Subject介绍
- Subject 既是 Observer 也是 Observable 。它可以订阅一个或多个 Observable,当收到消息后进行处理,也可以通过Event将数据发送给订阅者。
- 一共有四种Subject,PublishSubject、BehaviorSubject、ReplaySubject、BehaviorRelay、Variable(废弃、用BehaviorRelay替代),他们最大区别在于:当一个新的订阅者订阅它的时候,能否收到Subject以前发出过的就的Event,如果可以的会,又能收到多少个
- PublishSubject
当订阅者订阅PublishSubject 时,只会收到订阅后Subject发出的新Event,而不会收到订阅之前发出的旧Event
func publishSubject() {
let subject = PublishSubject<String>()
subject.onNext("A") //不会收到
subject.subscribe(onNext: { element in
print("第1次订阅:", element)
}, onCompleted: {
print("第1次订阅:completed")
}).disposed(by: bag)
subject.onNext("B") //1订阅收到
subject.subscribe(onNext: { element in
print("第2次订阅:", element)
}, onCompleted: {
print("第2次订阅:completed")
}).disposed(by: bag)
subject.onNext("C") //1、2订阅会收到