Objective-C的通知是负责对象之间的通信，可以在NSNotificationCenter中注册观察对象，对象也可以NSNotificationCenter发送消息通知.发送对象和接收对象是一对多的关系，通知算是多播(multiCast)形式的一种，如果是向非特定的多个对象发送消息称之为广播(broadcast).
同步 or 异步
通知的注册和发送都是在NSNotificationCenter中实现的，注册观察者，发送消息，还有非常重要的对象销毁的时候注意移除通知.
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(nullable NSNotificationName)aName object:(nullable id)anObject;
#endif
- (void)postNotification:(NSNotification *)notification;
- (void)postNotificationName:(NSNotificationName)aName object:(nullable id)anObject;
- (void)postNotificationName:(NSNotificationName)aName object:(nullable id)anObject userInfo:(nullable NSDictionary *)aUserInfo;
- (void)removeObserver:(id)observer;
- (void)removeObserver:(id)observer name:(nullable NSNotificationName)aName object:(nullable id)anObject;
- (id )addObserverForName:(nullable NSNotificationName)name object:(nullable id)obj queue:(nullable NSOperationQueue *)queue usingBlock:(void (^)(NSNotification *note))block NS_AVAILABLE(10_6, 4_0);
// The return value is retained by the system, and should be held onto by the caller in
// order to remove the observer with removeObserver: later, to stop observation.
注册观察者:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData1:) name:@"updateData" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData2:) name:@"updateData" object:nil];
发送通知:
[[NSNotificationCenter defaultCenter] postNotificationName:@"updateData" object:@{@"age":@"27"} userInfo:@{@"name":@"FlyElephant"}];
收到通知:
- (void)updateData1:(NSNotification *)notificaton {
sleep(1);
NSLog(@"收到通知1---%@",notificaton);
}
- (void)updateData2:(NSNotification *)notificaton {
NSLog(@"收到通知2---%@",notificaton);
}
执行结果:
收到通知1---NSConcreteNotification 0x60800004fc90 {name = updateData; object = {
age = 27;
}; userInfo = {
name = FlyElephant;
}}
收到通知2---NSConcreteNotification 0x60800004fc90 {name = updateData; object = {
age = 27;
}; userInfo = {
name = FlyElephant;
}}
FENotification[3959:7759128] 通知执行完成
调用通知的方法时，所有相关的观察者都会被有序的发送通知消息，是一个同步的过程，我们可以在收到消息之后异步执行代码，通知如果是在子线程中发出，主线程也会收到通知，最好发送的通知和接收通知都在同一个线程中.Objective-C提供了更简单的机制-通知队列(NSNotificationQueue).
NSNotificationQueue定义如下:
@property (class, readonly, strong) NSNotificationQueue *defaultQueue;
#endif
- (instancetype)initWithNotificationCenter:(NSNotificationCenter *)notificationCenter NS_DESIGNATED_INITIALIZER;
- (void)enqueueNotification:(NSNotification *)notification postingStyle:(NSPostingStyle)postingStyle;
- (void)enqueueNotification:(NSNotification *)notification postingStyle:(NSPostingStyle)postingStyle coalesceMask:(NSNotificationCoalescing)coalesceMask forModes:(nullable NSArray *)modes;
- (void)dequeueNotificationsMatching:(NSNotification *)notification coalesceMask:(NSUInteger)coalesceMask;
注册通知:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData6:) name:@"updateData6" object:nil];
异步发送消息:
NSNotification *myNotification = [NSNotification notificationWithName:@"updateData6" object:nil];
[[NSNotificationQueue defaultQueue] enqueueNotification:myNotification postingStyle:NSPostWhenIdle coalesceMask:NSNotificationCoalescingOnName forModes:nil];
NSLog(@"NSNotificationQueue---通知结束");
执行代码:
- (void)updateData6:(NSNotification *)notificaton {
sleep(2);
NSLog(@"NSNotificationQueue收到通知6---%@",notificaton);
}
关于通知队列有两个枚举比较重要:
typedef NS_ENUM(NSUInteger, NSPostingStyle) {
NSPostWhenIdle = 1,
NSPostASAP = 2,
NSPostNow = 3
};
typedef NS_OPTIONS(NSUInteger, NSNotificationCoalescing) {
NSNotificationNoCoalescing = 0,
NSNotificationCoalescingOnName = 1,
NSNotificationCoalescingOnSender = 2
};
NSPostingStyle设置消息发送的时机:
NSPostWhenIdle:在runloop空闲时发送，当runloop要退出时，不会发送.
NSPostASAP:Posting As Soon As Possible，在runloop的当前迭代完成时发送给通知中心，但是当前mode和设定的mode要一致.
NSPostNow:同步调用.
NSNotificationCoalescing是指消息聚合，默认不聚合.
NSNotificationCoalescingOnName：根据通知名称来聚合，如果一段时间多个消息通知，只执行一次.
NSNotificationCoalescingOnSender：根据发送方来聚合.
以下代码聚合类型设置为NSNotificationNoCoalescing执行五次，如果设置为聚合类型，通知只执行一次.
for (NSInteger i = 0; i < 5; i++) {
NSNotification *myNotification = [NSNotification notificationWithName:@"updateData6" object:nil];
[[NSNotificationQueue defaultQueue] enqueueNotification:myNotification postingStyle:NSPostWhenIdle coalesceMask:NSNotificationCoalescingOnName forModes:nil];
}
NSLog(@"NSNotificationQueue---通知结束");
自定义实现
通知是典型的观察者模式，可以通过NSNotificationCenter提供的方法进行简单的通知实现模拟.
