如何在两个页面传递数据?

我去找了个例程
<%@ Page language="c#" Codebehind="firstpage.aspx.cs" AutoEventWireup="false" ClassName="FirstPageClass" Inherits="test.WebForm1" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<script runat="server">
public string FirstName
{
get
{
return first.Text;
}
}
public string LastName
{
get
{
return last.Text;
}
}
void ButtonClicked(object sender, EventArgs e)
{
Server.Transfer("secondpage.aspx");
}
</script>
</HEAD>
<body>
<form id="Form1" runat="server">
First Name:
<asp:textbox id="first" runat="server"></asp:textbox><br>
Last Name:
<asp:textbox id="last" runat="server"></asp:textbox><br>
<asp:button id="Button1" onclick="ButtonClicked" runat="server" Text="Go to second page"></asp:button></form>
</body>
</HTML>
×××××××××××××××××××××××××××××××××××××
<%@ Page language="c#" Codebehind="secondpage.aspx.cs" Debug="True" AutoEventWireup="false" Inherits="test.secondpage" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<%@ Reference Page="firstpage.aspx" %>
<html>
<head>
<script runat="server">
FirstPageClass fp;
void Page_Load()
{
if (!IsPostBack)
{
fp = (FirstPageClass)Context.Handler;
}
}
</script>
</head>
<body>
<form runat="server" ID="Form1">
Hello <%=fp.FirstName%> <%=fp.LastName%>
</form>
</body>
</html>
firstpage里的Textbox的值应该传给secondpage,但是我运行的时候总提示
Object reference not set to an instance of an object.
为什么？我该怎么改呀？