推荐的枚举写法

建议书写枚举模仿苹果——在列出枚举内容的同时绑定了枚举数据类型NSUInteger，这样带来的好处是增强的类型检查和更好的代码可读性,示例:

// 不推荐写法

typedef enum{

UIControlStateNormal = 0,

UIControlStateHighlighted = 1 << 0,

UIControlStateDisabled = 1 << 1,

} UIControlState;

// 推荐写法

typedef NS_OPTIONS(NSUInteger, UIControlState) {

UIControlStateNormal = 0,

UIControlStateHighlighted = 1 << 0,

UIControlStateDisabled = 1 << 1,

};