsableAttribute(true)]
  [DescriptionAttribute("姓名")]
  [DefaultValueAttribute("自定义名称")]
  [CategoryAttribute("aaa")]
  public virtual string PersonName
  {
   set
   {
    this.name=value;
   }
   get
   {
    return this.name;
   }
  }

  /// <summary>
  /// 老数据保存在ViewState中,如果禁用了ViewState则回传数据将失效
  /// </summary>
  public string Text
  {
   get
   {
    object text = ViewState["Text"];
    if (text == null)
     return string.Empty;
    else
     return (string)text;
   }
   set
   {
    ViewState["Text"] = value;
   }
  }

  

  protected override void Render(HtmlTextWriter writer)
  {
   writer.Write("<INPUT TYPE=submit name="+this.UniqueID+" Value='确定' /");   
   //writer.Write("<INPUT TYPE='text'   name="+this.UniqueID+" Value='"+this.Text+"' /");
   base.Render(writer);
  }

  #region 事件回传
//  public delegate void EventHandler(Object sender, EventArgs e);
//  public event EventHandler Click;
  public event EventHandler Click;//相当于上面两句
  protected virtual void OnMxhClick(System.EventArgs e)
  {
   if(Click!=null)
   {
    Click(this,e);
   }
  }
  public void RaisePostBackEvent(string eventArgument)
  {
   OnMxhClick(EventArgs.Empty);
  }
  #endregion

  #region 数据回传
  /// <summary>
  /// 判断是否调用RaisePostDataChangedEvent()
  /// </summary>
  /// <param name="postDataKey">传回来的新数据</param>
  /// <param name="postCollection"></param>
  /// <returns></returns>
  public bool LoadPostData(string postDataKey, System.Collections.Specialized.NameValueCollection postCollection)
  {
   string postData=postCollection[postDataKey];
   if(!Text.Equals(postData))
   {
    Text=postData;
    return true;//不同则自动调用RaisePostDataChangedEvent()函数
   }
   else
   {
    return false;
   }
  }

  public void RaisePostDataChangedEvent()
  {
   OnTextChanged(EventArgs.Empty);
  }

  public event EventHandler TextChanged;
  public void OnTextChanged(EventArgs e)
  {
   if(TextChanged!=null)
   {
    TextChanged(this,e);
   }
  }
  #endregion

 }
}