iOS 枚舉講解

時間  2019-11-18
標籤 ios 枚舉 講解 欄目 iOS 简体版
原文   原文鏈接

枚舉加強程序的可讀性，用法上仍是須要注意的app

1.C語言的寫法

enum XMPPReconnectFlags
{
 kShouldReconnect   = 1 << 0,  // If set, disconnection was accidental, and autoReconnect may be used
 kMultipleChanges   = 1 << 1,  // If set, there have been reachability changes during a connection attempt
 kManuallyStarted   = 1 << 2,  // If set, we were started manually via manualStart method
 kQueryingDelegates = 1 << 3,  // If set, we are awaiting response(s) from the delegate(s)
};

或者是ide

typedef enum XMPPReconnectFlags
{
 kShouldReconnect   = 1 << 0,  // If set, disconnection was accidental, and autoReconnect may be used
 kMultipleChanges   = 1 << 1,  // If set, there have been reachability changes during a connection attempt
 kManuallyStarted   = 1 << 2,  // If set, we were started manually via manualStart method
 kQueryingDelegates = 1 << 3,  // If set, we are awaiting response(s) from the delegate(s)
}XMPPReconnectFlags;//此處的XMPPReconnectFlags爲別名

2.OC的寫法

typedef NS_ENUM(NSInteger, XMPPMessageBodyType) {
    XMPPMessageBodyTypeText = 1,       //文本
    XMPPMessageBodyTypeImage,          //圖片
    XMPPMessageBodyTypeSound,          //語音
    XMPPMessageBodyTypeMap,            //地理信息（文本）
    XMPPMessageBodyTypeNotification,   //通知
    XMPPMessageBodyTypeCustom,         //自定義
    XMPPMessageBodyTypeVideo,          //視頻
    XMPPMessageBodyTypeExpression,     //表情
};

第一個枚舉值只要NSInteger類型，後面的依次累加，中間再從新賦值，後面的會從賦值處從新累加this

3.NS_ENUM和NS_OPTIONS

NS_ENUM和NS_OPTIONS本質是同樣的，僅僅從字面上來區分其用途。NS_ENUM是通用狀況，NS_OPTIONS通常用來定義具備位移操做或特色的狀況lua

typedef NS_OPTIONS(NSInteger, ShareViewItemType) {
    ShareViewItemTypeWX = 1,
    ShareViewItemTypeWXFC = 1 << 0,
    ShareViewItemTypeQQ= 1 << 1,
    ShareViewItemTypeWB= 1 << 1,
    ShareViewItemTypeReport= 1 << 3,
    ShareViewItemTypeBarrage = 1 << 4,
    ShareViewItemTypeAll = 1 << 5,
};

若是多選枚舉，那麼須要這樣判斷spa

+ (instancetype)shareViewWithDic:(NSDictionary*)dic shareViewItemType:(ShareViewItemType)shareViewItemType;
{
    if (shareViewItemType == (ShareViewItemTypeWX|ShareViewItemTypeWXFC)) {
        // code
    }
}

4.官方的全選枚舉

UIControl的枚舉code

typedef NS_OPTIONS(NSUInteger, UIControlEvents) {
    UIControlEventTouchDown                                         = 1 <<  0,      // on all touch downs
    UIControlEventTouchDownRepeat                                   = 1 <<  1,      // on multiple touchdowns (tap count > 1)
    UIControlEventTouchDragInside                                   = 1 <<  2,
    UIControlEventTouchDragOutside                                  = 1 <<  3,
    UIControlEventTouchDragEnter                                    = 1 <<  4,
    UIControlEventTouchDragExit                                     = 1 <<  5,
    UIControlEventTouchUpInside                                     = 1 <<  6,
    UIControlEventTouchUpOutside                                    = 1 <<  7,
    UIControlEventTouchCancel                                       = 1 <<  8,

    UIControlEventValueChanged                                      = 1 << 12,     // sliders, etc.
    UIControlEventPrimaryActionTriggered NS_ENUM_AVAILABLE_IOS(9_0) = 1 << 13,     // semantic action: for buttons, etc.

