重载此警告窗口,使某控件获得焦点

 /// <summary>
  /// 服务器端弹出alert对话框，并使控件获得焦点
  /// </summary>
  /// <param name="str_Ctl_Name">获得焦点控件Id值,比如：txt_Name</param>
  /// <param name="str_Message">提示信息,例子："请输入您姓名!"</param>
  /// <param name="page">Page类</param>
  public void Alert(string str_Ctl_Name,string str_Message,Page page)
  {
   page.RegisterStartupScript("","<script>alert('"+str_Message+"');document.forms(0)."+str_Ctl_Name+".focus(); document.forms(0)."+str_Ctl_Name+".select();</script>");
  }