Rxjava3使用教程：操作符-过滤

过滤操作符

根据应用场景对过滤操作符进行分类，可分成以下4个类别：

1. 根据"指定条件"过滤事件

操作符	作用
filter	过滤 特定条件的事件
ofType	过滤 特定数据类型的数据
skip/skipLast	跳过某个事件
distinct/distinctUntilChanged	过滤事件序列中重复的事件 / 连续重复的事件

• filter()

  Observable.just("hello", 1, "haha", 2).filter(new Predicate() {
      @Override
      public boolean test(Serializable serializable) throws Throwable {
          return serializable instanceof Integer;
      }
  }).subscribe(observer);
  

  结果：

  2022-05-05 14:59:17.674 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 14:59:17.674 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 14:59:17.675 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:2
  2022-05-05 14:59:17.675 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• ofType()

  Observable.just(1,2,"hello").ofType(String.class).subscribe(observer);
  

  结果：

  2022-05-05 14:58:09.137 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 14:58:09.137 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:hello
  2022-05-05 14:58:09.137 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• skip()

  Observable.just(1,2,3,4,5).skip(2).subscribe(observer);
  

  结果：

  2022-05-05 15:00:10.151 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:00:10.151 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:3
  2022-05-05 15:00:10.151 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:4
  2022-05-05 15:00:10.152 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:5
  2022-05-05 15:00:10.152 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• skipLast()

  Observable.just(1,2,3,4,5).skipLast(3).subscribe(observer);
  

  结果：

  2022-05-05 15:01:03.328 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:01:03.328 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 15:01:03.328 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:2
  2022-05-05 15:01:03.328 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• distinct()

  //过滤事件序列中重复的事件
  Observable.just(1,2,2,4,4,5,6, 1).distinct().subscribe(observer);
  

  结果：

  2022-05-05 15:01:42.336 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:2
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:4
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:5
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:6
  2022-05-05 15:01:42.337 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• distinctUntilChanged()

  //过滤事件序列中连续重复的事件
  Observable.just(1,2,2,4,4,5,6, 1).distinctUntilChanged().subscribe(observer);
  

  结果：

  2022-05-05 15:02:07.275 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:2
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:4
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:5
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:6
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 15:02:07.276 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

2. 根据"指定事件数量"过滤事件

操作符	作用
take	指定观察者最多能接收到的事件数量
takeLast	指定观察者只能接收到被观察者发送的最后几个事件

• take

  Observable.just(1,2,3,4,5).take(2).subscribe(observer);
  

  结果:

  2022-05-05 15:06:45.219 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:06:45.219 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:1
  2022-05-05 15:06:45.219 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:2
  2022-05-05 15:06:45.219 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

• takeLast

  Observable.just(1,2,3,4,5).takeLast(1).subscribe(observer);
  

  结果:

  2022-05-05 15:06:58.362 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe:
  2022-05-05 15:06:58.363 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onNext:5
  2022-05-05 15:06:58.363 1522-1522/com.alsan.rxjavademo D/RxFilterSymbolActivity: onComplete
  

3. 根据"指定时间"过滤事件

操作符	作用
throttleFirst	在某段时间内，只发送该段时间内第1次事件
throttleLast/sample	在某段时间内，只发送该段时间内最后1次事件
throttleWithTimeout / debounce	发送数据事件时，若2次发送事件的间隔＜指定时间，就会丢弃前一次的数据，直到指定时间内都没有新数据发射时才会发送后一次的数据

• throttleFirst

  Observable.create(new ObservableOnSubscribe() {
      @Override
      public void subscribe(ObservableEmitter e) throws Exception {
          // 隔段事件发送时间
          e.onNext(1);
          Thread.sleep(500);
  
          e.onNext(2);
          Thread.sleep(400);
  
          e.onNext(3);
          Thread.sleep(300);
  
          e.onNext(4);
          Thread.sleep(300);
  
          e.onNext(5);
          Thread.sleep(300);
  
          e.onNext(6);
          Thread.sleep(400);
  
          e.onNext(7);
          Thread.sleep(300);
          e.onNext(8);
  
          Thread.sleep(300);
          e.onNext(9);
  
