何时使用 doOnTerminate 与 doOnUnsubscribe? [英] When to use doOnTerminate vs doOnUnsubscribe?

问题描述

当有东西订阅了我的 observable 时，我需要得到通知.我还需要被通知 observable 已出错或已完成.所以我想我应该使用 doOnSubscribe:

I need to be notified when something subscribes to my observable. I also need to be notified that the observable has either errored or completed. So I thought I should use doOnSubscribe:

注册当观察者订阅时采取的行动可观察

register an action to take when an observer subscribes to an Observable

和doOnTerminate:

注册一个 Observable 完成时要执行的操作，或者成功或有错误

register an action to take when an Observable completes, either successfully or with an error

然后我看到了doOnUnsubscribe:

注册当观察者取消订阅时要采取的行动可观察

register an action to take when an observer unsubscribes from an Observable

并认为 doOnSubscribe/doOnUnsubscribe 的对称性会更好.

and thought the symmetry of doOnSubscribe/doOnUnsubscribe would be better.

那么，doOnTerminate 是否总是在 doOnUnsubscribe 之前被调用?如果我只想知道事情已经完成"，那么我选择哪个真的重要吗?

So, will doOnTerminate always be called before doOnUnsubscribe? If I just want to know that things are "done", does it really matter which I choose?

推荐答案

在响应式流程中取消订阅的方式将决定您可以使用 doOnUnsubscribe 或 doOnTerminate 中的哪一个.可能是以下情况:

The way unsubscribe happens in your reactive flow will determine which one from doOnUnsubscribe or doOnTerminate you can use. The following can be the cases:

可观察到的完成/错误触发取消订阅
在这种情况下，doOnTerminate 和 doOnUnsubscribe 都将被调用，doOnTerminate 将首先被调用.

Observable completion/error triggers unsubscribe
In such a scenario both doOnTerminate and doOnUnsubscribe will be called with doOnTerminate being called first.

下面的示例将打印 termination 和 unsubscribed.

The below example will print both terminated and unsubscribed.

Subscription subscribe = Observable.empty() // source terminates immediately
    .subscribeOn(Schedulers.newThread()) 
    .doOnTerminate(() -> System.out.println("terminated"))
    .doOnUnsubscribe(() -> System.out.println("unsubscribed"))
    .subscribe();

TimeUnit.SECONDS.sleep(1);
subscribe.unsubscribe(); // by this time already unsubscribe would have happened

在 Observable 完成之前取消订阅的程序调用
在这种情况下，只会调用 doOnUnsubscribe.当您有一个无限运行的源或一个像用户点击的 observable 一样热的源时，发生这种情况的可能性更大.

Programatic call to unsubscribe before Observable completes
In such a scenario only doOnUnsubscribe will be called. The chance of this happening is more prevalent when you have a source which runs infinitely or a source which is hot like an observable for user clicks.

下面的例子只会打印unsubscribed.

Subscription subscribe = Observable.never() // source never terminates
    .subscribeOn(Schedulers.newThread())
    .doOnTerminate(() -> System.out.println("terminated"))
    .doOnUnsubscribe(() -> System.out.println("unsubscribed"))
    .subscribe();

TimeUnit.SECONDS.sleep(1);
subscribe.unsubscribe(); // this will trigger unsubscribe

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