HTML asp PostBackUrl ?

Is there a way to add the HiddenField value to the PostBackUrl as a variable?

Consider this code -


<asp:Button PostBackUrl="~/Default.aspx" ID="Button1" runat="server"  Text="ASP BUTTON" /></div>
   
<asp:HiddenField ID="SaveXML" runat=server Value="False" />

Something like this -


<asp:Button **PostBackUrl="~/Default.aspx?Cmd=&"+SaveXML.value** ID="Button1" runat="server"  Text="ASP BUTTON" /></div>

I’m really running into a brick wall here. Iv’e tried an on click event to call a sub routine, but the first think that happens when you click the button is the page_load event fires and clears out all the hidden variables. Very strange. Maybe the PostBackUrl can save me.