FENotification定义:
@interface FENotification : NSObject
@property (copy, nonatomic) NSString *name;
@property (strong, nonatomic) id object;
@property (copy, nonatomic) NSDictionary *userInfo;
@end
FENotificationCenter定义:
@interface FENotificationCenter : NSObject
@property (class, readonly, strong) FENotificationCenter *defaultCenter;
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(NSString *)aName object:(nullable id)anObject;
- (void)postNotification:(NSString *)notification;
- (void)postNotificationName:(NSString *)aName object:(nullable id)anObject;
- (void)postNotificationName:(NSString *)aName object:(nullable id)anObject userInfo:(nullable NSDictionary *)aUserInfo;
- (void)removeObserver:(id)observer;
- (void)removeObserver:(id)observer name:(nullable NSString *)aName object:(nullable id)anObject;
- (id )addObserverForName:(nullable NSString *)name object:(nullable id)obj queue:(nullable NSOperationQueue *)queue usingBlock:(void (^)(FENotification *note))block NS_AVAILABLE(10_6, 4_0);
// The return value is retained by the system, and should be held onto by the caller in
// order to remove the observer with removeObserver: later, to stop observation.
@end
FENotificationModel定义:
typedef void(^OperationBlock)(FENotification *notification);
@interface FENotificationModel: NSObject
@property (strong, nonatomic) id observer;
@property (assign, nonatomic) SEL sel;
@property (copy, nonatomic) NSString *notificationName;
@property (strong, nonatomic) id object;
@property (strong, nonatomic) NSOperationQueue *operationQueue;
@property (copy, nonatomic) OperationBlock block;
@end
@implementation FENotificationModel
@end
消息通知内部通过通知名称作为key，多个FENotificationModel对象的数组作为value.
@interface FENotificationCenter()
@property (strong, nonatomic) NSMutableDictionary *observerDict;
@end
单例实现:
#pragma mark - LifeCycle
+ (FENotificationCenter *)defaultCenter {
static FENotificationCenter *sharedCenter = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedCenter = [[FENotificationCenter alloc] init];
});
return sharedCenter;
}
#pragma mark - Accessors
- (NSMutableDictionary *)observerDict {
if (!_observerDict) {
_observerDict = [[NSMutableDictionary alloc] init];
}
return _observerDict;
}
添加观察者:
- (void)addObserver:(id)observer selector:(SEL)aSelector name:(NSString *)aName object:(id)anObject {
FENotificationModel *model = [[FENotificationModel alloc] init];
model.observer = observer;
model.sel = aSelector;
model.notificationName = aName;
model.object = anObject;
NSMutableArray *value = [self.observerDict objectForKey:aName];
if ([value count]) {
[value addObject:model];
} else {
NSMutableArray *arr = [[NSMutableArray alloc] init];
[arr addObject:model];
self.observerDict[aName] = arr;
}
}
- (id)addObserverForName:(NSString *)name object:(id)obj queue:(NSOperationQueue *)queue usingBlock:(void (^)(FENotification *))block {
FENotificationModel *model = [[FENotificationModel alloc] init];
model.notificationName = name;
model.operationQueue = queue;
model.block = block;
NSMutableArray *value = [self.observerDict objectForKey:name];
if ([value count]) {
[value addObject:model];
} else {
NSMutableArray *arr = [[NSMutableArray alloc] init];
[arr addObject:model];
self.observerDict[name] = arr;
}
return nil;
}
发送通知实现:
- (void)postNotification:(NSString *)notification {
[self postNotificationName:notification object:nil];
}
- (void)postNotificationName:(NSString *)aName object:(id)anObject {
[self postNotificationName:aName object:anObject userInfo:nil];
}
- (void)postNotificationName:(NSString *)aName object:(id)anObject userInfo:(NSDictionary *)aUserInfo {
NSMutableArray *value = self.observerDict[aName];
if ([value count]) {
for (FENotificationModel *model in value) {
if (model.operationQueue) {
NSOperationQueue *queue = model.operationQueue;
NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
FENotification *notification = [FENotification new];
notification.name = model.notificationName;
model.block(notification);
}];
[queue addOperation:blockOperation];
} else {
id observer = model.observer;
SEL sel = model.sel;
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
FENotification *notification = [FENotification new];
notification.name = aName;
notification.object = anObject;
notification.userInfo = aUserInfo;
[observer performSelector:sel withObject:notification];
}
}
}
}
移除观察者:
- (void)removeObserver:(id)observer {
for (NSString *key in [self.observerDict allKeys]) {
NSMutableArray *data = self.observerDict[key];
NSMutableArray *newData = [NSMutableArray new];
for (NSInteger i=0; i < [data count]; i++) {
FENotificationModel *model = data[i];
if (model.observer != observer) {
[newData addObject:model];
}
}
if ([newData count] == 0) {
[self.observerDict removeObjectForKey:key];
} else {
self.observerDict[key] = newData;
}
}
}
- (void)removeObserver:(id)observer name:(NSString *)aName object:(id)anObject {
for (NSString *key in [self.observerDict allKeys]) {
if (key == aName) {
NSMutableArray *data = self.observerDict[key];
NSMutableArray *newData = [NSMutableArray new];
for (NSInteger i=0; i < [data count]; i++) {
FENotificationModel *model = data[i];
if (model.observer != observer) {
[newData addObject:model];
}
}
if ([newData count] == 0) {
[self.observerDict removeObjectForKey:key];
} else {
self.observerDict[key] = newData;
}
}
}
}
参考链接:
NSNotifications