Since you can't directly view a master page I'm assuming you have two pages which use a common master page. I am also assuming that this master page displays a drop down list and a treeview sitemap.
Based on this I would think that what is mostly happening is that your treeview is rendering plain old html links (i.e. <a href='http://stackoverflow.com'>...
). When these are clicked your browser executes a get request for the second child page. By default no data from the first child page is passed to the second.
There are various ways to change this behavior. First you should set the AutoPostBack
property to true and the handle SelectedIndexChanged
event on your dropdownlist. In that event you can save the value of the dropdown so that it can be restored later.
The easiest way to save this value is probably to put it in the session.
Session["myvar"] = dropdown.SelectedIndex;
Your master page can restore this value when the child page loads by doing something like:
if (!IsPostBack && Session["myvar"] != null)
dropdown.SelectedIndex = (int)Session["myvar"];
Another option would be to add the value to the querystring of each url in the treeview.