RxJava2 Flowable last

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最新推荐文章于 2023-01-05 18:14:12 发布

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分类专栏： rxjava2 文章标签： last

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本文详细解析了RxJava中Flowable的last、lastElement及lastOrError操作符的功能与使用。通过实例展示了如何获取Flowable序列中的最后一个元素，以及在序列为空时的不同处理方式。

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1 接口

2 图解和说明

3 测试用例

1 接口

Single<T>

last(T defaultItem)

Returns a Single that emits only the last item emitted by this Flowable, or a default item if this Flowable completes without emitting any items.

返回仅发出此Flowable发出的最后一项的Single，如果此Flowable完成而不发出任何项，则返回默认项。

Maybe<T>

lastElement()

Returns a Maybe that emits the last item emitted by this Flowable or completes if this Flowable is empty.

返回一个Maybe，它发出此Flowable发出的最后一项，或者如果此Flowable为空则完成。

Single<T>

lastOrError()

Returns a Single that emits only the last item emitted by this Flowable or signals a NoSuchElementException if this Flowable is empty.

返回一个Single，它仅发出此Flowable发出的最后一项，或者如果此Flowable为空则发出NoSuchElementException信号。

2 图解和说明

3 测试用例

 @Test
    public void last() {
        System.out.println("------> last");
        Flowable.just("one","two","three").last("is empty").subscribe(new SingleObserver<Object>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(Object value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:" + e.getMessage().toString());
            }
        });

        Flowable.empty().last("is empty").subscribe(new SingleObserver<Object>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(Object value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:" + e.getMessage().toString());
            }
        });

        System.out.println("------> lastElement");
        Flowable.just("one","two","three").lastElement().subscribe(new MaybeObserver<String>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(String value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:" + e.getMessage().toString());
            }

            @Override
            public void onComplete() {

            }
        });

        Flowable.empty().lastElement().subscribe(new MaybeObserver<Object>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(Object value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:" + e.getMessage().toString());
            }

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


        System.out.println("------> lastOrError");
        Flowable.just("one","two","three").lastOrError().subscribe(new SingleObserver<Object>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(Object value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:" + e.getMessage().toString());
            }
        });

        Flowable.empty().lastOrError().subscribe(new SingleObserver<Object>() {
            @Override
            public void onSubscribe(Disposable d) {
            }

            @Override
            public void onSuccess(Object value) {
                System.out.println("onSuccess:" + value.toString());
            }

            @Override
            public void onError(Throwable e) {
                System.out.println("onError:");
            }
        });


    }



------> last
onSuccess:three
onSuccess:is empty
------> lastElement
onSuccess:three
onComplete
------> lastOrError
onSuccess:three
onError: