Objective-C的通知是負責(zé)對象之間的通信，可以在NSNotificationCenter中注冊觀察對象，對象也可以NSNotificationCenter發(fā)送消息通知.發(fā)送對象和接收對象是一對多的關(guān)系，通知算是多播(multiCast)形式的一種，如果是向非特定的多個對象發(fā)送消息稱之為廣播(broadcast).
同步 or 異步
通知的注冊和發(fā)送都是在NSNotificationCenter中實現(xiàn)的，注冊觀察者，發(fā)送消息，還有非常重要的對象銷毀的時候注意移除通知.
- (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 <NSObject>)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.
注冊觀察者:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData1:) name:@"updateData" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData2:) name:@"updateData" object:nil];
發(fā)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);
}
執(zhí)行結(jié)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] 通知執(zhí)行完成
調(diào)用通知的方法時，所有相關(guān)的觀察者都會被有序的發(fā)送通知消息，是一個同步的過程，我們可以在收到消息之后異步執(zhí)行代碼，通知如果是在子線程中發(fā)出，主線程也會收到通知，最好發(fā)送的通知和接收通知都在同一個線程中.Objective-C提供了更簡單的機制-通知隊列(NSNotificationQueue).
NSNotificationQueue定義如下:
@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<NSRunLoopMode> *)modes;
- (void)dequeueNotificationsMatching:(NSNotification *)notification coalesceMask:(NSUInteger)coalesceMask;
注冊通知:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateData6:) name:@"updateData6" object:nil];
異步發(fā)送消息:
NSNotification *myNotification = [NSNotification notificationWithName:@"updateData6" object:nil];
[[NSNotificationQueue defaultQueue] enqueueNotification:myNotification postingStyle:NSPostWhenIdle coalesceMask:NSNotificationCoalescingOnName forModes:nil];
NSLog(@"NSNotificationQueue---通知結(jié)束");
執(zhí)行代碼:
- (void)updateData6:(NSNotification *)notificaton {
sleep(2);
NSLog(@"NSNotificationQueue收到通知6---%@",notificaton);
}
關(guān)于通知隊列有兩個枚舉比較重要:
typedef NS_ENUM(NSUInteger, NSPostingStyle) {
NSPostWhenIdle = 1,
NSPostASAP = 2,
NSPostNow = 3
};
typedef NS_OPTIONS(NSUInteger, NSNotificationCoalescing) {
NSNotificationNoCoalescing = 0,
NSNotificationCoalescingOnName = 1,
NSNotificationCoalescingOnSender = 2
};
NSPostingStyle設(shè)置消息發(fā)送的時機:
NSPostWhenIdle:在runloop空閑時發(fā)送，當(dāng)runloop要退出時，不會發(fā)送.
NSPostASAP:Posting As Soon As Possible，在runloop的當(dāng)前迭代完成時發(fā)送給通知中心，但是當(dāng)前mode和設(shè)定的mode要一致.
NSPostNow:同步調(diào)用.
NSNotificationCoalescing是指消息聚合，默認不聚合.
NSNotificationCoalescingOnName：根據(jù)通知名稱來聚合，如果一段時間多個消息通知，只執(zhí)行一次.
NSNotificationCoalescingOnSender：根據(jù)發(fā)送方來聚合.
以下代碼聚合類型設(shè)置為NSNotificationNoCoalescing執(zhí)行五次，如果設(shè)置為聚合類型，通知只執(zhí)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---通知結(jié)束");
自定義實現(xiàn)
通知是典型的觀察者模式，可以通過NSNotificationCenter提供的方法進行簡單的通知實現(xiàn)模擬.
FENotification定義:
@interface FENotification : NSObject
@property (copy, nonatomic) NSString *name;
@property (strong, nonatomic) id object;
@property (copy, nonatomic) NSDictionary *userInfo;
@end
FENotificationCenter定義:
@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 <NSObject>)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定義:
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
消息通知內(nèi)部通過通知名稱作為key，多個FENotificationModel對象的數(shù)組作為value.
@interface FENotificationCenter()
@property (strong, nonatomic) NSMutableDictionary *observerDict;
@end
單例實現(xiàn):
#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;
}
添加觀察者:
- (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<NSObject>)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;
}
發(fā)送通知實現(xiàn):
- (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];
}
}
}
}
移除觀察者:
- (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;
}
}
}
}
參考鏈接:
NSNotifications
