Detecting Home Button vs Lock Button in Swift 3

Motivation

Recently, I tried to make a task management app that wants to identify whether my app goes into background due to user switching to another app or pressing the lock button. If he/she locks the screen, the clock goes on. Otherwise, the clock will be interrupted. However, I found out that current solutions to this problem are only applicable to iOS 7 in Objective-C. So I decided to modify it to make it up to date with the new Swift 3 syntax.

Method

It utilizes Darwin Notifications with CFNotificationCallback method to detect lockstatus right after app goes into background. It can be achieved by adding the following code to AppDelegate.swift in four simple steps:

Step 1:

Add the following code right under AppDelegate class declaration

class AppDelegate: UIResponder, UIApplicationDelegate {
    
    var window: UIWindow?

    let displayStatusChanged: CFNotificationCallback = { center, observer, name, object, info in
        let str = name!.rawValue as CFString
        if (str == "com.apple.springboard.lockcomplete" as CFString) {
            let isDisplayStatusLocked = UserDefaults.standard
            isDisplayStatusLocked.set(true, forKey: "isDisplayStatusLocked")
            isDisplayStatusLocked.synchronize()
        }
    }
    
    //other functions
}

Step 2:

Inside didFinishLaunchingWithOptions, add the following code:

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions:
    [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        
        let isDisplayStatusLocked = UserDefaults.standard
        isDisplayStatusLocked.set(false, forKey: "isDisplayStatusLocked")
        isDisplayStatusLocked.synchronize()
        
        // Darwin Notification
        let cfstr = "com.apple.springboard.lockcomplete" as CFString
        let notificationCenter = CFNotificationCenterGetDarwinNotifyCenter()
        let function = displayStatusChanged
        CFNotificationCenterAddObserver(notificationCenter,
                                        nil,
                                        function,
                                        cfstr,
                                        nil,
                                        .deliverImmediately)
        
        return true
    }

Step 3:

Inside applicationDidEnterBackground, add the following code:

func applicationDidEnterBackground(_ application: UIApplication) {      
        let isDisplayStatusLocked = UserDefaults.standard
        if let lock = isDisplayStatusLocked.value(forKey: "isDisplayStatusLocked"){
            // user locked screen
            if(lock as! Bool){            
                // do anything you want here
                print("Lock button pressed.")
            }
            // user pressed home button
            else{            
                // do anything you want here
                print("Home button pressed.")
            }
        }
    }

Step 4:

Inside applicationWillEnterForeground, add the following code:

    func applicationWillEnterForeground(_ application: UIApplication) {
        print("Back to foreground.")
        //restore lock screen setting
        let isDisplayStatusLocked = UserDefaults.standard
        isDisplayStatusLocked.set(false, forKey: "isDisplayStatusLocked")
        isDisplayStatusLocked.synchronize()  
    }

Please download/clone the project for a brief demonstration.

Credit

Detecting Home button vs Lock button - iOS 7 by Jose Santiago