Rxjava2的操作符 三

概述:RX的操作符确实不少,本篇将介绍剩余的操作符。

5. 过滤操作符

5.1 filter()
通过一定逻辑来过滤被观察者发送的事件,如果返回 true 则会发送事件,否则不会发送。

 Observable.just(1, 2, 3)
    .filter(new Predicate < Integer > () {
        @Override
        public boolean test(Integer integer) throws Exception {
            return integer < 2;
        }
})
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});

以上代码只有小于2的事件才会发送,来看看打印结果:

==================onSubscribe 
==================onNext 1
==================onComplete 

5.2 ofType()
可以过滤不符合该类型事件

Observable.just(1, 2, 3, "chan", "zhide")
.ofType(Integer.class)
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});

结果

==================onSubscribe 
==================onNext 1
==================onNext 2
==================onNext 3
==================onComplete 

5.3 skip()
跳过正序某些事件,count 代表跳过事件的数量

Observable.just(1, 2, 3)
.skip(2)
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});

打印结果:

==================onSubscribe 
==================onNext 3
==================onComplete 

skipLast() 作用也是跳过某些事件,不过它是用来跳过正序的后面的事件,这里就不再讲解了。

5.4 distinct()
过滤事件序列中的重复事件。

Observable.just(1, 2, 3, 3, 2, 1)
.distinct()
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});


==================onSubscribe 
==================onNext 1
==================onNext 2
==================onNext 3
==================onComplete 

5.5 distinctUntilChanged()
过滤掉连续重复的事件

Observable.just(1, 2, 3, 3, 2, 1)
.distinctUntilChanged()
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});

结果:

==================onSubscribe 
==================onNext 1
==================onNext 2
==================onNext 3
==================onNext 2
==================onNext 1
==================onComplete 

5.6 take()
控制观察者接收的事件的数量。

Observable.just(1, 2, 3, 4, 5)
.take(3)
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "==================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        i += integer;
        Log.d(TAG, "==================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "==================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "==================onComplete ");
    }
});

 ==================onSubscribe 
==================onNext 1
==================onNext 2
==================onNext 3
==================onComplete 

takeLast() 的作用就是控制观察者只能接受事件序列的后面几件事情,这里就不再讲解了

5.7 debounce()
如果两件事件发送的时间间隔小于设定的时间间隔则前一件事件就不会发送给观察者。

Observable.create(new ObservableOnSubscribe < Integer > () {

    @Override
    public void subscribe(ObservableEmitter < Integer > e) throws Exception {
        e.onNext(1);
        Thread.sleep(900);
        e.onNext(2);
    }
})
.debounce(1, TimeUnit.SECONDS)
.subscribe(new Observer < Integer > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "===================onSubscribe ");
    }

    @Override
    public void onNext(Integer integer) {
        Log.d(TAG, "===================onNext " + integer);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "===================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "===================onComplete ");
    }
});

打印结果:

05-25 20:39:10.512 17441-17441/com.example.rxjavademo D/chan: ===================onSubscribe 
05-25 20:39:12.413 17441-17478/com.example.rxjavademo D/chan: ===================onNext 2

可以看到事件1并没有发送出去,现在将间隔时间改为1000,看看打印结果:

 ===================onSubscribe 
 ===================onNext 1
 ===================onNext 2

throttleWithTimeout() 与此方法的作用一样,这里就不再赘述了。

5.8 firstElement() && lastElement()
firstElement() 取事件序列的第一个元素,lastElement() 取事件序列的最后一个元素。

Observable.just(1, 2, 3, 4)
.firstElement()
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "====================firstElement " + integer);
    }
});

Observable.just(1, 2, 3, 4)
.lastElement()
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "====================lastElement " + integer);
    }
});

打印结果:

 ====================firstElement 1
====================lastElement 4

5.9 elementAt() & elementAtOrError()
elementAt() 可以指定取出事件序列中事件,但是输入的 index 超出事件序列的总数的话就不会出现任何结果。这种情况下,你想发出异常信息的话就用 elementAtOrError() 。

Observable.just(1, 2, 3, 4)
.elementAt(0)
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "====================accept " + integer);
    }
});


结果:
====================accept 1

将 elementAt() 的值改为5,这时是没有打印结果的,因为没有满足条件的元素。

替换 elementAt() 为 elementAtOrError(),代码如下:

Observable.just(1, 2, 3, 4)
.elementAtOrError(5)
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "====================accept " + integer);
    }
});

