iphone - position 和 positionInPixels 有什么区别

Question

过去我总是看到名为position 和positionInPixels 的属性是相同的。这次 position * 2 == positionInPixels。谁能告诉我这两个属性之间有什么区别，或者它们的值何时会不同？

Answer 1

position 以点为单位，positionInPixels 以像素为单位。在非视网膜设备上，1 点 = 1 像素。在 iPhone 4/4S 和 New iPad 等 Retina 设备上，1 点 = 2 像素。

根据 iOS Human Interface Guidelines :

Note: Pixel is the appropriate unit of measurement to use when discussing the size of a device screen or the size of an icon you create in an image-editing application. Point is the appropriate unit of measurement to use when discussing the size of an area that is drawn onscreen.

On a standard-resolution device screen, one point equals one pixel, but other resolutions might dictate a different relationship. On a Retina display, for example, one point equals two pixels.

See "Points Versus Pixels" in View Programming Guide for iOS for a complete discussion of this concept.