Hyperlink won't work when creating a unique url? C# asp.net

Question

<asp:SqlDataSource ID="itemsforsale" runat="server"
     ConnectionString="<%$ ConnectionStrings:ElmtreeConnection  %>"
     SelectCommand="SELECT * FROM Products WHERE Products.CategoryId = @CategoryId">

     <SelectParameters>
         <asp:QueryStringParameter Name="CategoryId" 
              QueryStringField="CategoryId" Type="Int32" />
     </SelectParameters>
</asp:SqlDataSource>

<asp:HyperLink ID="hyperlink" runat="server" 
     NavigateUrl='<%# "ItemsForSale.aspx?CategoryId"+Eval("CategoryId") %>' 
     Text="Beauty"></asp:HyperLink>

This is my markup. I'm not getting any errors when loading the page, however the link is not working. Can anyone give me any insight as to why?

Answer 1

An equal sign is missing in the URL:

NavigateUrl='<%# "ItemsForSale.aspx?CategoryId=" + Eval("CategoryId") %>'

If the HyperLink is not in a databound control, you must call its DataBind method (or the DataBind method of the Page itself) in Page_Load to make sure that its databinding expression is evaluated:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        hyperlink.DataBind();
        ...
    }
}

Answer 2

You're essentially creating a Url to the address ItemsForSale.aspx. Prefix your URL with ~/ to have it recognized as a route relative to your base url.