Gets or sets the current edit value, which should be replaced by the new value.
The EditValueChanging event is raised when the editor's value is about to be changed (a user types or deletes a character, presses a spin button, etc.). The potential new value is returned by the event parameter's NewValue property. The current value is returned by the OldValue property. To cancel posting a NewValue to BaseEdit.EditValue, set the Handled and event parameter's IsCancel properties to true.