因为内容页比母版页先加载，所以母版页里的实体不能在Page_Load中赋值。应该重写OnInit，所以在母版页中的cs重写：

 protected override void OnInit(EventArgs e)
    {
        sqlstr = "select top 1  * from shouYe order by ID desc";
        dt = dbHepler.CreateDataTable(sqlstr);
        IList<WebInfo> webinfos = new List<WebInfo>();
        webinfos = ConvertHelper.convertToList<WebInfo>(dt);
        singlewebinfo = webinfos[0];
    }

然后再内容页中：

 public WebInfo webinfo = new WebInfo();//实例一个实体

 protected void Page_Load(object sender, EventArgs e)
    {
        webinfo = (WebInfo)((Mp1)this.Master).singlewebinfo;
}