📅 最后修改于: 2020-11-12 05:30:25 🧑 作者: Mango
根据反应式，主体可以同时充当可观察者和观察者。
主题是一种在ReactiveX的某些实现中可用的桥梁或代理，它既充当观察者又充当Observable。因为它是观察者，所以可以订阅一个或多个Observable，并且因为它是Observable，所以可以通过释放观察到的项来传递它们，也可以发出新的项。
有四种类型的主题-
| Sr.No. | Subject & Description |
|---|---|
| 1 |
Publish Subject Emits only those items which are emitted after time of subscription. |
| 2 |
Replay Subject
Emits all the items emitted by source Observable regardless of when it has subscribed the Observable. |
| 3 |
Behavior Subject Upon subscription, emits the most recent item then continue to emit item emitted by the source Observable. |
| 4 |
Async Subject Emits the last item emitted by the source Observable after it’s completes emission. |