RxSwift 3.Subject(Observable & Observer)

文章目录

1. AsyncSubject
2. PublishSubject
3. ReplaySubject
4. BehaviorSubject
5. Variable（弃用）
6. Relay
1. 6.1. PublishRelay
2. 6.2. BehaviorRelay

首先在开发的时候思考，他是一个 Observable

AsyncSubject

特点：
- 当 Observable Sequence 发送 complete 事件，AsyncSubject 才会发送最后一个 next 事件和 complete
- 当 Observable Sequence 发送 error 事件，AsyncSubject 只发送 error 事件，不会发送最后一个 next

2. 演示

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let disposeBag = DisposeBag() 
let subject = AsyncSubject<String>()
subject
    .subscribe { print("Subscription: 1 Event:", $0) } 
    .disposed(by: disposeBag)
subject.onNext("  ")
subject.onNext("  ")
subject.onNext("  ")
subject.onCompleted()
输出结果：
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Subscription: 1 Event: next(ί )
Subscription: 1 Event: completed

PublishSubject

特点：
- PublishSubject 发送订阅后产⽣的元素.
- PublishSubject 不发送订阅前产⽣的元素.

2. 演示

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let disposeBag = DisposeBag()
let subject = PublishSubject<String>()
subject
    .subscribe { print("Subscription: 1 Event:", $0) }
    .disposed(by: disposeBag)
subject.onNext("  ")
subject.onNext("  ")
subject
    .subscribe { print("Subscription: 2 Event:", $0) }
    .disposed(by: disposeBag)
subject.onNext("A ")
subject.onNext("B ")
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Subscription: 1 Event: next(  )
Subscription: 1 Event: next(  )
Subscription: 1 Event: next(A )
Subscription: 2 Event: next(A )
Subscription: 1 Event: next(B )
Subscription: 2 Event: next(B )

ReplaySubject

特点：
- ReplaySubject 将对观察者发送全部的元素，⽆论观察者是何时进⾏订阅的。

2. 演示

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let disposeBag = DisposeBag()
let subject = ReplaySubject<String>.create(bufferSize: 1)
subject
    .subscribe { print("Subscription: 1 Event:", $0) }
    .disposed(by: disposeBag)
subject.onNext("  ")
subject.onNext("  ")
subject
    .subscribe { print("Subscription: 2 Event:", $0) }
    .disposed(by: disposeBag)
subject.onNext("A ")
subject.onNext("B ")
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Subscription: 1 Event: next(  ) 
Subscription: 1 Event: next(  ) 
Subscription: 2 Event: next(  )
Subscription: 1 Event: next(A )
Subscription: 2 Event: next(A )
Subscription: 1 Event: next(B )
Subscription: 2 Event: next(B )

BehaviorSubject

特点：
1. 具有默认值
2. 当订阅 BehaviorSubject 时，它会将源 Observable 中最新的元素发送出来（如果不存在最新的元素，就发出默认元素）。然后将随后产⽣的元素发送出来。
3. 如果 Observable 发 error 事件，那么BehaviorSubject不会再发送 next 事件，而只是传递来自源 Observable 的 error 事件。

normal

error

2. 演示

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let disposeBag = DisposeBag()
let subject = BehaviorSubject(value: "  ")
subject
    .subscribe { print("Subscription: 1 Event:", $0) } 
    .disposed(by: disposeBag)

subject.onNext("  ") 
subject.onNext("  ") 
subject 
    .subscribe { print("Subscription: 2 Event:", $0) } 
    .disposed(by: disposeBag)

subject.onNext("A ") 
subject.onNext("B ") 
subject 
    .subscribe { print("Subscription: 3 Event:", $0) } 
    .disposed(by: disposeBag) 
subject.onNext("  ") 
subject.onNext("  ")
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Subscription: 1 Event: next(  )
Subscription: 1 Event: next(  )
Subscription: 1 Event: next(  )
Subscription: 2 Event: next(  )
Subscription: 1 Event: next(A )
Subscription: 2 Event: next(A )
Subscription: 1 Event: next(B )
Subscription: 2 Event: next(B )
Subscription: 3 Event: next(B )
Subscription: 1 Event: next(  )
Subscription: 2 Event: next(  )
Subscription: 3 Event: next(  )
Subscription: 1 Event: next(  )
Subscription: 2 Event: next(  )
Subscription: 3 Event: next(  )

Variable（弃用）

在 RxSwift 5.x 中，他被官⽅的正式的弃⽤了，并且在需要时，推荐使⽤ BehaviorRelay 或者 BehaviorSubject。

Relay

RxRelay提供两种中继：PublishRelay 和 BehaviorRelay。它们的行为与对应的 Subjects 完全相同，但有两个变化：

Relays never complete.
Relays never emit errors.

本质上，中继仅发出.next事件，并且永不终止，有了他，我们将 API 转化为 Rx 样式时，就不必担⼼⼀个意外的终⽌事件，导致后续事件转发失效。

PublishRelay

PublishRelay 就是 PublishSubject 去掉终⽌事件 onError 和 onCompleted。

示例：

let disposeBag = DisposeBag() 
let relay = PublishRelay<String>() 
relay 
    .subscribe { print("Event:", $0) } 
    .disposed(by: disposeBag)
relay.accept("  ")
relay.accept("  ")

// output
Event: next( )
Event: next( )

BehaviorRelay

BehaviorRelay 就是 BehaviorSubject 去掉终⽌事件 onError 和 onCompleted。

示例：

let disposeBag = DisposeBag() 
let relay = BehaviorRelay(value: "  ")
relay 
    .subscribe { print("Event:", $0) } 
    .disposed(by: disposeBag)
relay.accept("  ")
relay.accept("  ")

// output
Event: next( )
Event: next( )
Event: next( )