# PublishSubject

![](https://4217506537-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MWj545abP2yK86-qksJ%2Fsync%2F9bcf53b8b48e627a64a57adceb9d73bdfb4fd23c.png?generation=1616819378880757\&alt=media)

**PublishSubject** 将对观察者发送订阅后产生的元素，而在订阅前发出的元素将不会发送给观察者。如果你希望观察者接收到所有的元素，你可以通过使用 `Observable` 的 `create` 方法来创建 `Observable`，或者使用 [ReplaySubject](https://3440217568.gitbook.io/rxswift/rxswift_core/observable_and_observer/replay_subject)。

![](https://4217506537-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-MWj545abP2yK86-qksJ%2Fsync%2Faa9a5cce45580fad9396f7dfa876a850ef625c01.png?generation=1616819378727274\&alt=media)

如果源 `Observable` 因为产生了一个 `error` 事件而中止， **PublishSubject** 就不会发出任何元素，而是将这个 `error` 事件发送出来。

## 演示

```swift
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("🅰️")
subject.onNext("🅱️")
```

**输出结果：**

```swift
Subscription: 1 Event: next(🐶)
Subscription: 1 Event: next(🐱)
Subscription: 1 Event: next(🅰️)
Subscription: 2 Event: next(🅰️)
Subscription: 1 Event: next(🅱️)
Subscription: 2 Event: next(🅱️)
```