          Thread.sleep(300);
          e.onComplete();
      }
  }).throttleFirst(1, TimeUnit.SECONDS)//每1秒中采用数据
          .subscribe(new Observer() {
              @Override
              public void onSubscribe(Disposable d) {
                  Log.d(TAG, "开始采用subscribe连接");
              }
  
              @Override
              public void onNext(Integer value) {
                  Log.d(TAG, "接收到了事件"+ value  );
              }
  
              @Override
              public void onError(Throwable e) {
                  Log.d(TAG, "对Error事件作出响应");
              }
  
              @Override
              public void onComplete() {
                  Log.d(TAG, "对Complete事件作出响应");
              }
          });
  

  结果：

  2022-05-05 15:27:20.009 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 开始采用subscribe连接
  2022-05-05 15:27:20.009 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件1
  2022-05-05 15:27:21.214 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件4
  2022-05-05 15:27:22.218 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件7
  2022-05-05 15:27:23.121 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 对Complete事件作出响应
  

• throttleLast/sample

  Observable.create(new ObservableOnSubscribe() {
      @Override
      public void subscribe(ObservableEmitter e) throws Exception {
          // 隔段事件发送时间
          e.onNext(1);
          Thread.sleep(500);
  
          e.onNext(2);
          Thread.sleep(400);
  
          e.onNext(3);
          Thread.sleep(300);
  
          e.onNext(4);
          Thread.sleep(300);
  
          e.onNext(5);
          Thread.sleep(300);
  
          e.onNext(6);
          Thread.sleep(400);
  
          e.onNext(7);
          Thread.sleep(300);
          e.onNext(8);
  
          Thread.sleep(300);
          e.onNext(9);
  
          Thread.sleep(300);
          e.onComplete();
      }
  }).throttleLast(1, TimeUnit.SECONDS)//每1秒中采用数据
          .subscribe(new Observer() {
              @Override
              public void onSubscribe(Disposable d) {
                  Log.d(TAG, "开始采用subscribe连接");
              }
  
              @Override
              public void onNext(Integer value) {
                  Log.d(TAG, "接收到了事件"+ value  );
              }
  
              @Override
              public void onError(Throwable e) {
                  Log.d(TAG, "对Error事件作出响应");
              }
  
              @Override
              public void onComplete() {
                  Log.d(TAG, "对Complete事件作出响应");
              }
          });
  

  结果：

  2022-05-05 15:27:23.124 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 开始采用subscribe连接
  2022-05-05 15:27:24.129 3744-3924/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件3
  2022-05-05 15:27:25.129 3744-3924/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件6
  2022-05-05 15:27:26.129 3744-3924/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件9
  2022-05-05 15:27:26.234 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 对Complete事件作出响应
  

• throttleWithTimeout/debounce

  Observable.create(new ObservableOnSubscribe() {
              @Override
              public void subscribe(ObservableEmitter e) throws Exception {
                  // 隔段事件发送时间
                  e.onNext(1);
                  Thread.sleep(500);
                  e.onNext(2); // 1和2之间的间隔小于指定时间1s，所以前1次数据（1）会被抛弃，2会被保留
                  Thread.sleep(1500);  // 因为2和3之间的间隔大于指定时间1s，所以之前被保留的2事件将发出
                  e.onNext(3);
                  Thread.sleep(1500);  // 因为3和4之间的间隔大于指定时间1s，所以3事件将发出
                  e.onNext(4);
                  Thread.sleep(500); // 因为4和5之间的间隔小于指定时间1s，所以前1次数据（4）会被抛弃，5会被保留
                  e.onNext(5);
                  Thread.sleep(500); // 因为5和6之间的间隔小于指定时间1s，所以前1次数据（5）会被抛弃，6会被保留
                  e.onNext(6);
                  Thread.sleep(1500); // 因为6和Complete实践之间的间隔大于指定时间1s，所以之前被保留的6事件将发出
  
                  e.onComplete();
              }
          }).throttleWithTimeout(1, TimeUnit.SECONDS)//每1秒中采用数据
                  .subscribe(new Observer() {
                      @Override
                      public void onSubscribe(Disposable d) {
  
                      }
  
                      @Override
                      public void onNext(Integer value) {
                          Log.d(TAG, "接收到了事件"+ value  );
                      }
  
                      @Override
                      public void onError(Throwable e) {
                          Log.d(TAG, "对Error事件作出响应");
                      }
  
