ajax 问题

[shulei521]

没放ajax 更新面版 没有错误
放了以后
下面代码就提示不能实例化
protected void Page_PreInit(object sender, EventArgs e)
{
if (Request["DropDownList1"] != null)
{
Theme = Request["DropDownList1"].ToString();
}
if (Theme == "None")
{
Theme = "";
GridView1.SkinID = "";

}
if (Theme != String.Empty)
{
GridView1.SkinID = Theme.Substring(2);
}


}