Attached is a sample page, which shows how the advanced form of the RadScheduler (when not bound to a web service) could be hidden without making a post-back to the server. The sample uses a simple user control as an advanced edit form.
You should keep in mind that the modal property of the advanced form should be set to true, in order to see the RadScheduler when the button to hide the advanced from is clicked.
Also, have you considered using a web service binding as a data source for the RadScheduler. The closing of the advanced form when bound to a web service does not make a post-back to the server.
More information about the web service binding could be found at the following help article: RadScheduler: Web Service Binding
and/or the online web service binding demo at our web site: RadScheduler: Web Service Binding / Demo
Hope this helps.
the Telerik team
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