序列有很多种类，用对了序列就会有事半功倍的效果。这个篇章总结一下常用序列的创建：

1.emty

空序列创建

Observable<String>.empty()
.subscribe(onNext: { (text) in
    print(text)
}

2.just

单个信号序列创建

Observable<[String]>.just(["a","b","c"])
.subscribe(onNext: { (text) in
    print(text)
}

3.of

多个元素

Observable<String>.of("a","b")
.subscribe(onNext: { (text) in
    print(text)
}
Observable<[String]>.of(["a","b"])
.subscribe(onNext: { (text) in
    print(text)
}
Observable<[String: String]>.of(["a": "1", "b": "2"])
.subscribe(onNext: { (text) in
    print(text)
}

4.from

从集合中获取序列，可选项处理更安全

Observable<[String]>.from(optional: ["a","b"])
.subscribe(onNext: { (text) in
    print(text)
}

5.deferred

deferred延迟序列的初始化，通过传入的闭包来实现初始化

var isTrue = true
Observable<String>.deferred { () -> Observable<String> in
      if isTrue {
          return Observable.of("1","2")
      }
      return Observable.of("a","b")
}.subscribe(onNext: { (text) in
    print(text)
}

6.range

生成指定范围内的可观察整数序列

Observable.range(start: 1, count: 5)
.subscribe(onNext: { (num) in
    print(num)
}

7.range

只有当所有的判断条件都符合的时候，才会响应的序列。会先判断条件1，再判断条件2，然后一直递归下去，直到有条件不满足

Observable.generate(initialState: 0,                // 初始值
                            condition: { $0 < 8},  // 条件1
                            iterate: { $0 + 1 })    // 条件2
.subscribe(onNext: { (num) in
    print(num)
}

8.repeatElement

可以无限发出给定元素的序列

Observable<Int>.repeatElement(5)
.subscribe(onNext: { (num) in
    print(num)
}

9.error

错误序列

Observable<String>.error(NSError.init(domain: "err", code: 888, userInfo: nil))
.subscribe(onError: { (err) in
    print(err)
})

10.never

永远不会发送事件也不会终止的序列

Observable<String>.never()
.subscribe(onNext: { (num) in
    print(num)
}

11.create

基础序列

Observable<String>.create{observer in
    observer.onNext("发送")
    observer.onCompleted()
    return Disposables.create()
}.subscribe(onNext: { (text) in
    print(text)
}

12.timer

定时器

Observable<Int>.timer(1, scheduler: MainScheduler.instance)
.subscribe(onNext: { (num) in
    print(num)
}

13.interval

定时器

Observable<Int>.interval(1, scheduler: MainScheduler.instance)
.subscribe(onNext: { (num) in
    print(num)
}