一、简介
像NSArray、NSSet、NSDictionary等集合类均可获取到NSEnumerator, 该类是一个抽象类，没有用来创建实例的公有接口。NSEnumerator的nextObject方法可以遍历每个集合元素，结束返回nil，通过与while结合使用可遍历集合中所有项。
二、使用解析
1、NSArray中使用到的NSEnumerator，代码如下：
- (void)addArrayBtn{
UIButton *btn = [[UIButton alloc]init];
btn.frame = CGRectMake(0, 200, 300, 50);
CGPoint btnCenter = CGPointMake(self.view.center.x, btn.frame.origin.y + 25);
btn.center = btnCenter;
btn.backgroundColor = [UIColor orangeColor];
[self.view addSubview:btn];
[btn setTitle:@"NSArray中NSEnumerator用法" forState:UIControlStateNormal];
[btn addTarget:self action:@selector(didClickArrayBtn) forControlEvents:UIControlEventTouchUpInside];
}
- (void)didClickArrayBtn{
/*
- (NSEnumerator<ObjectType> *)objectEnumerator; //正向遍历数组
- (NSEnumerator<ObjectType> *)reverseObjectEnumerator;//反向遍历数组
*/
NSArray *array = @[@"hehe",@"xixi",@"heihei",@"wuwu",@"lala",@"haha"];
NSEnumerator *enumerator = [array objectEnumerator];
NSString *obj;
while (obj = [enumerator nextObject]) {
NSLog(@"数组正序值开始打印：%@\n",obj);
}
NSEnumerator *reverseEnumerator = [array reverseObjectEnumerator];
id reverseObj;
while (reverseObj = [reverseEnumerator nextObject]) {
NSLog(@"数组逆序值开始打印：%@\n",reverseObj);
}
}
2、NSDictionary中NSEnumerator的使用，代码如下：
- (void)addDictionaryBtn{
UIButton *btn = [[UIButton alloc]init];
btn.frame = CGRectMake(0, 300, 300, 50);
CGPoint btnCenter = CGPointMake(self.view.center.x, btn.frame.origin.y + 25);
btn.center = btnCenter;
btn.backgroundColor = [UIColor orangeColor];
[self.view addSubview:btn];
[btn setTitle:@"NSDictionary中NSEnumerator用法" forState:UIControlStateNormal];
[btn addTarget:self action:@selector(didClickDictionaryBtn) forControlEvents:UIControlEventTouchUpInside];
}
- (void)didClickDictionaryBtn{
/*
- (NSEnumerator<KeyType> *)keyEnumerator;//获取所有key值
- (NSEnumerator<ObjectType> *)objectEnumerator;//获取所有value值
*/
NSDictionary *dict = @{@"name":@"zhangsan",@"age":@(18),@"height":@(173.5)};
NSEnumerator *keyEnumerator = [dict keyEnumerator];
NSString *key;
while (key = [keyEnumerator nextObject]) {
NSLog(@"字典key值开始打印：%@\n",key);
}
NSEnumerator *objEnumerator = [dict objectEnumerator];
id obj;
while (obj = [objEnumerator nextObject]) {
NSLog(@"字典value值开始打印：%@\n",obj);
}
}
3、NSSet中NSEnumerator的使用，代码如下：
- (void)addSetBtn{
UIButton *btn = [[UIButton alloc]init];
btn.frame = CGRectMake(0, 400, 300, 50);
CGPoint btnCenter = CGPointMake(self.view.center.x, btn.frame.origin.y + 25);
btn.center = btnCenter;
btn.backgroundColor = [UIColor orangeColor];
[self.view addSubview:btn];
[btn setTitle:@"NSSet中NSEnumerator用法" forState:UIControlStateNormal];
[btn addTarget:self action:@selector(didClickSetBtn) forControlEvents:UIControlEventTouchUpInside];
}
- (void)didClickSetBtn{
/*
- (NSEnumerator<ObjectType> *)objectEnumerator; //获取所有元素的值，并且是无序的
*/
NSSet *set = [[NSSet alloc]initWithObjects:@"hehe",@"xixi",@"heihei",@"wuwu",@"lala",@"haha",nil];
NSEnumerator *enumerator = [set objectEnumerator];
id obj;
while (obj = [enumerator nextObject]) {
NSLog(@"NSSet中value值开始打印：%@\n",obj);
}
}
4、看打印效果，在ViewController中添加这三个Btn即可点击后打印：
代码：
- (void)viewDidLoad {
[super viewDidLoad];
[self addArrayBtn];
[self addDictionaryBtn];
[self addSetBtn];
}
打印效果：
Snip20170505_70.png
三、其他扩展
1、针对于NSEnumerator这个类文件相关内容如下
typedef struct {
unsigned long state;
id __unsafe_unretained _Nullable * _Nullable itemsPtr;
unsigned long * _Nullable mutationsPtr;
unsigned long extra[5];
} NSFastEnumerationState;
@protocol NSFastEnumeration
- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id __unsafe_unretained _Nullable [_Nonnull])buffer count:(NSUInteger)len;
@end
@interface NSEnumerator<ObjectType> : NSObject <NSFastEnumeration>
- (nullable ObjectType)nextObject;
@end
@interface NSEnumerator<ObjectType> (NSExtendedEnumerator)
@property (readonly, copy) NSArray<ObjectType> *allObjects;
@end
其中有一个协议NSFastEnumeration，实现这个协议的方法就可以实现快速遍历，集合类都遵守了此协议，所以集合都能够实现快速遍历，具体该怎么使用请看贴文
