Unfortunately, RadDataFilter does not have such events.
You could attach to RadDataFilter.FilterDescriptors.CollectionChanged and RadDataFilter.FilterDescriptors.ItemChanged and listen for various changes there. Use the debugger to see what is thrown when.
Basically, ItemChanged will be fired each time when something (Member-Operator-Value) of a filter changes somewhere in the filter tree. But I am not sure whether this will suit your needs.
I hope this helps.
the Telerik team
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