iOS通过NSNotificationCenter来传递通告(Notification)的原理非常简单。
俗一点的原理如下：这个电线杆就是一个NotificationCenter. 谁都可以来发通告(Notification)，谁都可以来看通告(Notification)。
NotificationCenter
雅一点的原理如下:
学术一点
先讲讲俗的原理
电线杆上的牛皮癣广告包含了至少三个参与方:
- 电线杆 (充当NSNotificationCenter的角色)
- 有祖传老中医的广告张贴者 (充当Poster的角色)
- 有祖传牛皮癣的路人甲乙丙丁 (充当Observer的角色)
发送notification(贴小广告的来了)
方法一不用传递更多的信息，函数如下:
[NSNotificationCenter defaultCenter] postNotificationName:@"notificationName" object:nil];
方法二可以传递更多的信息，使用userInfo这个参数，函数如下:
// UserDataObject.h
@property (nonatomic, strong) NSString *property;
// Publisher.m
UserDataObject *userDataObject = [DataObject new];
userDataObject.property = @"This is property value";
NSDictionary *userInfo = [NSDictionary dictionaryWithObject:userDataObject
forKey:@"additionalData"];
[[NSNotificationCenter defaultCenter] postNotificationName:@"MyNotification"
object:nil
userInfo:userInfo];
注册Notification, 添加observer (看小广告的来了)
上一步有notification发送出来，必须要有相应的observer来响应这些notification, 并对这些notification采取响应的措施。
方法一
// 添加observer
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(eventListenerDidReceiveNotification:)
name:@"MyNotification"
object:nil];
// 对notification采取的动作
- (void)eventListenerDidReceiveNotification:(NSNotification *)notification
{
if ([[notification name] isEqualToString:@"MyNotification"])
{
NSLog(@"Successfully received the notification!");
NSDictionary *userInfo = notification.userInfo;
UserDataObject *userDataObject = [userInfo objectForKey:@"additionalData"];
// Your response to the notification should be placed here
NSLog(@"userDataObject.property -> %@", userDataObject.property1);
}
}
方法二(采用了block)
self.observer = [[NSNotificationCenter defaultCenter] addObserverForName:@"MyNotification" object:nil queue:nil usingBlock:^(NSNotification *notif) {
if ([[notif name] isEqualToString:@"MyNotification"])
{
NSLog(@"Successfully received the notification!");
NSDictionary *userInfo = notif.userInfo;
DataObject *dataObject = [userInfo objectForKey:@"additionalData"];
// Your response to the notification should be placed here
NSLog(@"dataObject.property1 -> %@", dataObject.property1);
}
}];
移除
当observer收到信息并完成操作后，不想再接收信息。
// If registered using addObserver:... method
[[NSNotificationCenter defaultCenter] removeObserver:self];
// If registered using addObserverForName:... method
[[NSNotificationCenter defaultCenter] removeObserver:self.observer];
self.observer = nil;
// You can also unregister notification types/names using
[[NSNotificationCenter defaultCenter] removeObserver:self name:@"MyNotification" object:nil];
参考文献:
iOS - 使用通知中心(NotificationCenter)進行傳值
Notifications in iOS Part 1 – Broadcasting Events via NSNotificationCenter
