I need a reliable StopWatch in Swift 3 - swift

Question

I need a reliable StopWatch in Swift 3. I came up with this based on another example found on SO ...
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")
}
}
But this doesn't seem to work reliably. Fetching seconds are often staying at 0 or in other cases when accessing seconds they don't start from 0. What is wrong with this code?

Answer 1

It's most likely a threading issue. If UI is involved you have to make sure that the UI related code runs on the main thread.
The variable started is redundant. Checking the timer for nil does the same.
This code adds a DispatchQueue.main block. Put your code to update the UI into this 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")
}
}