`RxSwift`的倒计时计时器

import RxSwift

func countdownTimer(duration: TimeInterval) -> Observable<Int> {
    return Observable.create { observer in
        var remainingTime = Int(duration)
        
        let timer = DispatchSource.makeTimerSource(queue: DispatchQueue.global())
        timer.schedule(deadline: .now(), repeating: .seconds(1))
        timer.setEventHandler {
            if remainingTime > 0 {
                observer.onNext(remainingTime)
                remainingTime -= 1
            } else {
                observer.onCompleted()
            }
        }
        
        timer.resume()
        
        return Disposables.create {
            timer.cancel()
        }
    }
}

// 使用示例
let disposeBag = DisposeBag()

countdownTimer(duration: 10)
    .subscribe(onNext: { remainingTime in
        print("倒计时剩余时间：\(remainingTime)秒")
    }, onCompleted: {
        print("倒计时结束")
    })
    .disposed(by: disposeBag)