In order to get the KeyStates we need to add handler to QueryContinueDrag. There the event arguments available are of type Telerik.Windows.DragDrop.QueryContinueDragEventArgs
which contain the DragDropKeyStates desired. More information about the drag source events and how to hook to them can be found here
You can try something like this in your code:
sender, Telerik.Windows.DragDrop.QueryContinueDragEventArgs e)
(e.KeyStates == DragDropKeyStates.ShiftKey)
//insert logic here.
Hopefully this helps.
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