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enum

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了解位移枚舉之前，我們先回顧一下C語言位運算符。

1? ? ?<<?:?左移,比如1<<n,表示1往左移n位，即數值大小2的n次方;?例如?:?0b0001?<<?1?變為了?0b0010

2? ? ?>>?:?右移,類似左移,數值大小除以2的n次方
3? ? ?&? :?按位與,1與任意數等于任意數本身,0與任意數等于0,即1&x=x,0&x=0
4? ? ?|? :?按位或,x|y中只要有一個1則結果為1；反之為0
5? ? ?^? :?按位異或,x^y相等則為0,不等則為1

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typedef enum A {
??? a = 0,
??? b,
??? c,
??? d,
} englishWord;

typedef enum {
??? e = 4,
??? f,
??? g,
} englishWord2;

englishWord eg1 = a;
englishWord2 eg2 = e;

// enum newNum:NSInteger枚舉變量，并且繼承NSInteger;englishWord3 枚舉的別名
typedef enum newNum:NSInteger englishWord3;
enum newNum:NSInteger {
??? new1 = 10,
??? new2,
};
englishWord3 eg3 = new1;

eg1 = 0,eg2 = 4, eg3 = 10

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2、NS_ENUM 、NS_OPTIONS

OC中常見的枚舉，例如常見的：

typedef NS_ENUM(NSInteger, UIViewAnimationCurve) {

UIViewAnimationCurveEaseInOut,???????? // slow at beginning and end

UIViewAnimationCurveEaseIn,??????????? // slow at beginning

UIViewAnimationCurveEaseOut,?????????? // slow at end

UIViewAnimationCurveLinear

};

typedef NS_OPTIONS(NSUInteger, UIViewAnimationOptions) {

UIViewAnimationOptionLayoutSubviews??????????? = 1 <<? 0,

UIViewAnimationOptionAllowUserInteraction????? = 1 <<? 1, // turn on user interaction while animating

UIViewAnimationOptionBeginFromCurrentState???? = 1 <<? 2, // start all views from current value, not initial value

UIViewAnimationOptionRepeat??????????????????? = 1 <<? 3, // repeat animation indefinitely

UIViewAnimationOptionAutoreverse?????????????? = 1 <<? 4, // if repeat, run animation back and forth

UIViewAnimationOptionOverrideInheritedDuration = 1 <<? 5, // ignore nested duration

UIViewAnimationOptionOverrideInheritedCurve??? = 1 <<? 6, // ignore nested curve

UIViewAnimationOptionAllowAnimatedContent????? = 1 <<? 7, // animate contents (applies to transitions only)

UIViewAnimationOptionShowHideTransitionViews?? = 1 <<? 8, // flip to/from hidden state instead of adding/removing

UIViewAnimationOptionOverrideInheritedOptions? = 1 <<? 9, // do not inherit any options or animation type

UIViewAnimationOptionCurveEaseInOut??????????? = 0 << 16, // default

UIViewAnimationOptionCurveEaseIn?????????????? = 1 << 16,

UIViewAnimationOptionCurveEaseOut????????????? = 2 << 16,

UIViewAnimationOptionCurveLinear?????????????? = 3 << 16,

UIViewAnimationOptionTransitionNone??????????? = 0 << 20, // default

UIViewAnimationOptionTransitionFlipFromLeft??? = 1 << 20,

UIViewAnimationOptionTransitionFlipFromRight?? = 2 << 20,

UIViewAnimationOptionTransitionCurlUp????????? = 3 << 20,

UIViewAnimationOptionTransitionCurlDown??????? = 4 << 20,

UIViewAnimationOptionTransitionCrossDissolve?? = 5 << 20,

UIViewAnimationOptionTransitionFlipFromTop???? = 6 << 20,

UIViewAnimationOptionTransitionFlipFromBottom? = 7 << 20,

} NS_ENUM_AVAILABLE_IOS(4_0);

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這兩個宏的定義在Foundation.framework的NSObjCRuntime.h中：

#if (__cplusplus && __cplusplus >= 201103L && (__has_extension(cxx_strong_enums) || __has_feature(objc_fixed_enum))) || (!__cplusplus && __has_feature(objc_fixed_enum))

#define NS_ENUM(_type, _name) enum _name : _type _name; enum _name : _type

#if (__cplusplus)

#define NS_OPTIONS(_type, _name) _type _name; enum : _type

#else

#define NS_OPTIONS(_type, _name) enum _name : _type _name; enum _name : _type

#endif

#else

#define NS_ENUM(_type, _name) _type _name; enum

#define NS_OPTIONS(_type, _name) _type _name; enum

#endif

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?

typedef?NS_ENUM（NSInteger,?UIViewAnimationTransition)?{

展開得到：

typedef?enum?UIViewAnimationTransition?:?NSInteger?UIViewAnimationTransition;??

enum?UIViewAnimationTransition?:?NSInteger?{

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其實從枚舉定義來看，NS_ENUM和NS_OPTIONS本質是一樣的，僅僅從字面上來區分其用途。NS_ENUM是通用情況，NS_OPTIONS一般用來定義具有位移操作或特點的情況（bitmask)。

