RxJava常用操作符

• 创建

  • unsafeCreate(create)
    创建一个Observable（被观察者），当被观察者（Observer）/订阅者（Subscriber）
    subscribe(订阅)的时候就会依次发出三条字符串数据（"Hello","RxJava","Nice to meet you"）
    最终onComplete

Observable.unsafeCreate(new Observable.OnSubscribe() {
            @Override
            public void call(Subscriber subscriber) {
                subscriber.onNext("Hello");
                subscriber.onNext("RxJava");
                subscriber.onNext("Nice to meet you");
                subscriber.onCompleted();
            }
        });

• just
  作用同上，订阅时依次发出三条数据，不过此方法参数可以有1-9条

Observable.just("Hello", "RxJava", "Nice to meet you")

• from
  作用同just不过是把参数封装成数组或者可迭代的集合在依次发送出来，突破了just9个参数的限制

String[] strings = {"Hello", "RxJava", "Nice to meet you"};
Observable.from(strings)
        .subscribe(new Action1() {
            @Override
            public void call(String s) {
                System.out.println("onNext--> " + s);
            }
        }, new Action1() {
            @Override
            public void call(Throwable throwable) {
                System.out.println("onError--> " + throwable.getMessage());
            }
        }, new Action0() {
            @Override
            public void call() {
                System.out.println("onComplete");
            }
        });

• defer
  顾名思义，延迟创建

private String[] strings1 = {"Hello", "World"};
    private String[] strings2 = {"Hello", "RxJava"};

    private void test() {
        Observable observable = Observable.defer(new Func0>() {
            @Override
            public Observable call() {
                return Observable.from(strings1);
            }
        });

        strings1 = strings2; //订阅前把strings给改了
        observable.subscribe(new Action1() {
            @Override
            public void call(String s) {
                System.out.println("onNext--> " + s);
            }
        }, new Action1() {
            @Override
            public void call(Throwable throwable) {
                System.out.println("onError--> " + throwable.getMessage());
            }
        }, new Action0() {
            @Override
            public void call() {
                System.out.println("onComplete");
            }
        });
    }

我们发现数据结果变成这样了

onNext--> Hello
onNext--> RxJava
onComplete

由此可以证明defer操作符起到的不过是一个“预创建”的作用，真正创建是发生在订阅的时候

• empty
  创建一个空的，不会发射任何事件（数据）的Observable

Observable.empty()
        .subscribe(new Action1