Specify Proxy Url as ASP.NET Binding Expression

[wexman]

Hi,

I would like to specify the URL of a HttpProxy of a store as ASP.NET binding expression (to a Settings value), for example:

<ext:Store ID="LookupStore" runat="server" AutoLoad="false">
   <Proxy>
      <ext:HttpProxy Method="GET" Url="<%# Properties.Settings.Default.ServiceRoot + "SomeService.svc/SomeMethod" %>" Json="true" />
   </Proxy>
   ...
</ext:Store>

This will result in the error (sorry, translated from German version, actual wording may be different): "Literal Content (...) is not allowed in Ext.Net.ProxyCollection".

The following, however, *will* work (bind to a simple property):

<ext:HttpProxy Method="GET" Url="<%# ServiceUrl %>" Json="true" />

What is the difference between the two (except the obvious, of course)? I mean, why does one work and the other don't?