RxSwift基本使用（一）

备注：本文参考自田腾飞博文 [RxSwift入坑解读-你所需要知道的各种概念] (http://www.codertian.com/2016/11/27/RxSwift-ru-keng-ji-read-document/)，出于个人学习以及笔记需要特记录下RxSwift基本使用

概念

Observable : 可被观察的，事件源

Observer : 观察者，观察者需要订阅Observable，才能受到其发出的事件

DisposeBag : 相当于iOS中的ARC，会在适当的时候销毁观察者，自动去释放资源

如果需要手动销毁观察者直接调用dispose()方法,例： 
Observable.empty().subscribe { (str:Event) in 
print(“empty:”,str) 
}.dispose()

subscribe : 订阅者，用于订阅sequence发出的事件

基本使用

never

never就是创建一个sequence,但不发出任何事件信号

let bag = DisposeBag()
Observable.never().subscribe { (str :Event<String>) in
    print("never:",str) //无
}.addDisposableTo(bag)

备注：为了方便简洁，后续例子中创建bag变量的代码将省略

empty

empty创建一个空的sequence,但只能发出一个completed事件

Observable.empty().subscribe { (str :Event<String>) in
    print("empty:",str)
}.addDisposableTo(bag)

//empty: completed

just

just创建一个sequence,但只能发出一种特定的事件，能正常结束

Observable.just("just").subscribe { (str :Event<String>) in
    print("just:",str)
}.addDisposableTo(bag)

//just:next(just)
//just:completed

of

创建一个sequence能发出很多种事件信号

Observable.of("1","2","3").subscribe { (str) in
    print("of:",str)
}.addDisposableTo(bag)

    /**
    of: next(1)
    of: next(2)
    of: next(3)
    of: completed
    */

   //subscribe onNext 直接取值

    Observable.of("1","2","3").subscribe(onNext: { (str) in
        print("of2:",str)
    }).addDisposableTo(bag)

    /**
     of2: 1
     of2: 2
     of2: 3
     */

from

from从集合中创建sequence，例如数组，字典或者Set

    Observable.from([10,100,1000]).subscribe(onNext: { (num) in
        print("from:",num)
    }).addDisposableTo(bag)

    /**
     from: 10
     from: 100
     from: 1000
     **/

create

create 自定义可观察的sequence

    //create 自定义可观察的sequence
    let myObservable = Observable.create { (observer:AnyObserver<Any>) -> Disposable in
        observer.onNext("12")
        observer.onNext("21")
        observer.onNext("123")
        observer.onCompleted()
        return Disposables.create()
    }
    myObservable.subscribe { (e:Event<Any>) in
        print("myObservable:",e)
        }.addDisposableTo(bag)

    /**
     myObservable: next(12)
     myObservable: next(21)
     myObservable: next(123)
     myObservable: completed
     **/

range

range 创建一个sequence，会发出这个范围中所有事件

    Observable.range(start: 1, count: 5).subscribe(onNext: { (num) in
        print("range:",num)
    }).addDisposableTo(bag)
    /**
     range: 1
     range: 2
     range: 3
     range: 4
     range: 5
     **/

repeatElement

创建一个sequence，发出特定的事件n次

Observable.repeatElement("LouKit").take(3).subscribe { print($0)}.addDisposableTo(bag)

    //重复发出3次，如果没有take 就无限次
    /**
     next(LouKit)
     next(LouKit)
     next(LouKit)
     completed
     **/

generate

generate是创建一个可观察sequence，当初始化的条件为true的时候，他就会发出所对应的事件

    Observable.generate(initialState: 10, condition: {$0 < 15}, iterate: {$0 + 1}).subscribe(onNext: {print("generate",$0)}).addDisposableTo(bag)
    /**
     generate 10
     generate 11
     generate 12
     generate 13
     generate 14
     **/

deferred

deferred会为每一为订阅者observer创建一个新的可观察序列

    var index = 1
    let deferred = Observable<String>.deferred{

        print("index:",index)
        index += 1

        return Observable.create{ observer in
            observer.onNext("1")
            observer.onNext("2")
            observer.onCompleted()
            return Disposables.create()
        }
    }

    deferred.subscribe { print("调用1:",$0)}.addDisposableTo(bag)

    deferred.subscribe { print("调用2:",$0)}.addDisposableTo(bag)

    /**
     index: 1
     调用1: next(1)
     调用1: next(2)
     调用1: completed
     index: 2
     调用2: next(1)
     调用2: next(2)
     调用2: completed
     **/

do

主要用于在subscribe中onNext，onError，onCompleted前调用

    Observable.just("00").do(onNext: {print("doOnNext:",$0)},onError: {print("doOnError:",$0)},onCompleted: {print("doOnCompleted:")})
        .subscribe(onNext: { (str) in
            print("onNext:",str)
        }, onError: { (error) in
            print("onError")
        }, onCompleted: {
            print("onCompleted")
        }).addDisposableTo(bag)

    /**
     doOnNext: 00
     onNext: 00
     doOnCompleted:
     onCompleted
     **/

Subjects

Subjet是observable和Observer之间的桥梁，一个Subject既可以充当Obserable也可以充当Observer，即它可以发出事件，也可以监听事件

PublishSubject

采用PublishSubject订阅事件的时候，只能接收到订阅他之后发生的事件

    let publicSubject = PublishSubject<String>()
    publicSubject.onNext("A")
    publicSubject.onNext("B")
    publicSubject.subscribe(onNext: {print("publicSubject:",$0)}) .addDisposableTo(bag)
    publicSubject.onNext("C")
    publicSubject.onNext("D")

