RxJava之flatMap系列转换操作符

2022-12-19 13:27:47 浏览数 (1)

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转换相关的操作符 以及 官方介绍

RxJava 之 flatMap 系列 转换操作符 官方介绍 ：Transforming Observables

  • flatMap
  • flatMapCompletable
  • flatMapIterable
  • flatMapMaybe
  • flatMapObservable
  • flatMapPublisher
  • flatMapSingle
  • flatMapSingleElement

以下介绍我们就直接具体实现，中间流程请参考 RxJava之create操作符源码解析。

flatMap

官方示例：

代码语言：javascript复制
Observable.just("A", "B", "C")
    .flatMap(new Function<String, ObservableSource<?>>() {
        @Override
        public ObservableSource<?> apply(final String a) throws Exception {
            return Observable.intervalRange(1, 3, 0, 1, TimeUnit.SECONDS)
                    .map(new Function<Long, String>() {
                        @Override
                        public String apply(Long b) throws Exception {
                            return '('   a   ", "   b   ')';
                        }
                    });
        }
    })
    .blockingSubscribe(new Consumer<Object>() {
        @Override
        public void accept(Object o) throws Exception {
            System.out.println(o);
        }
    });

输出：

代码语言：javascript复制
(A, 1)
(B, 1)
(C, 1)
(C, 2)
(B, 2)
(A, 2)
(A, 3)
(B, 3)
(C, 3)

返回对象的 ObservableFlatMap 的 subscribeActual 方法：

代码语言：javascript复制
public void subscribeActual(Observer<? super U> t) {
    if (ObservableScalarXMap.tryScalarXMapSubscribe(source, t, mapper)) {
        return;
    }
    source.subscribe(new MergeObserver<T, U>(t, mapper, delayErrors, maxConcurrency, bufferSize));
}

MergeObserver 的 onNext 方法：

代码语言：javascript复制
public void onNext(T t) {
    // safeguard against misbehaving sources
    ...
    subscribeInner(p);
}

void subscribeInner(ObservableSource<? extends U> p) {
    for (;;) {
        if (p instanceof Callable) {
           ...
                    drain();
           ...
        } else {
            InnerObserver<T, U> inner = new InnerObserver<T, U>(this, uniqueId  );
            if (addInner(inner)) {
                p.subscribe(inner);
            }
            break;
        }
    }
}

InnerObserver 的 onNext 方法：

代码语言：javascript复制
public void onNext(U t) {
    if (fusionMode == QueueDisposable.NONE) {
        parent.tryEmit(t, this);
    } else {
        parent.drain();
    }
}

MergeObserver 的 drain() 方法：

代码语言：javascript复制
void drain() {
    if (getAndIncrement() == 0) {
        drainLoop();
    }
}

void drainLoop() {
    final Observer<? super U> child = this.downstream;//1.0
    int missed = 1;
    for (;;) {
        ...
        SimplePlainQueue<U> svq = queue;
        if (svq != null) {
            for (;;) {
                ...
                U o = svq.poll();
                if (o == null) {
                    break;
                }
                child.onNext(o);//1.1
            }
        }
        ...
        if (d && (svq == null || svq.isEmpty()) && n == 0 && nSources == 0) {
            Throwable ex = errors.terminate();
            if (ex != ExceptionHelper.TERMINATED) {
                if (ex == null) {
                    child.onComplete();//1.2
                } else {
                    child.onError(ex);//1.3
                }
            }
            return;
        }
        ...
    }
}

最终还是调用了 传进来的 observer 的 对应方法。

flatMapCompletable

官方示例：

代码语言：javascript复制
Observable<Integer> source = Observable.just(2, 1, 3);
Completable completable = source.flatMapCompletable(new Function<Integer, CompletableSource>() {
    @Override
    public CompletableSource apply(final Integer x) throws Exception {
        return Completable.timer(x, TimeUnit.SECONDS)
                .doOnComplete(new Action() {
                    @Override
                    public void run() throws Exception {
                        System.out.println("Info: Processing of item ""   x   "" completed");
                    }
                });
    }
});
completable.doOnComplete(
        new Action() {
            @Override
            public void run() throws Exception {
                System.out.println("Info: Processing of all items completed");
            }
        })
        .blockingAwait();

输出：

代码语言：javascript复制
Info: Processing of item "1" completed
Info: Processing of item "2" completed
Info: Processing of item "3" completed
Info: Processing of all items completed
flatMapIterable

