问题
Does anyone know how to use core graphics to draw a pdf like in iBooks. I can already draw a pdf page using core graphics but was curious how iBooks shows a lower quality view of each page so it loads fast and then when you stay on a page longer it renders it a full quality. This makes it able to open the pdf without having to make the user wait like most magazine apps you see on ipad. Any ideas would help!
回答1:
Apple have some "ZoomingPDFViewer" sample code:
http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010281
I suspect that might give you some good ideas :-)
回答2:
I assume they use multiple layers, the first layer loads the pdf in low resolution and the better resolution is prepared in the background. When ready these layers are swapped.
Have a look at CGPDFDocumentRef and CATiledLayer in the documentation.
来源：https://stackoverflow.com/questions/3810536/iphone-ipad-draw-pdf-like-ibooks