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,
};
