NullReferenceException on ASP.NET PreviousPage Property

I followed the directions from MSDN on transferring data between asp.net pages.

But when using the 'PreviousPage' property to access the previous pages controls, I get a null ref exception that PreviousPage is not set to an instance of an object.

Here is my code:

public partial class Portal : System.Web.UI.Page
{
    public string Username
    {
        get
        {
            return txt_User.Text;
        }
    }

And this is the submit button on initial page:

<asp:Button ID="btn_Submit" runat="server" onclick="btn_Submit_Click" 
    PostBackUrl="~/Query.aspx"

Previous page property on second page:

    protected void Page_Load(object sender, EventArgs e)
    {
        Username = PreviousPage.Username; 
    }

As per MSDN instructions I also added this at the top of the second pages markup file:

<%@ PreviousPageType VirtualPath="~/Portal.aspx" %> 

Also note I have tried Server.Transfer to switch pages instead and that produces the same error.

EDIT, h开发者_StackOverflow社区ere is using Server.Transfer on the initial page click event:

 protected void btn_Submit_Click(object sender, EventArgs e)
    {
        Server.Transfer("Query.aspx"); 
    }

EDIT, button code without event handler:

<asp:Button ID="btn_Submit" runat="server"
    PostBackUrl="~/Query.aspx"
    style="height: 26px" Text="Submit" />

---

This works fine for me. If PreviousPage is null, that generally indicates the current page was not displayed as a result of a cross-page postback.

Can you confirm the error is being raised on the second page?

Also, what the onclick="btn_Submit_Click" in your button definition? There should be no code responding to the click event on the original page. Remember, it will be handled by the target page.

EDIT: Now that you've updated your question, my last point seems to be the issue. You are doing a server transfer from the original page. This is NOT a cross-page postback and that's why PreviousPage is null.

Remove the onclick attribute from your button and delete btn_Submit_Click.