Swift 3 - How to make timer work in background

Question

i am trying to do an application which can make a timer run in background.

here\'s my code:

let taskManager = Timer.scheduledTimer(timeInterval: 10,          


        

Answer 1

you can go to Capabilities and turn on background mode and active Audio. AirPlay, and picture and picture.

It really works . you don't need to set DispatchQueue . you can use of Timer.

Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (t) in

   print("time")
}

Answer 2

You can achieve this by getting the time-lapse between background and foreground state of the app, here is the code snippet.

import Foundation import UIKit

class CustomTimer {

let timeInterval: TimeInterval
var backgroundTime : Date?
var background_forground_timelaps : Int?


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 {
    NotificationCenter.default.removeObserver(self, name: UIApplication.didEnterBackgroundNotification, object: nil)
    NotificationCenter.default.removeObserver(self, name: UIApplication.willEnterForegroundNotification, object: nil)
    timer.setEventHandler {}
    timer.cancel()
    resume()
    eventHandler = nil
}

func resume() {
    
    NotificationCenter.default.addObserver(self, selector: #selector(didEnterBackgroundNotification), name: UIApplication.didEnterBackgroundNotification, object: nil)
    
    NotificationCenter.default.addObserver(self, selector: #selector(willEnterForegroundNotification), name: UIApplication.willEnterForegroundNotification, object: nil)
    
    if state == .resumed {
        return
    }
    state = .resumed
    timer.resume()
}

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


@objc fileprivate func didEnterBackgroundNotification() {
    self.background_forground_timelaps = nil
    self.backgroundTime = Date()
}

@objc fileprivate func willEnterForegroundNotification() {
    // refresh the label here
    self.background_forground_timelaps = Date().interval(ofComponent: .second, fromDate: self.backgroundTime ?? Date())
    self.backgroundTime = nil
}

}

Use this class like;

self.timer = CustomTimer(timeInterval: 1)
        self.timer?.eventHandler = {
            DispatchQueue.main.sync {
               
                var break_seconds = self.data.total_break_sec ?? 0
                    break_seconds += 1
                    if self.timer?.background_forground_timelaps != nil && self.timer?.backgroundTime == nil{
                        break_seconds += (self.timer?.background_forground_timelaps)!
                        self.timer?.background_forground_timelaps = nil
                    }
                    self.data.total_break_sec = String(break_seconds)
                    self.lblBreakTime.text = PRNHelper.shared.getPlainTimeString(time: TimeInterval(break_seconds))
                
            }
        }
        self.timer?.resume()

This way I am able to get the timer right when resumed the app from background.

Answer 3

A timer can run in the background only if both the following are true:

• Your app for some other reason runs in the background. (Most apps don't; most apps are suspended when they go into the background.) And:

• The timer was running already when the app went into the background.