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開發中，你也許見到過或用過類似這種的枚舉類型：

typedef?NS_OPTIONS(NSUInteger,?BDRequestOptions)?{

? ? BDRequestOptionSuccess? ? ?=?1?<<?0,
? ? BDRequestOptionFailure? ? ?=?1?<<?1,
? ? BDRequestOptionProcessing? =?1?<<?2,
? ? BDRequestOptionAnimate? ? ?=?1?<<?3,
};

其實這種的并不是枚舉，而是按位掩碼(bitmask),他的語法和枚舉相同。但用法卻不同。

示例：

// 首先定義一組 typedef NS_OPTIONS(NSUInteger, BDRequestOptions) {BDRequestOptionSuccess = 1 << 0,BDRequestOptionFailure = 1 << 1,BDRequestOptionProcessing = 1 << 2,BDRequestOptionAnimate = 1 << 3, };// 然后調用我們定義的方法 #pragma mark - View lifeCycle - (void)viewDidLoad {[super viewDidLoad];self.view.backgroundColor = [UIColor orangeColor];[self test:BDRequestOptionSuccess | BDRequestOptionFailure | BDRequestOptionProcessing | BDRequestOptionAnimate]; }- (void)test:(BDRequestOptions)type {if (type & BDRequestOptionSuccess) {NSLog(@"BDRequestOptionSuccess");}if (type & BDRequestOptionFailure) {NSLog(@"BDRequestOptionFailure");}if (type & BDRequestOptionProcessing) {NSLog(@"BDRequestOptionProcessing");}if (type & BDRequestOptionAnimate) {NSLog(@"BDRequestOptionAnimate");} }// 查看打印結果: 2016-04-04 14:09:44.946 OC測試[5869:719056] BDRequestOptionSuccess 2016-04-04 14:09:44.947 OC測試[5869:719056] BDRequestOptionFailure 2016-04-04 14:09:44.947 OC測試[5869:719056] BDRequestOptionProcessing 2016-04-04 14:09:44.947 OC測試[5869:719056] BDRequestOptionAnimate

分析：

// 首先定義一組 typedef NS_OPTIONS(NSUInteger, BDRequestOptions) {BDRequestOptionSuccess = 0b0001 << 0,BDRequestOptionFailure = 0b0010 << 1,BDRequestOptionProcessing = 0b0100 << 2,BDRequestOptionAnimate = 0b1000 << 3, };#pragma mark - View lifeCycle - (void)viewDidLoad {[super viewDidLoad];self.view.backgroundColor = [UIColor orangeColor];[self test:BDRequestOptionSuccess | BDRequestOptionFailure | BDRequestOptionProcessing | BDRequestOptionAnimate];/** BDRequestOptionSuccess | BDRequestOptionFailure | BDRequestOptionProcessing | BDRequestOptionAnimate等同于:0b0001 |0b0010 |0b0100 |0b1000 結果為:0b1111*/ }- (void)test:(BDRequestOptions)type {// 0b1111 & 0b0001 ---> 0b0b0001if (type & BDRequestOptionSuccess) {NSLog(@"BDRequestOptionSuccess");}// 0b1111 & 0b0010 ---> 0b0b0010if (type & BDRequestOptionFailure) {NSLog(@"BDRequestOptionFailure");}// 0b1111 & 0b0100 ---> 0b0b0100if (type & BDRequestOptionProcessing) {NSLog(@"BDRequestOptionProcessing");}// 0b1111 & 0b1000 ---> 0b0b1000if (type & BDRequestOptionAnimate) {NSLog(@"BDRequestOptionAnimate");} }

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另，默認的，如果開發中枚舉值傳0，意味著不做任何操作。

例如:

// 傳0，不打印任何值 [self test:0];

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OC中的用法：

NSString *string = @"Learning";[string boundingRectWithSize:CGSizeMake(CGRectGetWidth(self.view.frame), MAXFLOAT)options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingTruncatesLastVisibleLineattributes:@{NSFontAttributeName : [UIFont systemFontOfSize:12.f]}context:nil];

上面傳值：NSStringDrawingUsesLineFragmentOrigin |?NSStringDrawingTruncatesLastVisibleLine

邏輯處理：

1 // 對傳入的option邏輯處理 2 if (option & NSStringDrawingUsesLineFragmentOrigin) { 3 // 包含 NSStringDrawingUsesLineFragmentOrigin 4 } else { 5 // 未包含 NSStringDrawingUsesLineFragmentOrigin 6 } 7 if (option & NSStringDrawingTruncatesLastVisibleLine) { 8 // 包含 NSStringDrawingTruncatesLastVisibleLine 9 } else { 10 // 未包含 NSStringDrawingTruncatesLastVisibleLine 11 }

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對于位移枚舉的具體使用方法，建議可以查看一些三方庫，例如SDWebImage等！

轉載于:https://my.oschina.net/u/2320280/blog/729447

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