RangeSelectionChanged
RadDatePicker provides the RangeSelectionChanged server event, which is triggered when the user changes the value of the control and a Postback is done so the change gets submitted to the server.
The event handler is not called unless the date and/or time actually changes. If the user makes a change that results in the same value (for example, typing a different string that parses to the same value), a postback occurs but the RangeSelectionChanged event handler is not triggered.
The RangeSelectionChanged event handler receives two arguments:
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The control whose value has just changed. This argument is of type object, but can be cast to the appropriate type. 
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A RangeSelectionChangedEventArgs object. This object has the following two properties: - 
StartDate is the Start Date value after the change. 
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EndDate is the End Date value after the change. 
 
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You can use this event to respond in server-side code when the user changes the value.