本文共 2995 字，大约阅读时间需要 9 分钟。

前言

前面写过RxJava类似观察者模式,但是一直没提到RxJava如何取消订阅,今天就来学习一下.

Subscription

RxJava中有个叫做Subscription的接口,可以用来取消订阅.

public interface Subscription {    /**     * Stops the receipt of notifications on the {@link Subscriber} that was registered when this Subscription     * was received.     * 
     * This allows unregistering an {@link Subscriber} before it has finished receiving all events (i.e. before     * onCompleted is called).     */    void unsubscribe();    /**     * Indicates whether this {@code Subscription} is currently unsubscribed.     *     * @return {@code true} if this {@code Subscription} is currently unsubscribed, {@code false} otherwise     */    boolean isUnsubscribed();}

从上面可以看到,我们只需要调用unsubscribe就可以取消订阅,那么如何得到一个Subscription对象呢?

其实很简单:

OK,内容其实不多,那么来练习一下吧.

实战

我先写了以下代码来测试:

Subscription subscription = Observable.just("Hello subscription")        .subscribe(new Action1
   
    () {            @Override            public void call(String s) {                System.out.println(s);            }        });System.out.println(subscription.isUnsubscribed());subscription.unsubscribe();System.out.println(subscription.isUnsubscribed());
   

在我想来输出的日志应该是这样的:

Hello subscriptionfalsetrue

但是,结果出乎我的意料,我运行之后是这样的:

Hello subscriptiontruetrue

诶?不对啊,明明我没有取消订阅啊,怎么就true了呢?

接下去我进源码探索了一下发现:

if (!(subscriber instanceof SafeSubscriber)) {    // assign to `observer` so we return the protected version    subscriber = new SafeSubscriber
   
    (subscriber);}
   

它会把我们传递的subscriber转成SafeSubscriber,接下去跟进发现:

public void onCompleted() {    if (!done) {        done = true;        try {            actual.onCompleted();        } catch (Throwable e) {            // we handle here instead of another method so we don't add stacks to the frame            // which can prevent it from being able to handle StackOverflow            Exceptions.throwIfFatal(e);            // handle errors if the onCompleted implementation fails, not just if the Observable fails            _onError(e);        } finally {            // auto-unsubscribe            unsubscribe();        }    }}

原来它在finally里自动取消了订阅!!

那么让onCompleted晚点执行就行了:

Subscription subscription = Observable.just("Hello subscription")        .subscribeOn(Schedulers.newThread())//起线程        .subscribe(new Action1
   
    () {            @Override            public void call(String s) {                try {                    Thread.sleep(5000);//睡5秒,延迟一下                } catch (InterruptedException e) {                    e.printStackTrace();                }                System.out.println(s);            }        });//默认subscription 调用完System.out.println(subscription.isUnsubscribed());subscription.unsubscribe();System.out.println(subscription.isUnsubscribed());
   

Log:

falsetrue

注意,取消订阅了之后Hello subscription并不会打印,你想,你取消了订阅报纸,报社还会给你发报纸么?

好了关于Subscription暂时就探索到这里了.

安利:

微信公众号

转载地址：https://blog.csdn.net/u014400934/article/details/101489960 如侵犯您的版权，请留言回复原文章的地址，我们会给您删除此文章，给您带来不便请您谅解！