https://blog.csdn.net/daleiwang/article/details/50581872
1.iOS程序中，最好所有的枚举都用“NS_ENUM”和“NS_OPTIONS”定义，保证统一。
//NS_ENUM，定义状态等普通枚举
typedef NS_ENUM(NSUInteger, TTGState) {
TTGStateOK = 0,
TTGStateError,
TTGStateUnknow
};
//NS_OPTIONS，定义选项
typedef NS_OPTIONS(NSUInteger, TTGDirection) {
TTGDirectionNone = 0,
TTGDirectionTop = 1 << 0,
TTGDirectionLeft = 1 << 1,
TTGDirectionRight = 1 << 2,
TTGDirectionBottom = 1 << 3
};
2.熟悉一下位运算
https://www.jianshu.com/p/66bae556483d
