推荐阅读iPhone核心动画

Can anyone here recommend any good books for getting my head around Core animation? I've been through the Apple docs and while I'm sure it's all there, I haven't been able to grok Core Animation yet... Is there an a good example I've missed? or some starting document I've overlooked? If not are there any good books out there on Core Animation... the few hits I've gotten while looking on Amazon don't rate anything too high, mostly MacOSX little iphone. Thanks in advance for any suggestionsCan anyone here recommend any good books for ge