Martin Hewitson asked this question a little while ago on cocoa-dev:

Does anyone know what messages the delegate of an IKImageView will get? I can't find any documentation or examples.

I was surprised to find there is indeed nothing about this in the docs. I Googled "IKImageView delegate" and the top hit was page 2 of an article posted by Dave Jewell for The Register in 2008. The article lists delegate methods that seem to have been discovered via class-dump.

In 2010 the question was asked again and still not answered in the docs.

I hoped the methods might at least be declared in a header, but the following returns no results:

$ cd /Developer/SDKs/MacOSX10.6.sdk/System/Library/Frameworks/Quartz.framework/Versions/A/Frameworks/ImageKit.framework/Versions/A/Headers/
$ grep imageWillChange *

Apple's own IKImageViewDemo example code sets the delegate but never implements any delegate methods.

Searching StackOverflow does not find anybody asking this question, although there are plenty of other questions about IKImageView.

So here is a class that has been around since 10.5, that people are clearly using, and its delegate has never been documented? Why hasn't there been more of a clamor about this?

If you implement one of the methods listed in Dave Jewell's article, will Apple reject you from the App Store for using an undocumented API?

Jewell wrote:

In fairness to Apple, the lack of documentation is probably due – in part – to the complexity of the ImageKit framework.

I think that's way beyond fair. We all have bugs in our work, whether it's code or documentation, but I would find it odd for someone to excuse a glaring bug of mine out of "fairness".

I just filed rdar://10114629.