Subjects 介绍
1. Subjects 是订阅者，也是Observable
订阅者：它能动态的接收新的值。
Observable： 当Subjects有了新值后会通过Event将新值发出给他的所有订阅者。
2. 常用的方法
3. Subjects 有四种PublishSubject、BehaviorSubject、ReplaySubject、Variable
相同点
不同点
let sub = PublishSubject<String>()
sub.onNext("订阅之前的不能接收到")
sub.subscribe { event in
print(event.element)
//Optional("订阅之后的可以接收到")
//nil
}.disposed(by: disposeBag)
sub.onNext("订阅之后的可以接收到")
//结束
sub.onCompleted()
/// 结束之后添加的订阅能收到 completed
sub.subscribe { event in
print(event)
}
sub.onNext("结束后发的都收不到")
BehaviorSubject
需要一个默认值初始化
当一个订阅者订阅之后会立马收到上一个Event，之后就是正常情况发一个收一个。
onCompleted()之后的订阅者也只能收到Completed。
let sub = BehaviorSubject(value: "默认值")
sub.subscribe { event in
print("订阅1", event)
}.disposed(by: disposeBag)
sub.onNext("发送1")
sub.subscribe { event in
print("订阅2", event)
}.disposed(by: disposeBag)
sub.onCompleted()
sub.subscribe { event in
print("订阅3", event)
}.disposed(by: disposeBag)
订阅1 next(默认值)
订阅1 next(发送1)
订阅2 next(发送1)
订阅1 completed
订阅2 completed
订阅3 completed
ReplaySubject
创建的时候需要一个参数bufferSize设置记录个数
新添加的订阅会接收到之前发送的两个 Event，如果不足两个就只接收一个。
如果超过两个只接收最新的两个。
如果订阅时已经结束除了会接收到最新的两个Event外还有结束的complete或error。
let sub = ReplaySubject<String>.create(bufferSize: 2)
sub.subscribe { event in
print("订阅1", event)
}.disposed(by: disposeBag)
sub.onNext("发送1")
print("-------")
sub.subscribe { event in
print("订阅2", event)
}.disposed(by: disposeBag)
sub.onNext("发送2")
sub.onNext("发送3")
sub.onNext("发送4")
print("-------")
sub.subscribe { event in
print("订阅3", event)
}.disposed(by: disposeBag)
sub.onCompleted()
print("-------")
/// 不仅会收到最后的两个 event 还有 Completed
sub.subscribe { event in
print("订阅4", event)
}
订阅1 next(发送1)
-------
订阅2 next(发送1)
订阅1 next(发送2)
订阅2 next(发送2)
订阅1 next(发送3)
订阅2 next(发送3)
订阅1 next(发送4)
订阅2 next(发送4)
-------
订阅3 next(发送3)
订阅3 next(发送4)
订阅1 completed
订阅2 completed
订阅3 completed
-------
订阅4 next(发送3)
订阅4 next(发送4)
订阅4 completed
BehaviorRelay
基本同 BehaviorSubject功能一样，但是不能主动调用onCompleted和error，会在BehaviorRelay释放前调用
let sub = BehaviorRelay(value: "初始值")
sub.subscribe { event in
print("第一次订阅", event)
}.disposed(by: disposeBag)
sub.accept("新值1")
sub.subscribe { event in
print("第二次订阅", event)
}.disposed(by: disposeBag)
