I am not sure I understand you completely, yet I can suggest you try a combination of the following
- a check if you are inside a RadWindow (which is explained here
- in case you are in a RadWindow you can avoid using a OnCilentClose handler, but instead simply call a function from the parent page
in the same place where you close the second level RadWIndow (i.e. the button OnClientClick handler)
This may require that you add a function to handle this logic in all parents that may host your user control, however, yet there isn't a better approach to handle a user control that depends on its context, as generally user controls should not depend on the context/parent. You could further extend this if you like to use the same approach for all cases - i.e. calling a function from the parent page instead of an onclientclose handler.
the Telerik team
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