AutoCompletion API

I am implementing my own auto completion stuff using CompletionContributor and CompletionProvider. Is there any way to know which item the user chooses from the list of suggestions? For example, the auto-completion engine shows two suggestions: 'A', 'B'. And the user chooses B. Of course we can compare the texts after 'B' is inserted in order to know which item is selected. But is there an API to automatically capture this user action?