在这里我只做两种皮肤的切换，
1.首先要做两个框架结构相同的母板页；
2.新建内容页，引用默认母板页；
3.在新建页面的.cs文件里写上：
Codeprotected void Page_PreInit(object sender, EventArgs e)
{
if (Request.Cookies["Theme"] != null)
{
this.Theme = Request.Cookies["Theme"].Value;
this.MasterPageFile = "~/" + Request.Cookies["Theme"].Value + ".master";
}
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack && Request.Cookies["Theme"] != null)
this.DropDownList1.SelectedValue = Request.Cookies["Theme"].Value;
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
Response.Cookies["Theme"].Value = DropDownList1.SelectedValue;
Response.Redirect(Request.Url.AbsoluteUri);
}