swift - 我需要一个可靠的 Swift 3 秒表

Question

我需要 Swift 3 中可靠的 StopWatch。我根据在 SO 上找到的另一个示例想出了这个 ...

import Foundation

class StopWatch {
    public private(set) var seconds:Double = 0
    public var milliseconds: Double { return seconds * 1000 }     
    private weak var timer:Timer?
    private var startTime:Double = 0
    public private(set) var started = false       
    public func start() {
        if started { return }
        started = true
        startTime = Date().timeIntervalSinceReferenceDate
        timer = Timer.scheduledTimer(withTimeInterval: 0.05, repeats: true) {
            timer in
            if !self.started { return }
            self.seconds = Date().timeIntervalSinceReferenceDate - self.startTime
            print("Seconds: \(self.seconds)")
        }
        print("Started")
    }

    public func stop() {
        if !started { return }
        timer?.invalidate()
        started = false
        print("Stopped")
    }
}

但这似乎并不可靠。获取秒数通常保持在 0，或者在其他情况下，当访问秒数时它们不是从 0 开始。这段代码有什么问题？

Answer 1

这很可能是线程问题。如果涉及 UI，则必须确保与 UI 相关的代码在主线程上运行。

变量started 是多余的。检查计时器是否为 nil 也是如此。

此代码添加了一个 DispatchQueue.main block 。将您用于更新 UI 的代码放入此 block

class StopWatch {
    public private(set) var seconds:Double = 0
    public var milliseconds: Double { return seconds * 1000 }
    private weak var timer : Timer?
    private var startTime : Double = 0
    private var timerIsRunning : Bool { return timer != nil }

    public func start() {
        if timerIsRunning { return }
        startTime = Date().timeIntervalSinceReferenceDate
        timer = Timer.scheduledTimer(withTimeInterval: 0.05, repeats: true) { timer in
            self.seconds = Date().timeIntervalSinceReferenceDate - self.startTime
            print("Seconds: \(self.seconds)")
            DispatchQueue.main.async {
                // do something on the main thread
            }
        }
        print("Started")
    }

    public func stop() {
        if !timerIsRunning { return }
        timer!.invalidate()
        timer = nil
        print("Stopped")
    }
}