    UIControlEventEditingDidBegin                                   = 1 << 16,     // UITextField
    UIControlEventEditingChanged                                    = 1 << 17,
    UIControlEventEditingDidEnd                                     = 1 << 18,
    UIControlEventEditingDidEndOnExit                               = 1 << 19,     // 'return key' ending editing

    UIControlEventAllTouchEvents                                    = 0x00000FFF,  // for touch events
    UIControlEventAllEditingEvents                                  = 0x000F0000,  // for UITextField
    UIControlEventApplicationReserved                               = 0x0F000000,  // range available for application use
    UIControlEventSystemReserved                                    = 0xF0000000,  // range reserved for internal framework use
    UIControlEventAllEvents                                         = 0xFFFFFFFF
};

最後一個 UIControlEventAllEvents賦值爲0xFFFFFFFF，意爲全選，實際工程使用沒有問題，很方便，可是在
Archive的時候會報錯orm


屏幕快照 2016-06-29 下午12.28.10.png


這個地方須要這樣改視頻

typedef NS_OPTIONS(NSUInteger, ShareViewItemType) {
    ShareViewItemTypeWX = 1,
    ShareViewItemTypeWXFC = 1 << 0,
    ShareViewItemTypeQQ= 1 << 1,
    ShareViewItemTypeWB= 1 << 1,
    ShareViewItemTypeReport= 1 << 3,
    ShareViewItemTypeBarrage = 1 << 4,
    ShareViewItemTypeAll = 0xFFFFFFFF,
};

你能夠這樣判斷條件blog

+ (instancetype)shareViewWithDic:(NSDictionary*)dic shareViewItemType:(ShareViewItemType)shareViewItemType;
{
// 入參shareViewItemType爲ShareViewItemTypeAll
    if (shareViewItemType & ShareViewItemTypeBarrage) {
        // code
    }
}

5.使用層面的理解

在這裏首先講如何簡單的使用, 僅僅是使用層面(有理解錯誤的地方幫忙糾正), 而後咱們在去理解位運算符! 在下面的圖中咱們能夠看見枚舉值中有<<(位運算符:左移):事件


 

若是咱們在枚舉值中看見<<那咱們就能夠經過|(位運算符:或)進行組合使用以下代碼爲例:

//隨便添加一個UITextField
 UITextField *field = [UITextField new];
 //Begin,Changed,DidEnd都能觸發UITextField的事件
 [field addTarget:self action:@selector(textFieldDidChanged) forControlEvents: UIControlEventEditingDidBegin |
                  UIControlEventValueChanged |
                  UIControlEventEditingDidEnd
     ];

 [self.view addSubview:field];

以下圖枚舉值中沒有<<,這就是普通的NSInteger類型的枚舉, 因此不能組合使用:


 

那蘋果官方是怎麼知道咱們多個條件組合使用了呢? 答案是經過&(位運算符:與)進行判斷的:

//controlEvents是組合使用後的一個值
 NSUInteger controlEvents = UIControlEventEditingDidBegin | UIControlEventValueChanged | UIControlEventEditingDidEnd;
    /**
    //經過 & 來判斷是否包含:
    UIControlEventEditingDidBegin,
    UIControlEventValueChanged,
    UIControlEventEditingDidEnd
     */
    if (controlEvents & UIControlEventEditingDidBegin) {

        NSLog(@"UIControlEventEditingDidBegin");

    }else if (controlEvents & UIControlEventValueChanged) {

        NSLog(@"UIControlEventValueChanged");

    }else if (controlEvents & UIControlEventEditingDidEnd) {

        NSLog(@"UIControlEventEditingDidEnd");
    }

那麼咱們接下來看看使用過程當中牽扯到的位運算符, 咱們會在下面舉個例子!

6.理解位運算符

首先咱們有一個枚舉, 下面代碼2種寫法咱們暫時先不用管,等位運算符講完咱們會討論枚舉的宏使用:

//typedef NS_OPTIONS(NSInteger, myTests) {
//    nameA = 1 << 0,
//    nameB = 1 << 1,
//    nameC = 1 << 2,
//    nameD = 1 << 3,
//};

typedef enum {
    nameA = 1 << 0,
    nameB = 1 << 1,
    nameC = 1 << 2,
    nameD = 1 << 3,

}myTests;

/**
 nameA = 1 << 0 :值爲1(2的0次方)
 nameB = 1 << 1 :值爲2(2的1次方)
 nameC = 1 << 2 :值爲4(2的2次方)
 nameD = 1 << 3 :值爲8(2的3次方)
 */

經過&進行判斷咱們來看看輸出結果以下圖:


 

咱們獲得NSInteger value = nameA | nameB;的組合的值, 判斷結果是:1是nameA的值, 2是nameB的值, nameC與nameD沒有組合使用因此值爲0,最後咱們知道若是value & nameC爲0說明value不包含nameC 相反則包含!

