ZoomingPDFViewer apple example

I'm trying to understand Apple's example code for the ZoomingPDFViewer. Here are some questions that I have in my understanding of how it works in my mind. I'm not really sure if I understand it correctly. The link for their code is at: http://developer.apple.com/library/ios/#samplecode/ZoomingPDFViewer/Introduction/Intro.html

(1) CATiledLayer is used to represent the PDF at different zoom levels. I'm assuming that's what this class is used for looking at the Class Reference. Would you ever use something else besides this class for a zooming function?

(2) in the initWithFrame for TiledPDFView, they do: tiledLayer.tileSize = CGSizeMake(512.0, 512.0); Is the tileSize the tiles that make up for the whole image? If so, w开发者_高级运维hy such a large size?

(3) How does the oldPDFView and pdfView work? Like which one is in front at the different stages of zoom, and when do they get swapped out. I'm having a hard time understanding the flow of the logic. Thanks.

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(1) If you don't require the level of detail to vary for different zoom levels, or if the PDF loads fast enough to not warrant drawing a couple of tiles at a time, a regular UIView with a regular CALayer will work fine. For instance, if you were displaying an image instead of a PDF, and the image loads fast enough to not cause a performance snag, you would not need the asynchronous loading that CATiledLayer provides. The PhotoScroller sample uses both the tiled and non-tiled approaches if you want to compare them.

(2) The tileSize attribute changes the size of the blocks the layer should be split into. You can set this to whatever you want. 512x512 really isn't all that large, especially if your PDF dimensions are big. The default is 256x256.

(3) Anytime you start to zoom, oldPDFView is removed and released. Then pdfView is assigned to oldPDFView. When the zooming ends, a new pdfView is created with the change in scale and added on top of the old one. If the new scale is an increase, the new pdfView will be drawn with a higher level of detail. This makes it so you can zoom deeper and deeper into the PDF. The maximumZoomScale and minimumZoomScale only restrict how much you can zoom with an individual gesture.