For many purposes you can avoid needing this functionality
completely with a little thought. For instance, say you're
displaying files to the user (like Finder does). In that case, a
good technique is to refresh your view every time the user
activates your window. That way, if they switch to another app and
save something, you're guaranteed to notice it at just the right time.
God no, please don't take the 10.0 Finder's approach ... it has
issues:
1) A user may be waiting for the download to finish with your window
open, then decide to play a round of Mine S^H^H^H Solit^H^H^H Chess,
glancing over at your background window occasionally to see whether
the download's finished. If you don't update until it's activated,
your window will not update correctly.
2) #1 can even apply in your application, if you have several windows
open, the non-current ones will not update.
3) This is only possible if your view will already be open. With an
app like Hazel, that generally watches your folders in the
background, that won't work.
4) This can lead to big confusion: Imagine the user double-clicks in
an inactive window. This activates your window and updates its
contents, inserting a new file in the list above the entry you double-
clicked. Suddenly your list item has moved, and you end up opening
the wrong file. This can also happen with live updates, but generally
the user does something to cause a file system change (in another app
or another window), so at the moment your window updates, the user
will be looking elsewhere. OTOH, if your window updates as it's
activated, you're coalescing all changes towards the point where the
user is actually interested in and about to use your window.
In short: You'll just end up annoying your users. Use real file
system notifications like kqueues, or use polling and only update a
little *after* window activation (performSelector:withDelay: is your
friend), and only after a bit of user-idleness. Just try opening a
smart folder in Finder that contains lots of items from a slow disk.
Stuff will constantly be moving around and therefore you can't click
anything until all items have been loaded, even if your item of
interest was loaded as the fifth one.