還有一點就是value & nameA就是nameA的值爲1, value & nameB就是nameB的值爲2

  • <<(左移):a << b就表示把a轉爲二進制後左移b位（在後面添b個0）
  • |(或):只要有一個爲1, 結果就是1
  • &(與):只要有二個爲1, 結果纔是1

咱們已經知道nameA = 1, nameB = 2, nameC = 4, nameD = 8下面來經過二進制來解釋:

NSInteger value = nameA | nameB | nameC | nameD;
     轉成二進制:
     nameA: 0 0 0 1
       |
     nameB: 0 0 1 0
       |
     nameC: 0 1 0 0
       |
     nameD: 1 0 0 0
    ----------------
     value: 1 1 1 1
     上面是使用 | 得出value的值爲1111(|的意思是有一個爲1結果就爲1)


     下面是使用 & 判斷輸出的值(&的意思就是有二個爲1結果才爲1)

      value: 1 1 1 1         value: 1 1 1 1
        &                      &
      nameA: 0 0 0 1         nameB: 0 0 1 0
     ----------------       ----------------
      結果值: 0 0 0 1         結果值: 0 0 1 0

      我就寫2個例子:0001就是nameA的值, 0010就是nameB的值

相信你們已經明白其中的道理了, 接下來咱們來看看枚舉的宏, 爲了更好閱讀也能夠看下面的截圖:


 

7.枚舉的宏(NS_ENUM與NS_OPTIONS)

NS_ENUM和NS_OPTIONS宏提供了一個簡潔、定義枚舉和C語言選項的簡單方法。

The NS_ENUM and NS_OPTIONS macros provide a concise, simple way of defining enumerations and options in C-based languages. These macros improve code completion in Xcode and explicitly specify the type and size of your enumerations and options. Additionally, this syntax declares enums in a way that is evaluated correctly by older compilers, and by newer ones that can interpret the underlying type information.

這是最初的使用方法:

enum {
        UITableViewCellStyleDefault,
        UITableViewCellStyleValue1,
        UITableViewCellStyleValue2,
        UITableViewCellStyleSubtitle
};
typedef NSInteger UITableViewCellStyle;

--------------------------------------------------

enum {
        UIViewAutoresizingNone                 = 0,
        UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
        UIViewAutoresizingFlexibleWidth        = 1 << 1,
        UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
        UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
        UIViewAutoresizingFlexibleHeight       = 1 << 4,
        UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
typedef NSUInteger UIViewAutoresizing;

經過使用枚舉的宏:

NS_ENUM:是用來聲明通常的NSInteger(下面代碼使用NSInteger)類型的枚舉

Use the NS_ENUM macro to define enumerations, a set of values that are mutually exclusive.

NS_OPTIONS:是用來聲明位掩碼(bitmasked)

Use the NS_OPTIONS macro to define options, a set of bitmasked values that may be combined together.

//NS_ENUM
typedef NS_ENUM(NSInteger, UITableViewCellStyle) {
        UITableViewCellStyleDefault,
        UITableViewCellStyleValue1,
        UITableViewCellStyleValue2,
        UITableViewCellStyleSubtitle
};

--------------------------------------------------

//NS_OPTIONS
typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
        UIViewAutoresizingNone                 = 0,
        UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
        UIViewAutoresizingFlexibleWidth        = 1 << 1,
        UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
        UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
        UIViewAutoresizingFlexibleHeight       = 1 << 4,
        UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};

NS_OPTIONS 與 NS_ENUM 和 enum 是有什麼區別呢?

1.經過上面介紹咱們能夠看出enum能夠聲明通常類型和位掩碼(bitmasked)類型

2.NS_ENUM聲明通常類型, NS_OPTIONS聲明掩碼(bitmasked)類型

3.那麼問題又來了, 直接用enum不就能夠了? 答案不是這樣的, 蘋果建議咱們在OC中使用NS_ENUM與NS_OPTIONS, 爲何呢? 由於他們除了推斷出不一樣類型的枚舉,再就是當編譯Objective-C++模式，它們產生的代碼是不一樣的, 就是由於不一樣因此混編的時候使用enum會報錯!

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