Generally, events are intended to be used as an indication that the user has performed a certain action. So, calling them inside your code is not a recommended way to go. Why not performing the logic inside the code that updates the value?
Nevertheless, BeginningEdit event can be called as any other:
var editArgs = new PropertyGridBeginningEditEventArgs()
RoutedEvent = RadPropertyGrid.BeginningEditEvent
But still, please keep in mind that events are supposed to be raised by the UI, not by some logic inside the end user code.
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and share your thoughts.