《Asp.net服务器控件与组件开发》第9章的NavButton代码的个人研究

NavButton代码

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

namespace WebControlTestItem
{
 /// <summary>
 /// WebCustomControl 的摘要说明。
 /// </summary>
 [DefaultEvent("ClickNext"),
 DefaultProperty("NextText"),
 ToolboxData("<{0}:SimpleButton runat=server></{0}:SimpleButton>")
 ]
 public class SimpleButton:WebControl,IPostBackEventHandler
 {
  private string _nexttext;
  private string _previoustext;
  [Bindable(true),
  Category("外观"),
  DefaultValue("Next"),
  Description("显示在按钮上的文字")
  ]
  public virtual string NextText
  {
   get{ return((_nexttext==null)?String.Empty:_nexttext);}
   set{_nexttext=value;}
  }
  
  [Bindable(true),
  Category("外观"),
  DefaultValue("Previous"),
  Description("显示在按钮上的文字")
  ]
  public virtual string PreviousText
  {
   get{ return((_previoustext==null)?String.Empty:_previoustext);}
   set{_previoustext=value;}
  }

  /*protected override HtmlTextWriterTag TagKey
  {
    get { return HtmlTextWriterTag.Input;}
  }
  */
  //Click事件的键
  private static readonly object EventClickNext=new object();
  private static readonly object EventClickPreivous=new object();
  
  //事件属性
  [Category("操作"),Description("按下时触发按钮单击事件")]
  public event EventHandler ClickNext
  {
   add{
    Events.AddHandler(EventClickNext,value);
   }
   remove{Events.RemoveHandler(EventClickNext,value);}
  }

  [Category("操作"),Description("按下时触发按钮单击事件")]
  public event EventHandler ClickPreivous
  {
   add
   {
    Events.AddHandler(EventClickPreivous,value);
   }
   remove{Events.RemoveHandler(EventClickPreivous,value);}
  }

  protected virtual void OnClickNext(EventArgs e)
  {
   EventHandler clickHandler=(EventHandler)Events[EventClickNext];
   if(clickHandler!=null)
    clickHandler(this,e);
  }

  protected virtual void OnClickPreivous(EventArgs e)
  {
   EventHandler clickHandler=(EventHandler)Events[EventClickPreivous];
   if(clickHandler!=null)
    clickHandler(this,e);
  }
  
  /*protected override void AddAttributesToRender(HtmlTextWriter writer)
  {
   base.AddAttributesToRender(writer);
   writer.AddAttribute(HtmlTextWriterAttribute.Name,this.UniqueID);
   writer.AddAttribute(HtmlTextWriterAttribute.Type,"submit");
   writer.AddAttribute(HtmlTextWriterAttribute.Value,this.Text);
  }*/
  

  #region IPostBackEventHandler 成员

  public void RaisePostBackEvent(string eventArgument)
  {
   // TODO:  添加 SimpleButton.RaisePostBackEvent 实现
   if(eventArgument=="下一步")
    OnClickNext(EventArgs.Empty);
   if(eventArgument=="上一步")
    OnClickPreivous(EventArgs.Empty);
  }

  #endregion
  protected override void Render(HtmlTextWriter writer)
  {
   if(Page!=null)
    Page.VerifyRenderingInServerForm(this);
   base.Render (writer);

  }
  protected override void RenderContents(HtmlTextWriter writer)
  {
   base.RenderContents (writer);
   writer.AddAttribute(HtmlTextWriterAttribute.Onclick,Page.GetPostBackEventReference(this,"上一步"));
   writer.AddAttribute("language","javascript"); //此句非必须
   writer.RenderBeginTag(HtmlTextWriterTag.Button);
   writer.Write(this.PreviousText);
   writer.RenderEndTag();
   
   writer.Write("&nbsp;&nbsp;");

   writer.AddAttribute(HtmlTextWriterAttribute.Onclick,Page.GetPostBackEventReference(this,"下一步"));
   writer.AddAttribute("language","javascript");//此句非必须
   writer.RenderBeginTag(HtmlTextWriterTag.Button);
   writer.Write(this.NextText);
   writer.RenderEndTag();

  }

 }
}

以上代码是按照书第9章的NavButton代码修改的代码，原书中属性是用ViewState字典做的，但运行时按钮上没有任何字符，我把它改成普通属性，就好了。
另外，PreviousText和NextText不能设置为Previous和Next，否则运行时按钮上也没有任何字符。这一点很让人困惑。注释部分是书上前一个例子的代码。