给通知和KVO添加block实现

给通知添加block的实现

1. 创建NSObject分类并创建分类方法(带通知名参数和block回调参数)

  if (!name || !block) return;
    dispatch_semaphore_t notificationSemaphore = [self _xw_getSemaphoreWithKey:XWNotificationSemaphoreKey];
    dispatch_semaphore_wait(notificationSemaphore, DISPATCH_TIME_FOREVER);
    NSMutableDictionary *allTargets = objc_getAssociatedObject(self, XWNotificationBlockKey);
    if (!allTargets) {
        allTargets = @{}.mutableCopy;
        objc_setAssociatedObject(self, XWNotificationBlockKey, allTargets, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    _XWBlockTarget *target = allTargets[name];
    if (!target) {
        target = [_XWBlockTarget new];
        allTargets[name] = target;
        [[NSNotificationCenter defaultCenter] addObserver:target selector:@selector(xw_doNotification:) name:name object:nil];
    }
    [target xw_addNotificationBlock:block];
    [self _xw_swizzleDealloc];
    dispatch_semaphore_signal(notificationSemaphore);

如果通知名为空或者block为空直接返回，调用懒加载方法_xw_getSemaphoreWithKey获取信号量对象，信号量等待，懒加载获取关联属性targets字典，从targets字典中取出对应通知名的target对象(如果没有就创建一个，并保存到字典中，将给系统的通知中心注册observer为target的通知，执行方法为target中的方法，target的方法中调用block)，通知中心添加对应的通知名的通知，target的blockset添加对应的block
当调用分类的发送通知的方法的时候，利用系统的通知中心发送通知，target对象的就能收到通知，target对象调用block，分类中注册通知方法中的block被调用，完成回调

给KVO添加block回调的实现

调用分类的addObserver方法，懒加载创建信号量，信号量等待，通过关联属性方法获取block字典，如果没有分类关联属性，则创建并设置关联属性，通过可以path从关联属性字典中获取到target，如果target为空则创建target对象，并将target对象保存到字典，将target对象设置为本方法调用者的监听也就是调用addObserver方法。路径为keypath，如果target对象存在则直接给target对象的block数组中添加block。发送信号，取消信号量限制。

- (void)xw_addObserverBlockForKeyPath:(NSString*)keyPath block:(void (^)(id obj, id oldVal, id newVal))block {
   if (!keyPath || !block) return;
   dispatch_semaphore_t kvoSemaphore = [self _xw_getSemaphoreWithKey:XWKVOSemaphoreKey];
   dispatch_semaphore_wait(kvoSemaphore, DISPATCH_TIME_FOREVER);
   //取出存有所有KVOTarget的字典
   NSMutableDictionary *allTargets = objc_getAssociatedObject(self, XWKVOBlockKey);
   if (!allTargets) {
       //没有则创建
       allTargets = [NSMutableDictionary new];
       //绑定在该对象中
       objc_setAssociatedObject(self, XWKVOBlockKey, allTargets, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
   }
   //获取对应keyPath中的所有target
   _XWBlockTarget *targetForKeyPath = allTargets[keyPath];
   if (!targetForKeyPath) {
       //没有则创建
       targetForKeyPath = [_XWBlockTarget new];
       //保存
       allTargets[keyPath] = targetForKeyPath;
       //如果第一次，则注册对keyPath的KVO监听
       [self addObserver:targetForKeyPath forKeyPath:keyPath options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:NULL];
   }
   [targetForKeyPath xw_addBlock:block];
   //对第一次注册KVO的类进行dealloc方法调剂
   [self _xw_swizzleDealloc];
   dispatch_semaphore_signal(kvoSemaphore);
}

target对象实现observer代理方法，当观察的keypath发生变化的时候，target枚举自己block数组中的block并一一调用。

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
   if (!_kvoBlockSet.count) return;
   BOOL prior = [[change objectForKey:NSKeyValueChangeNotificationIsPriorKey] boolValue];
   //只接受值改变时的消息
   if (prior) return;
   NSKeyValueChange changeKind = [[change objectForKey:NSKeyValueChangeKindKey] integerValue];
   if (changeKind != NSKeyValueChangeSetting) return;
   id oldVal = [change objectForKey:NSKeyValueChangeOldKey];
   if (oldVal == [NSNull null]) oldVal = nil;
   id newVal = [change objectForKey:NSKeyValueChangeNewKey];
   if (newVal == [NSNull null]) newVal = nil;
   //执行该target下的所有block
   [_kvoBlockSet enumerateObjectsUsingBlock:^(void (^block)(__weak id obj, id oldVal, id newVal), BOOL * _Nonnull stop) {
       block(object, oldVal, newVal);
   }];
}

移除通知和观察者

- (void)xw_removeNotificationForName:(NSString *)name{
   if (!name) return;
   NSMutableDictionary *allTargets = objc_getAssociatedObject(self, XWNotificationBlockKey);
   if (!allTargets.count) return;
   _XWBlockTarget *target = allTargets[name];
   if (!target) return;
   dispatch_semaphore_t notificationSemaphore = [self _xw_getSemaphoreWithKey:XWNotificationSemaphoreKey];
   dispatch_semaphore_wait(notificationSemaphore, DISPATCH_TIME_FOREVER);
   [[NSNotificationCenter defaultCenter] removeObserver:target];
   [allTargets removeObjectForKey:name];
   dispatch_semaphore_signal(notificationSemaphore);
   
}

- (void)xw_removeAllNotification{
   NSMutableDictionary *allTargets = objc_getAssociatedObject(self, XWNotificationBlockKey);
   if (!allTargets.count) return;
   dispatch_semaphore_t notificationSemaphore = [self _xw_getSemaphoreWithKey:XWNotificationSemaphoreKey];
   dispatch_semaphore_wait(notificationSemaphore, DISPATCH_TIME_FOREVER);
   [allTargets enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, _XWBlockTarget *target, BOOL * _Nonnull stop) {
       [[NSNotificationCenter defaultCenter] removeObserver:target];
   }];
   [allTargets removeAllObjects];
   dispatch_semaphore_signal(notificationSemaphore);
}