    /**
     publicSubject: C
     publicSubject: D
     **/

ReplaySubject

可以接收到订阅他之后以及之前发生的事件,对于要接受几个以前的事件取决于bufferSize设置的大小

    let replaySubject = ReplaySubject<String>.create(bufferSize: 2)
    replaySubject.onNext("A")
    replaySubject.onNext("B")
    replaySubject.onNext("C")
    replaySubject.onNext("D")
    replaySubject.subscribe(onNext: {print("replaySubject:",$0)}) .addDisposableTo(bag)
    replaySubject.onNext("E")
    replaySubject.onNext("F")
    replaySubject.onNext("G")
    /**
     replaySubject: C
     replaySubject: D
     replaySubject: E
     replaySubject: F
     replaySubject: G
     **/

    //接受全部的事件
    let replaySubject2 = ReplaySubject<String>.createUnbounded()
    replaySubject2.onNext("A")
    replaySubject2.onNext("B")
    replaySubject2.subscribe(onNext: {print("replaySubject2:",$0)}) .addDisposableTo(bag)
    replaySubject2.onNext("E")
    replaySubject2.onNext("F")

    /**
     replaySubject2: A
     replaySubject2: B
     replaySubject2: E
     replaySubject2: F
     **/

BehaviorSubject

采用BehaviorSubject订阅事件，会接收到订阅之前的最后一个事件以及订阅之后所有事件。

    let behavior = BehaviorSubject(value: "behavior")
    behavior.onNext("A")
    behavior.onNext("B")
    behavior.subscribe(onNext: {print("behavior:",$0)}).addDisposableTo(bag)
    behavior.onNext("C")
    behavior.onNext("D")

    /**
     behavior: B
     behavior: C
     behavior: D
     **/

Variable

Variable是对BehaviorSubject一个包装；

Variable当成Obserable, 让订阅者进行订阅时, 需要asObserable转成Obserable；

Variable发出事件, 直接修改对象的value即可;

当事件结束时,Variable会自动发出completed事件

    let variable = Variable("variable")

    variable.value = "A"
    variable.value = "B"
    variable.asObservable().subscribe { (event:Event<String>) in
        print("variable:",event)
        }.addDisposableTo(bag)
    variable.value = "C"
    variable.value = "D"

    /**
     variable: next(B)
     variable: next(C)
     variable: next(D)
     variable: completed
     **/

联合操作

联合操作就是把多个Observable流合成单个Observable流

startWith

在发出事件消息之前，先发出某个特定的事件消息。

    Observable.of(1,2).startWith(3).subscribe(onNext: {print($0)}).addDisposableTo(bag)

    /**
     3
     1
     2
     **/

merge

将多个Observable流合成单个Observable流，然后任何一个Observable发出事件都能被接收到

    let sub1 = PublishSubject<String>()
    let sub2 = PublishSubject<String>()

    Observable.of(sub1,sub2).merge().subscribe(onNext: { print($0) }).addDisposableTo(bag)
    sub1.onNext("sub1-1")
    sub1.onNext("sub1-2")

    sub2.onNext("sub2-1")
    sub1.onNext("sub1-2")
    sub2.onNext("sub2-2")
    /**
     sub1-1
     sub1-2
     sub2-1
     sub1-2
     sub2-2
     **/

zip

将多个Observable流合成单个Observable流，只有当多个Observable流同时发出事件时，并且把多个Observable流的内容合并成一个元组，才会触发压缩流的事件。

    let zip1 = PublishSubject<String>()
    let zip2 = PublishSubject<String>()

    Observable.zip(zip1,zip2){ zip1,zip2 in
        "\(zip1) \(zip2)"
        }.subscribe(onNext: { print($0) })
        .addDisposableTo(bag)

    zip1.onNext("zip1-1")
    zip1.onNext("zip1-2")
    zip2.onNext("zip2-1")
    zip2.onNext("zip2-2")

    /**
     zip1-1 zip2-1
     zip1-2 zip2-2
     **/

注意：merge、zip都能将多个Observable流合成单个Observable流，但合并后前者任何一个Observable发出事件都能被接收到，后者必须是多个流同时发出事件时才被接收到

combineLatest

将多个Observable流合并起来 并拿到其各个流的最新值,即每个合并的signal至少都有过一次onNext，才会触发合并的流

    let ps1 = PublishSubject<String>()
    let ps2 = PublishSubject<String>()

    Observable.combineLatest(ps1, ps2) { element1, element2 in
        "\(element1) \(element2)"
        }
        .subscribe(onNext: { print($0) })
        .addDisposableTo(bag)

    ps1.onNext("ps1-01")
    ps1.onNext("ps1-02")
    ps2.onNext("ps2-01")

    /**
     ps1-02 ps2-01
     **/

switchLatest

用于对事件流进行转换，即一个Observable中的内容还是Observable。(个人理解)

    let bs1 = BehaviorSubject(value: "1")
    let bs2 = BehaviorSubject(value: "A")

    let variable = Variable(bs1)
    variable.asObservable().switchLatest().subscribe(onNext: {print($0)}).addDisposableTo(bag)
    bs1.onNext("2")
    variable.value = bs2
    bs1.onNext("3")
    bs2.onNext("B")
    /**
     1
     2
     A
     B
     **/