打印结果:

io.reactivex.exceptions.OnErrorNotImplementedException
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java: 704)
at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java: 701)
at io.reactivex.internal.observers.ConsumerSingleObserver.onError(ConsumerSingleObserver.java: 47)
at io.reactivex.internal.operators.observable.ObservableElementAtSingle$ElementAtObserver.onComplete(ObservableElementAtSingle.java: 117)
at io.reactivex.internal.operators.observable.ObservableFromArray$FromArrayDisposable.run(ObservableFromArray.java: 110)
at io.reactivex.internal.operators.observable.ObservableFromArray.subscribeActual(ObservableFromArray.java: 36)
at io.reactivex.Observable.subscribe(Observable.java: 10903)
at io.reactivex.internal.operators.observable.ObservableElementAtSingle.subscribeActual(ObservableElementAtSingle.java: 37)
at io.reactivex.Single.subscribe(Single.java: 2707)
at io.reactivex.Single.subscribe(Single.java: 2693)
at io.reactivex.Single.subscribe(Single.java: 2664)
at com.example.rxjavademo.MainActivity.onCreate(MainActivity.java: 103)
at android.app.Activity.performCreate(Activity.java: 6942)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java: 1126)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java: 2880)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java: 2988)
at android.app.ActivityThread. - wrap14(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java: 1631)
at android.os.Handler.dispatchMessage(Handler.java: 102)
at android.os.Looper.loop(Looper.java: 154)
at android.app.ActivityThread.main(ActivityThread.java: 6682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 1520)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 1410)
Caused by: java.util.NoSuchElementException
at io.reactivex.internal.operators.observable.ObservableElementAtSingle$ElementAtObserver.onComplete(ObservableElementAtSingle.java: 117) 
at io.reactivex.internal.operators.observable.ObservableFromArray$FromArrayDisposable.run(ObservableFromArray.java: 110) 
at io.reactivex.internal.operators.observable.ObservableFromArray.subscribeActual(ObservableFromArray.java: 36) 
at io.reactivex.Observable.subscribe(Observable.java: 10903) 
at io.reactivex.internal.operators.observable.ObservableElementAtSingle.subscribeActual(ObservableElementAtSingle.java: 37) 
at io.reactivex.Single.subscribe(Single.java: 2707) 
at io.reactivex.Single.subscribe(Single.java: 2693) 
at io.reactivex.Single.subscribe(Single.java: 2664) 
at com.example.rxjavademo.MainActivity.onCreate(MainActivity.java: 103) 
at android.app.Activity.performCreate(Activity.java: 6942) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java: 1126) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java: 2880) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java: 2988) 
at android.app.ActivityThread. - wrap14(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java: 1631) 
at android.os.Handler.dispatchMessage(Handler.java: 102) 
at android.os.Looper.loop(Looper.java: 154) 
at android.app.ActivityThread.main(ActivityThread.java: 6682) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 1520) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 1410) 

这时候会抛出 NoSuchElementException 异常。

6. 条件操作符

6.1 all()
判断事件序列是否全部满足某个事件,如果都满足则返回 true,反之则返回 false。

Observable.just(1, 2, 3, 4)
.all(new Predicate < Integer > () {
    @Override
    public boolean test(Integer integer) throws Exception {
        return integer < 5;
    }
})
.subscribe(new Consumer < Boolean > () {
    @Override
    public void accept(Boolean aBoolean) throws Exception {
        Log.d(TAG, "==================aBoolean " + aBoolean);
    }
});


05-26 09:39:51.644 1482-1482/com.example.rxjavademo D/chan: ==================aBoolean true

6.2 takeWhile()
可以设置条件,当某个数据满足条件时就会发送该数据,反之则不发送。

Observable.just(1, 2, 3, 4)
.takeWhile(new Predicate < Integer > () {
    @Override
    public boolean test(Integer integer) throws Exception {
        return integer < 3;
    }
})
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "========================integer " + integer);
    }
});


========================integer 1
========================integer 2

6.3 skipWhile()
可以设置条件,当某个数据满足条件时不发送该数据,反之则发送。

Observable.just(1, 2, 3, 4)
.skipWhile(new Predicate < Integer > () {
    @Override
    public boolean test(Integer integer) throws Exception {
        return integer < 3;
    }
})
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "========================integer " + integer);
    }
});


 ========================integer 3
========================integer 4

6.4 takeUntil()
可以设置条件,当事件满足此条件时,下一次的事件就不会被发送了。

Observable.just(1, 2, 3, 4, 5, 6)
.takeUntil(new Predicate < Integer > () {
    @Override
    public boolean test(Integer integer) throws Exception {
        return integer > 3;
    }
})
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "========================integer " + integer);
    }
});


05-26 09:55:12.918 7933-7933/com.example.rxjavademo D/chan: ========================integer 1
========================integer 2
05-26 09:55:12.919 7933-7933/com.example.rxjavademo D/chan: ========================integer 3
========================integer 4

