If I understand you correctly, you need to set the size of RadWindow in the
code behind of the content page. Since the resizing of the window can be done on the client only, you could do this by calling a JavaScript function from server code
by registering it with the RegisterStartupScript() function.
You can find a simple demonstration of this approach in the attached archive file.
I hope this helps.
Sincerely yours,
Fiko
the Telerik team
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