NS_OPTIONS

typedef NS_OPTIONS(NSUInteger, UISwipeGestureRecognizerDirection) {
    UISwipeGestureRecognizerDirectionNone = 0,  //值为0
    UISwipeGestureRecognizerDirectionRight = 1 << 0,  //值为2的0次方
    UISwipeGestureRecognizerDirectionLeft = 1 << 1,  //值为2的1次方
    UISwipeGestureRecognizerDirectionUp = 1 << 2,  //值为2的2次方
    UISwipeGestureRecognizerDirectionDown = 1 << 3  //值为2的3次方
};

小括号中第一个为NSUInteger这个为固定值，第二个为枚举类型，自己定义，大括号中枚举项必须全部包含小括号的枚举类型，枚举项后面再跟上几个值的区别，这里枚举项是NSUInteger类型，它的值我已经标记了，看上面注释，当然也可以像下方这样写枚举，但是官方推荐格式为上面那种。

typedef enum {
    UISwipeGestureRecognizerDirectionNone = 0,  //值为0
    UISwipeGestureRecognizerDirectionRight = 1 << 0,  //值为2的0次方
    UISwipeGestureRecognizerDirectionLeft = 1 << 1,  //值为2的1次方
    UISwipeGestureRecognizerDirectionUp = 1 << 2,  //值为2的2次方
    UISwipeGestureRecognizerDirectionDown = 1 << 3  //值为2的3次方
}UISwipeGestureRecognizerDirection;

NS_ENUM

typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = -1,  //值为-1    
    NSWritingDirectionLeftToRight = 0,  //值为0
    NSWritingDirectionRightToLeft = 1  //值为1       
};

小括号中第一个为NSInteger这个为固定值，第二个为枚举类型，自己定义，大括号中枚举项必须包含小括号中自己定义的枚举类型，枚举项自己加后缀以视区别，大括号中的枚举项的值可自定义，若是定义了枚举项其中一项的值后面依次在它的前一项的值上加1，如这样：

typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = 0,  //值为0    
    NSWritingDirectionLeftToRight,  //值为1
    NSWritingDirectionRightToLeft  //值为2       
};
//或者这样
typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = 0,  //值为0    
    NSWritingDirectionLeftToRight = 2,  //值为2
    NSWritingDirectionRightToLeft  //值为3       
};
//若是都不定义值，默认第一项为0，后面依次枚举项的值加1。

当然也可以下方这样写枚举，但是官方不推荐，还是上面格式规范，

typedef enum {
    NSWritingDirectionNatural = -1,  //值为-1    
    NSWritingDirectionLeftToRight = 0,  //值为0
    NSWritingDirectionRightToLeft = 1  //值为1  
}NSWritingDirection;

UISwipeGestureRecognizer *swipeGR = [[UISwipeGestureRecognizer alloc] init]; swipeGR.direction = UISwipeGestureRecognizerDirectionDown | UISwipeGestureRecognizerDirectionLeft | UISwipeGestureRecognizerDirectionRight; 

//这里几个枚举项同时存在表示它的方向同时包含1.向下2.向左3.向右

而NS_ENUM定义的枚举不能几个枚举项同时存在，只能选择其中一项，像这样：

NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
paragraph.baseWritingDirection = NSWritingDirectionNatural;

使用：

typedef NS_OPTIONS(NSInteger, TestType) {
    TestTypeOne   = 1 << 1,  // 0001 --> 0010 = 2
    TestTypeTwo   = 1 << 2,  // 0001 --> 0100 = 4
    TestTypeThree = 1 << 3,  // 0001 --> 1000 = 8
};

TestType type = TestTypeOne | TestTypeTwo; //00000010 + 00000100 = 00000110 -> 6
    if (type & TestTypeOne) {  //00000110 & 00000010 = 00000010 -> 2
        NSLog(@"包含 one");
    }
    if (type & TestTypeTwo) {  //00000110 & 00000100 = 00000100 -> 4
        NSLog(@"包含 two");
    }
    if (type & TestTypeThree) { //00000110 & 00001000 = 00000000 -> 0
        NSLog(@"包含 three");
    }

