flatMap、flatMapLatest

flatMap

将一个sequence转换为一个sequences，当你接收一个sequence的事件，你还想接收其他sequence发出的事件的话可以使用flatMap，她会将每一个sequence事件进行处理以后，然后再以一个sequence形式发出事件

let stu1 = Student(score: Variable(80))
let stu2 = Student(score: Variable(100))
        
let student = Variable(stu1)
student.asObservable().flatMap { (stu: Student) -> Observable<Double> in
    return stu.score.asObservable()
}.subscribe { (event) in
    print(event)
}.addDisposableTo(bag)
        
student.value = stu2
stu1.score.value = 10
stu2.score.value = 20
        
    /* 输出顺序为:
         next(80.0)
         next(100.0)
         next(10.0)
         next(20.0)
         completed
     */

flatMapLatest

flatMapLatest只会接收最新的value事件，将上例代码改为flatMapLatest

let stu3 = Student(score: Variable(70))
let stu4 = Student(score: Variable(60))
 
let student1 = Variable(stu3)
student1.asObservable().flatMapFirst { (stu) -> Observable<Double> in
    return stu.score.asObservable()
}.subscribe { (event: Event<Double>) in
    print(event)
}.addDisposableTo(bag)
student1.value = stu4
stu3.score.value = 10
stu4.score.value = 20
        
    /* 输出顺序为:
         next(70.0)
         next(10.0)
         completed
     */