Cori, you are right (assuming that the window
object in your code refers to the RadWindow object and not the browser's one).
Alan, I have already answered your support ticket on the same subject - for convenience I will paste part of my reply below, as it answers Jared's question too.
Basically, RadWindow's AutoSize feature works automatically on page load. When you initially load the page in the control, RadWindow will check the size of the content and will resize itself accordingly. It however, does not monitor the content constantly as that would severely degrade the performance. That is why if you dynamically change the size of the content (by expanding the treeview), you need to manually call autoSize() again, so the changes affect the size of the window.
RadTreeview has an OnClientNodeExpanded property that allows you to hook to the nodeExpanded event. You can call autoSize() there (a small timeout may be needed so the RadWindow would take the correct page's size). This approach was used in our Returning Values from a Dialog demo where RadWindow is auto-sized on datepicker's OnPopupOpening / OnPopupClosing events.
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