一般情况下我们在开发中可以采用C风格的enum 关键字定义枚举类型
enum{
UIViewAnimationTransitionNone,
UIViewAnimationTransitionFlipFromLeft,
UIViewAnimationTransitionFlipFromRight,
UIViewAnimationTransitionCurlUp,
UIViewAnimationTransitionCurlDown,
}
位移动操作枚举定义
enum {
UIViewAutoresizingNone = 0,
UIViewAutoresizingFlexibleLeftMargin = 1 << 0,
UIViewAutoresizingFlexibleWidth = 1 << 1,
UIViewAutoresizingFlexibleRightMargin = 1 << 2,
UIViewAutoresizingFlexibleTopMargin = 1 << 3,
UIViewAutoresizingFlexibleHeight = 1 << 4,
UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
typedef NSUInteger UIViewAutoresizing;
//使用NSUInteger的地方可以使用UIViewAutoresizing,//UIViewAutoresizing相当于NSUInteger的一个别名使用
//因此一个UIViewAutoresizing的变量可以直接赋值给NSUInteger
枚举值一般是4个字节的int值，在64位系统上是8个字节
typedef NS_ENUM(NSInteger, UIBarButtonItemStyle) {
UIBarButtonItemStylePlain,// 默认从0开始
UIBarButtonItemStyleBordered,
UIBarButtonItemStyleDone,
};
typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
UIViewAutoresizingNone = 0,
UIViewAutoresizingFlexibleLeftMargin = 1 << 0,
UIViewAutoresizingFlexibleWidth = 1 << 1,
UIViewAutoresizingFlexibleRightMargin = 1 << 2,
UIViewAutoresizingFlexibleTopMargin = 1 << 3,
UIViewAutoresizingFlexibleHeight = 1 << 4,
UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
这两个宏的定义在framework的NSObjCRuntime中
包
定义
从枚举定义来看，NS_ENUM和NS_OPTIONS本质是一样的。NS_ENUM是通用情况，NS_OPTIONS一般用来定义具有位移操作或特点的情况
