NSNotificationCenter是使用观察者模式来实现的用于跨层传递消息。
观察者模式
定义对象间的一种一对多的依赖关系。当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并自动更新。
简单的源码样例
注意点：
- 观察者接收到通知后执行任务的代码在发送通知的线程中执行
- 需要先注册监听再发送通知才能正确监听
定义一个观察者model用于保存观察者的各种信息
@interface NTOObserver : NSObject
@property (nonatomic, strong) id observer;
@property (nonatomic, assign) SEL selector;
@property (nonatomic, copy) NSString *notificationName;
@end
NTONotificationCenter对象的实现
@interface NTONotificationCenter : NSObject
+ (NTONotificationCenter *)defaultCenter;
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(nullable NSString *)aName;
- (void)postNotificationName:(NSString *)aName;
@end
@interface NTONotificationCenter ()
@property (nonatomic, strong) NSMutableArray *observers;
@end
@implementation NTONotificationCenter
- (instancetype)init {
if (self = [super init]) {
_observers = [NSMutableArray array];
}
return self;
}
+ (NTONotificationCenter *)defaultCenter {
static NTONotificationCenter *defaultCenter;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
defaultCenter = [[self alloc] init];
});
return defaultCenter;
}
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(NSString *)aName {
NTOObserver *model = [[NTOObserver alloc] init];
model.observer = observer;
model.selector = aSelector;
model.notificationName = aName;
[self.observers addObject:model];
}
- (void)postNotificationName:(NSString *)aName {
[self.observers enumerateObjectsUsingBlock:^(NTOObserver *obj, NSUInteger idx, BOOL * _Nonnull stop) {
if ([aName isEqualToString:obj.notificationName]) {
[obj.observer performSelector:obj.selector];
}
}];
}
