Subcribe to active document changes?

[lsoft]

Hi!

I need to subscribe to change events in (any) active document. I found the following

            var adv = await VS.Documents.GetActiveDocumentViewAsync();
            if (adv != null)
            {
                adv.TextBuffer.ChangedLowPriority += TextBufferChanged;
            }

but it is not I need:

1. I can't unsubscribe if active document is closed. I want to be very accurate here, because, if I understand correctly, subscription without unsubscription carriers a risk of memory leak.
2. I can't resubscribe is active document is opened (I need to poll not-null active document in a background thread).

Could anyone give me a hint?

Thank you!