problem with treeview and iframe??

I have a master page which consists of a  tree view and an iframe,the links(which are links of other aspx pages) to the tree view were added dynamically(not through database but hard coded).
my question is when i click the tree view link i need to display the page in the iframe but i am getting it in a new window.there are about 20 links.I have written in the onselectednodechnage event some thing like this..but this event is not firing..
 protected void selectednode(object sender, eventargs e)
{
      ifrm.attributes.add("src", trview.selectednode.navigationurl.tostring());
}


 
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