判断当前设备类型

//判断是不是高清屏幕
#define isRetina ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 960), [[UIScreen mainScreen] currentMode].size) : NO)

//判断是不是iPad
#define isPad (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)

//判断是不是模拟器
#define isSimulator (NSNotFound != [[[UIDevice currentDevice] model] rangeOfString:@"Simulator"].location)