首先，我們先來看看Swift中創建Timer的幾種方式

1.Timer的方式

• target action

timer = Timer.init(timeInterval: 1, target: self, selector: #selector(timerFire), userInfo: nil, repeats: true) RunLoop.current.add(timer, forMode: .common)


@objc func timerFire() {
   print("走你")
}

這種方式在設置當前runloop的commonMode模式時可以防止scrollView頁面滑動Timer的停滯

• scheduledTimer block

timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true,               block: { (timer) in
       print(timer)
 })

這種操作默認把timer加入到當前runloop的default模式下
2.GCD方式的Timer

var gcdTimer: DispatchSourceTimer?
...
gcdTimer = DispatchSource.makeTimerSource()
gcdTimer?.schedule(deadline: DispatchTime.now(), repeating: DispatchTimeInterval.seconds(1))
gcdTimer?.setEventHandler(handler: {
            print("走你GCD")
    })
gcdTimer?.resume()

不受線程runloop的影響。它會在自己所在的線程中一直執行下去，直到被suspend或者cancel
3.CADisplayLink方式的Timer

 var cadTimer: CADisplayLink?
...
cadTimer = CADisplayLink(target: self, selector: #selector(timerFire))
cadTimer?.preferredFramesPerSecond = 1
cadTimer?.add(to: RunLoop.current, forMode: .common)

4.RxSwift的Timer

 var timer: Observable<Int>!
...
timer = Observable<Int>.interval(RxTimeInterval.seconds(1), scheduler: MainScheduler.instance)
        timer.subscribe(onNext: { (num) in
            print(num)
        })
        .disposed(by: disposeBag)

不受線程runloop的影響

RxSwift的Timer源碼分析

由interval源碼我們首先來到

public static func interval(_ period: RxTimeInterval, scheduler: SchedulerType)
        -> Observable<Element> {
        return Timer(
            dueTime: period,
            period: period,
            scheduler: scheduler
        )
    }

period是TimeInterval類型,表示執行每一次的時間周期
scheduler是調度者
來到Timer源碼

final private class Timer<Element: RxAbstractInteger>: Producer<Element> {
    fileprivate let _scheduler: SchedulerType
    fileprivate let _dueTime: RxTimeInterval
    fileprivate let _period: RxTimeInterval?

    init(dueTime: RxTimeInterval, period: RxTimeInterval?, scheduler: SchedulerType) {
        self._scheduler = scheduler
        self._dueTime = dueTime
        self._period = period
    }

    override func run<Observer: ObserverType>(_ observer: Observer, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where Observer.Element == Element {
        if self._period != nil {
            let sink = TimerSink(parent: self, observer: observer, cancel: cancel)
            let subscription = sink.run()
            return (sink: sink, subscription: subscription)
        }
        else {
            let sink = TimerOneOffSink(parent: self, observer: observer, cancel: cancel)
            let subscription = sink.run()
            return (sink: sink, subscription: subscription)
        }
    }
}

Timer初始化中保存_scheduler,_dueTime,_period,并重寫了run方法,內部使用TimerSink調用run方法