创建型操作符

创建型操作符

• create
• from
• just
• defer
• timer
• interval
• range
• repeat/repeatWhen

create操作符

create操作符是所有创建型操作符的“根”，也就是说其他创建型操作符最后都是通过create操作符来创建Observable的.

Observable.create(new Observable.OnSubscribe() {
        @Override
        public void call (Subscriber observer){
            try {
                if (!observer.isUnsubscribed()) {
                    for (int i = 1; i < 5; i++) {
                        observer.onNext(i);
                    }
                    observer.onCompleted();
                }
            } catch (Exception e) {
                observer.onError(e);
            }
        }
    }).subscribe(new Subscriber() {
        @Override 
        public void onNext (Integer item){
            System.out.println("Next: " + item);
        }
        @Override 
        public void onError (Throwable error){
            System.err.println("Error: " + error.getMessage());
        }
        @Override 
        public void onCompleted () {
            System.out.println("Sequence complete.");
        }
    });

运行结果如下：
Next: 1
Next: 2
Next: 3
Next: 4
Sequence complete.

---

from操作符

from操作符是把其他类型的对象和数据类型转化成Observable

Integer[] items = { 0, 1, 2, 3, 4, 5 };
Observable myObservable = Observable.from(items);

myObservable.subscribe(
    new Action1() {
        @Override
        public void call(Integer item) {
            System.out.println(item);
        }
    },
    new Action1() {
        @Override
        public void call(Throwable error) {
            System.out.println("Error encountered: " + error.getMessage());
        }
    },
    new Action0() {
        @Override
        public void call() {
            System.out.println("Sequence complete");
        }
    }
);

运行结果如下：
Next: 1
Next: 2
Next: 3
Next: 4
Sequence complete.

---

just操作符

just操作符也是把其他类型的对象和数据类型转化成Observable，它和from操作符很像，只是方法的参数有所差别

Observable.just(1, 2, 3)
          .subscribe(new Subscriber() {
        @Override
        public void onNext(Integer item) {
            System.out.println("Next: " + item);
        }

        @Override
        public void onError(Throwable error) {
            System.err.println("Error: " + error.getMessage());
        }

        @Override
        public void onCompleted() {
            System.out.println("Sequence complete.");
        }
    });

运行结果如下：
Next: 1
Next: 2
Next: 3
Sequence complete.

---

defer操作符

defer操作符是直到有订阅者订阅时，才通过Observable的工厂方法创建Observable并执行，defer操作符能够保证Observable的状态是最新的.

// 下面通过比较defer操作符和just操作符的运行结果作比较：
        i=10;
        Observable justObservable = Observable.just(i);
        i=12;
        Observable deferObservable = Observable.defer(new Func0>() {
            @Override
            public Observable