官方示例：

代码语言：javascript复制
Observable.just(1, 2, 3, 4)
        .flatMapIterable(new Function<Integer, Iterable<?>>() {
            @Override
            public Iterable<?> apply(Integer integer) throws Exception {
                switch (integer % 4) {
                    case 1:
                        return Arrays.asList("A");
                    case 2:
                        return Arrays.asList("B", "B");
                    case 3:
                        return Arrays.asList("C", "C", "C");
                    default:
                        return Arrays.asList();
                }
            }
        })
        .subscribe(new Consumer<Object>() {
            @Override
            public void accept(Object o) throws Exception {
                System.out.println(o);
            }
        });

输出：

代码语言：javascript复制
A
B
B
C
C
C
flatMapMaybe

官方示例：

代码语言：javascript复制
Observable.just(9.0, 16.0, -4.0)
        .flatMapMaybe(new Function<Double, MaybeSource<?>>() {
            @Override
            public MaybeSource<?> apply(Double x) throws Exception {
                if (x.compareTo(0.0) < 0) {
                    return Maybe.empty();
                } else {
                    return Maybe.just(Math.sqrt(x));
                }
            }
        })
        .subscribe(new Observer<Object>() {
            @Override
            public void onSubscribe(Disposable d) {

            }

            @Override
            public void onNext(Object o) {
                System.out.println(o);
            }

            @Override
            public void onError(Throwable e) {
                e.printStackTrace();
            }

            @Override
            public void onComplete() {
                System.out.println("onComplete");
            }
        });

输出：

代码语言：javascript复制
3.0
4.0
onComplete
flatMapObservable

官方示例：

代码语言：javascript复制
Single<String> source = Single.just("Kirk, Spock, Chekov, Sulu");
Observable<String> names = source.flatMapObservable(new Function<String, ObservableSource<? extends String>>() {
    @Override
    public ObservableSource<? extends String> apply(String text) throws Exception {
        return Observable.fromArray(text.split(","))
                .map(new Function<String, String>() {
                    @Override
                    public String apply(String s) throws Exception {
                        return s;
                    }
                });
    }
});
names.subscribe(new Consumer<String>() {
    @Override
    public void accept(String name) throws Exception {
        System.out.println("onNext: "   name);
    }
});

输出：

代码语言：javascript复制
onNext: Kirk
onNext:  Spock
onNext:  Chekov
onNext:  Sulu
flatMapPublisher

官方示例：

代码语言：javascript复制
Single<String> source = Single.just("Kirk, Spock, Chekov, Sulu");
Flowable<String> names = source.flatMapPublisher(new Function<String, Publisher<? extends String>>() {
    @Override
    public Publisher<? extends String> apply(String text) throws Exception {
        return Flowable.fromArray(text.split(","))
                .map(new Function<String, String>() {
                    @Override
                    public String apply(String s) throws Exception {
                        return s;
                    }
                });
    }
});
names.subscribe(new Consumer<String>() {
    @Override
    public void accept(String name) throws Exception {
        System.out.println("onNext: "   name);
    }
});

输出：

代码语言：javascript复制
onNext: Kirk
onNext:  Spock
onNext:  Chekov
onNext:  Sulu
flatMapSingle

官方示例：

代码语言：javascript复制
Observable.just(4, 2, 1, 3)
        .flatMapSingle(new Function<Integer, SingleSource<?>>() {
            @Override
            public SingleSource<?> apply(final Integer integer) throws Exception {
                return Single.timer(integer, TimeUnit.SECONDS)
                        .map(new Function<Long, Object>() {
                            @Override
                            public Object apply(Long aLong) throws Exception {
                                return integer;
                            }
                        });
            }
        })
        .blockingSubscribe(new Consumer<Object>() {
            @Override
            public void accept(Object o) throws Exception {
                System.out.println(o);
            }
        });

输出：

代码语言：javascript复制
1
2
3
4
flatMapSingleElement

官方示例：

代码语言：javascript复制
Maybe<Integer> source = Maybe.just(-42);
Maybe<Integer> result = source.flatMapSingleElement(new Function<Integer, SingleSource<? extends Integer>>() {
    @Override
    public SingleSource<? extends Integer> apply(Integer x) throws Exception {
        return Single.just(Math.abs(x));
    }
});

result.subscribe(new Consumer<Integer>() {
    @Override
    public void accept(Integer integer) throws Exception {
        System.out.println(integer);
    }
});

输出：

代码语言：javascript复制
42

以上

android

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