iOS-枚举

枚举的作用：增强代码的可读性，
1.C语言的写法

enum LJCPPReconnectFlags
{
    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)
};

2.OC中有两种写法

1、typedef NS_ENUM(NSInteger, ****Type) 模式, 第一个枚举值只要NSInteger类型，后面的依次累加，中间再重新赋值，后面的会从赋值处重新累加

typedef NS_ENUM(NSInteger, LJCMessageBodyType) {
    LJCMessageBodyTypeText = 1,       //文本
    LJCMessageBodyTypeImage,          //图片
    LJCMessageBodyTypeSound,          //语音
    LJCMessageBodyTypeMap,            //地理信息（文本）
    LJCMessageBodyTypeNotification,   //通知
    LJCMessageBodyTypeCustom,         //自定义
    LJCMessageBodyTypeVideo,          //视频
    LJCMessageBodyTypeExpression,     //表情
};

2、typedef NS_OPTIONS(NSInteger, *****Type) 模式, 具有位移操作，

typedef NS_OPTIONS(NSUInteger, LJCType) {
    LJCTypeWX = 1,
    LJCTypeWXFC = 1 << 0,
    LJCTypeQQ= 1 << 1,
    LJCTypeWB= 1 << 1,
    LJCTypeReport= 1 << 3,
    LJCTypeBarrage = 1 << 4,
    LJCTypeAll = 0xFFFFFFFF,
};

<<(左移):a << b就表示把a转为二进制后左移b位（在后面添b个0）

LJCTypeAll = 0xFFFFFFFF 表示全选

如果我们在枚举值中看见<<那我们就可以通过|(位运算符:或)进行组合使用如下代码为例:

//随便添加一个UITextField
UITextField *field = [UITextField new];
//Begin,Changed,DidEnd都能触发UITextField的事件
[field addTarget:self action:@selector(textFieldDidChanged) forControlEvents: UIControlEventEditingDidBegin |
                  UIControlEventValueChanged |
                  UIControlEventEditingDidEnd
     ];
[self.view addSubview:field];