判断iphone的屏幕是不是retina屏幕

#define isRetina ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 960), [[UIScreen mainScreen] currentMode].size) : NO)

转载于:https://www.cnblogs.com/zhourh/archive/2012/05/02/2479046.html