How can i save version before filesystemWatcher event?

I have a task to save versions of documents for specified开发者_如何学C directory and look for changes.

before each change i need to keep the CURRENT version of the file in other place.

but the filesystemWatcher doesnt help me here because its events is after the change...

what should i do ?

You'd want to snapshot the target directories before watching them, like when your service starts up or something, that way when the file change comes through you have the base to compare to.