CATiledLayer tile invalidation

FROM : Dmitry Pugachev
DATE : Mon Mar 24 16:39:55 2008

I'm writing an application that dynamically renders
contents into a large scrollable view, and I'm using
a CATiledLayer object as a content layer.  It handles
tiled drawing pretty well, but I also want to be able
to synchronize it with my internal cache, which contains
temporary data for each tile being rendered.

While I can add content to this internal cache as I
render individual tiles, I can't seem to be able to
invalidate off-sceen portions of the cache when
the corresponding portions of the internal CATiledLayer
image buffer get invalidated.  For example, if I scroll
down continuously, each new tile rendered would
add data to my internal cache, while the old tiles
will never get invalidated.  On the other hand, I want
to be able to keep the cache size under control by
removing old content, just like CATiledLayer does
for its internal image data.

Is there a way to register a callback that will be
invoked by CATiledLayer when it internally
invalidates an outdated portion of its content?

Thanks in advance,
Dmitry