打印结果：

开发中常用NS_ENUM和NS_OPTIONS来定义枚举，二者有何区别？使用时该如何抉择呢？

总结：只要枚举值需要用到按位或（2个及以上枚举值可多个存在）就使用NS_OPTIONS，否则使用NS_ENUM。

NS_OPTIONS

typedef NS_OPTIONS(NSUInteger, UISwipeGestureRecognizerDirection) {
    UISwipeGestureRecognizerDirectionNone = 0,  //值为0
    UISwipeGestureRecognizerDirectionRight = 1 << 0,  //值为2的0次方
    UISwipeGestureRecognizerDirectionLeft = 1 << 1,  //值为2的1次方
    UISwipeGestureRecognizerDirectionUp = 1 << 2,  //值为2的2次方
    UISwipeGestureRecognizerDirectionDown = 1 << 3  //值为2的3次方
};

typedef enum {
    UISwipeGestureRecognizerDirectionNone = 0,  //值为0
    UISwipeGestureRecognizerDirectionRight = 1 << 0,  //值为2的0次方
    UISwipeGestureRecognizerDirectionLeft = 1 << 1,  //值为2的1次方
    UISwipeGestureRecognizerDirectionUp = 1 << 2,  //值为2的2次方
    UISwipeGestureRecognizerDirectionDown = 1 << 3  //值为2的3次方
}UISwipeGestureRecognizerDirection;

NS_ENUM

typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = -1,  //值为-1    
    NSWritingDirectionLeftToRight = 0,  //值为0
    NSWritingDirectionRightToLeft = 1  //值为1       
};

typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = 0,  //值为0    
    NSWritingDirectionLeftToRight,  //值为1
    NSWritingDirectionRightToLeft  //值为2       
};
//或者这样
typedef NS_ENUM(NSInteger, NSWritingDirection) {
    NSWritingDirectionNatural = 0,  //值为0    
    NSWritingDirectionLeftToRight = 2,  //值为2
    NSWritingDirectionRightToLeft  //值为3       
};
//若是都不定义值，默认第一项为0，后面依次枚举项的值加1。

当然也可以下方这样写枚举，但是官方不推荐，还是上面格式规范，

typedef enum {
    NSWritingDirectionNatural = -1,  //值为-1    
    NSWritingDirectionLeftToRight = 0,  //值为0
    NSWritingDirectionRightToLeft = 1  //值为1  
}NSWritingDirection;

UISwipeGestureRecognizer *swipeGR = [[UISwipeGestureRecognizer alloc] init]; swipeGR.direction = UISwipeGestureRecognizerDirectionDown | UISwipeGestureRecognizerDirectionLeft | UISwipeGestureRecognizerDirectionRight; 

//这里几个枚举项同时存在表示它的方向同时包含1.向下2.向左3.向右

而NS_ENUM定义的枚举不能几个枚举项同时存在，只能选择其中一项，像这样：

NSMutableParagraphStyle *paragraph = [[NSMutableParagraphStyle alloc] init];
paragraph.baseWritingDirection = NSWritingDirectionNatural;

使用：

typedef NS_OPTIONS(NSInteger, TestType) {
    TestTypeOne   = 1 << 1,  // 0001 --> 0010 = 2
    TestTypeTwo   = 1 << 2,  // 0001 --> 0100 = 4
    TestTypeThree = 1 << 3,  // 0001 --> 1000 = 8
};

TestType type = TestTypeOne | TestTypeTwo; //00000010 + 00000100 = 00000110 -> 6
    if (type & TestTypeOne) {  //00000110 & 00000010 = 00000010 -> 2
        NSLog(@"包含 one");
    }
    if (type & TestTypeTwo) {  //00000110 & 00000100 = 00000100 -> 4
        NSLog(@"包含 two");
    }
    if (type & TestTypeThree) { //00000110 & 00001000 = 00000000 -> 0
        NSLog(@"包含 three");
    }

打印结果：