                      @Override
                      public void onComplete() {
                          Log.d(TAG, "对Complete事件作出响应");
                      }
                  });
  

  结果：

  2022-05-05 15:21:14.416 3428-3490/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件2
  2022-05-05 15:21:15.916 3428-3490/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件3
  2022-05-05 15:21:18.420 3428-3490/com.alsan.rxjavademo D/RxFilterSymbolActivity: 接收到了事件6
  2022-05-05 15:21:18.920 3428-3428/com.alsan.rxjavademo D/RxFilterSymbolActivity: 对Complete事件作出响应
  

4. 根据"指定事件位置"过滤事件

操作符	作用
firstElement	仅选取第1个元素
lastElement	仅选取最后一个元素
elementAt	指定接收某个元素（通过 索引值 确定）
elementAtOrError	在elementAt（）的基础上，当出现越界情况（即获取的位置索引 ＞ 发送事件序列长度）时，即抛出异常

• firstElement

  Observable.just("hello", 1, "haha", 2).firstElement().subscribe((Consumer) serializable -> {
      Log.d(TAG, serializable.toString());
  });
  

  结果：

  2022-05-05 15:38:09.536 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: hello
  

• lastElement

  Observable.just("hello", 1, "haha", 2).lastElement().subscribe((Consumer) serializable -> {
    Log.d(TAG, serializable.toString());
  });
  

  结果：

  2022-05-05 15:38:22.242 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: 2
  

• elementAt

  Observable.just(1,2,2,4,4,5,6, 1).elementAt(1).subscribe(new Consumer() {
      @Override
      public void accept(Integer integer) throws Throwable {
          Log.d(TAG, "accept:" + integer);
      }
  });
  

  结果：

  2022-05-05 15:39:14.759 3744-3744/com.alsan.rxjavademo D/RxFilterSymbolActivity: accept:2
  

• elementAtOrError

  Observable.just(1,2,3,4,5).elementAtOrError(9).subscribe(new SingleObserver() {
      @Override
      public void onSubscribe(@NonNull Disposable d) {
          Log.d(TAG, "onSubscribe...");
      }
  
      @Override
      public void onSuccess(@NonNull Integer integer) {
          Log.d(TAG, "onSuccess..." + integer);
      }
  
      @Override
      public void onError(@NonNull Throwable e) {
          Log.d(TAG, "onError:" + Log.getStackTraceString(e));
      }
  });
  

  结果：

  022-05-05 15:41:16.713 4285-4285/com.alsan.rxjavademo D/RxFilterSymbolActivity: onSubscribe...
  2022-05-05 15:41:16.715 4285-4285/com.alsan.rxjavademo D/RxFilterSymbolActivity: onError:java.util.NoSuchElementException
          at io.reactivex.rxjava3.internal.operators.observable.ObservableElementAtSingle$ElementAtObserver.onComplete(ObservableElementAtSingle.java:115)
          at io.reactivex.rxjava3.internal.operators.observable.ObservableFromArray$FromArrayDisposable.run(ObservableFromArray.java:112)
          at io.reactivex.rxjava3.internal.operators.observable.ObservableFromArray.subscribeActual(ObservableFromArray.java:38)
          at io.reactivex.rxjava3.core.Observable.subscribe(Observable.java:13095)
          at io.reactivex.rxjava3.internal.operators.observable.ObservableElementAtSingle.subscribeActual(ObservableElementAtSingle.java:37)
          at io.reactivex.rxjava3.core.Single.subscribe(Single.java:4813)
          at com.alsan.rxjavademo.RxFilterSymbolActivity.lambda$onCreate$17$RxFilterSymbolActivity(RxFilterSymbolActivity.java:311)
          at com.alsan.rxjavademo.-$$Lambda$RxFilterSymbolActivity$bbHK8cGk2DGgxkmEzj5endgLd8A.onClick(Unknown Source:2)
          at android.view.View.performClick(View.java:6291)
          at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:967)
          at android.view.View$PerformClick.run(View.java:24931)
          at android.os.Handler.handleCallback(Handler.java:808)
          at android.os.Handler.dispatchMessage(Handler.java:101)
          at android.os.Looper.loop(Looper.java:166)
          at android.app.ActivityThread.main(ActivityThread.java:7529)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)