4满足大于3,所以接下来的5就不再发送了。

6.5 skipUntil()
当 skipUntil() 中的 Observable 发送事件了,原来的 Observable 才会发送事件给观察者。

Observable.intervalRange(1, 5, 0, 1, TimeUnit.SECONDS)
.skipUntil(Observable.intervalRange(6, 5, 3, 1, TimeUnit.SECONDS))
.subscribe(new Observer < Long > () {
    @Override
    public void onSubscribe(Disposable d) {
        Log.d(TAG, "========================onSubscribe ");
    }

    @Override
    public void onNext(Long along) {
        Log.d(TAG, "========================onNext " + along);
    }

    @Override
    public void onError(Throwable e) {
        Log.d(TAG, "========================onError ");
    }

    @Override
    public void onComplete() {
        Log.d(TAG, "========================onComplete ");
    }
});


打印结果
05-26 10:08:50.574 13023-13023/com.example.rxjavademo D/chan: ========================onSubscribe 
05-26 10:08:53.576 13023-13054/com.example.rxjavademo D/chan: ========================onNext 4
05-26 10:08:54.576 13023-13054/com.example.rxjavademo D/chan: ========================onNext 5
========================onComplete 

第一个Observable的意思是延迟0秒,然后每隔一秒钟,从一开始发,发送到5。也就是第一秒发送2,第二秒发送3,第三秒发送4,第四秒发送5。然后结束。
第一个Observable的意思是延迟3秒开始发送。
综合来看就是,一直到三秒过后,第二个Observable开始发送数据,第一个才开始发送,此时发送的是4和5。而第二个Observable其实压根就没去接收它发送的数据。

6.6 sequenceEqual()
判断两个 Observable 发送的事件是否相同。

Observable.sequenceEqual(Observable.just(1, 2, 3),
Observable.just(1, 2, 3))
.subscribe(new Consumer < Boolean > () {
    @Override
    public void accept(Boolean aBoolean) throws Exception {
        Log.d(TAG, "========================onNext " + aBoolean);
    }
});


05-26 10:11:45.975 14157-14157/? D/chan: ========================onNext true

6.7 contains()
判断事件序列中是否含有某个元素,如果有则返回 true,如果没有则返回 false。

Observable.just(1, 2, 3)
.contains(3)
.subscribe(new Consumer < Boolean > () {
    @Override
    public void accept(Boolean aBoolean) throws Exception {
        Log.d(TAG, "========================onNext " + aBoolean);
    }
});



打印结果:
05-26 10:14:23.522 15085-15085/com.example.rxjavademo D/chan: ========================onNext true

6.8 isEmpty()
判断事件序列是否为空。

Observable.create(new ObservableOnSubscribe < Integer > () {

    @Override
    public void subscribe(ObservableEmitter < Integer > e) throws Exception {
        e.onComplete();
    }
})
.isEmpty()
.subscribe(new Consumer < Boolean > () {
    @Override
    public void accept(Boolean aBoolean) throws Exception {
        Log.d(TAG, "========================onNext " + aBoolean);
    }
});


05-26 10:17:16.725 16109-16109/com.example.rxjavademo D/chan: ========================onNext true

6.9 amb()
amb() 要传入一个 Observable 集合,但是只会发送最先发送事件的 Observable 中的事件,其余 Observable 将会被丢弃。

ArrayList < Observable < Long >> list = new ArrayList < > ();

list.add(Observable.intervalRange(1, 5, 2, 1, TimeUnit.SECONDS));
list.add(Observable.intervalRange(6, 5, 0, 1, TimeUnit.SECONDS));

Observable.amb(list)
.subscribe(new Consumer < Long > () {
    @Override
    public void accept(Long aLong) throws Exception {
        Log.d(TAG, "========================aLong " + aLong);
    }
});



05-26 10:21:29.580 17185-17219/com.example.rxjavademo D/chan: ========================aLong 6
05-26 10:21:30.580 17185-17219/com.example.rxjavademo D/chan: ========================aLong 7
05-26 10:21:31.579 17185-17219/com.example.rxjavademo D/chan: ========================aLong 8
05-26 10:21:32.579 17185-17219/com.example.rxjavademo D/chan: ========================aLong 9
05-26 10:21:33.579 17185-17219/com.example.rxjavademo D/chan: ========================aLong 10

表示只会发送最先加进去的第二个。

6.10 defaultIfEmpty()
如果观察者只发送一个 onComplete() 事件,则可以利用这个方法发送一个值。

Observable.create(new ObservableOnSubscribe < Integer > () {

    @Override
    public void subscribe(ObservableEmitter < Integer > e) throws Exception {
        e.onComplete();
    }
})
.defaultIfEmpty(666)
.subscribe(new Consumer < Integer > () {
    @Override
    public void accept(Integer integer) throws Exception {
        Log.d(TAG, "========================onNext " + integer);
    }
});


05-26 10:26:56.376 19249-19249/com.example.rxjavademo D/chan: ========================onNext 666

至此,RXJAVA常见的使用方式介绍完毕。

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