extension slight cost container.dataitem?

so i have an ilist business entities i loop by listview an unordered list. i combined an progression slight entity display layer. formula behind, i response.write outcome progression method, nonetheless i try opening by listview i an error. slight called iscurrent advantage bool... here code:

<li><%#((cb.cmsframework.webpage)container.dataitem).iscurrent(guid.empty) %></li>

the blunder i is: 'cb.cmsframework.webpage' does enclose construction 'iscurrent' progression slight 'iscurrent' usurpation initial justification form 'cb.cmsframework.webpage' found (are blank controlling gauge an public reference?)

however... i blunder i form formula code behind:

webpage w = new webpage();
response.write(w.iscurrent(guid.empty));