java - RxJava 2 : BehaviorSubject and Observable. 合并最新问题

Question

我在组合 BehaviorSubject 和 Observable.combineLatest 时遇到一些问题。我能够在(较小的)测试中重现它。这是当前失败的测试:

import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import io.reactivex.Observable;
import io.reactivex.observers.TestObserver;
import io.reactivex.subjects.BehaviorSubject;
import io.reactivex.subjects.Subject;

import static java.util.Collections.singletonList;

public class MyTest {

    @Test
    public void test() {
        Subject<Integer> intSource = BehaviorSubject.createDefault(1);

        Subject<List<Observable<Integer>>> mainSubject = 
            BehaviorSubject.createDefault(singletonList(intSource));

        TestObserver<List<Integer>> testObserver = 
            mainSubject.flatMap(observables ->
                Observable.combineLatest(observables, this::castObjectsToInts)
            )
            .test();

        List<Observable<Integer>> newValue = new ArrayList<>();
        newValue.add(intSource); // same value as before
        newValue.add(Observable.just(2)); // add another value to this list.

        mainSubject.onNext(newValue);

        // intSource was already '1', but this is just to 'update' it.
        intSource.onNext(1); // COMMENT OUT THIS LINE

        testObserver.assertValueAt(0, singletonList(1));
        testObserver.assertValueAt(1, Arrays.asList(1, 2));
        testObserver.assertValueAt(2, Arrays.asList(1, 2)); // COMMENT OUT THIS LINE
        testObserver.assertValueCount(3); // REPLACE 3 WITH 2
    }

    private List<Integer> castObjectsToInts(Object[] objects) {
        List<Integer> ints = new ArrayList<>(objects.length);
        for (Object object : objects) {
            ints.add((Integer) object);
        }
        return ints;
    }
}

(如果用“COMMENT OUT THIS LINE”注释掉这两行，并将最后一个 3 替换为 2，则测试成功。)

为什么这个测试失败了？我没有发现代码有任何问题。

Answer 1

失败是因为您忘记了 mainSubject.flatMap 仍然有第一个 intSource 处于 Activity 状态，因此 intSource.onNext(1) 将首先触发 combineLatest 序列。 testObserver.assertValueAt(2) 将成为 List 中的单个值。 assertValueAt(3) 将包含 1, 2，整个序列有 4 个项目。