A repeating GCD timer that can run on a background queue

RepeatingTimer.swift

/// RepeatingTimer mimics the API of DispatchSourceTimer but in a way that prevents
/// crashes that occur from calling resume multiple times on a timer that is
/// already resumed (noted by https://github.com/SiftScience/sift-ios/issues/52
class RepeatingTimer {

    let timeInterval: TimeInterval
    
    init(timeInterval: TimeInterval) {
        self.timeInterval = timeInterval
    }
    
    private lazy var timer: DispatchSourceTimer = {
        let t = DispatchSource.makeTimerSource()
        t.schedule(deadline: .now() + self.timeInterval, repeating: self.timeInterval)
        t.setEventHandler(handler: { [weak self] in
            self?.eventHandler?()
        })
        return t
    }()

    var eventHandler: (() -> Void)?

    private enum State {
        case suspended
        case resumed
    }

    private var state: State = .suspended

    deinit {
        timer.setEventHandler {}
        timer.cancel()
        /*
         If the timer is suspended, calling cancel without resuming
         triggers a crash. This is documented here https://forums.developer.apple.com/thread/15902
         */
        resume()
        eventHandler = nil
    }

    func resume() {
        if state == .resumed {
            return
        }
        state = .resumed
        timer.resume()
    }

    func suspend() {
        if state == .suspended {
            return
        }
        state = .suspended
        timer.suspend()
    }
}

This is not working when app goes in background. Any idea on resolution? Please help.

This is not working when app goes in background. Any idea on resolution? Please help.

As far as I know, timers do not work in the background. What do you user your timer for?

If you have a stopwatch type of UI where your time needs to update when user reopens the app, try saving a timestamp when the app is backgrounded. Then, when app is foregrounded again by the user, calculate the diff in time and update your UI and restart your timer.

@iSachdeva & @Streebor, any solution for run a background timer?