NS_OPTIONS枚舉的用法

定義:

```objective-c
//NS_OPTIONS，定義選項
typedef NS_OPTIONS(NSUInteger, MyOption) {
MyOptionNone = 0, //二進制0000,十進制0
MyOption1 = 1 << 0,//0001,1
MyOption2 = 1 << 1,//0010,2
MyOption3 = 1 << 2,//0100,4
MyOption4 = 1 << 3,//1000,8
};

##使用:

```objective-c
//聲明定義枚舉變量
MyOption option = MyOption1 | MyOption2;//0001 | 0010 = 0011,3

//檢查是否包含某選型
if ( option & MyOption3 ){ //0011 & 0100 = 0000
     //包含MyOption3
}else{
     //不包含MyOption3
}

//增長選項:
option = option | MyOption4;//0011 | 1000 = 1011, 11
//減小選項
option = option & (~MyOption4);//1011 & (~1000) = 1011 & 0111 = 0011, 3