AppVersion

AppDelegate.swift

class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        AppVersion.activateAndSaveCurrentVersion()
        application.onFirstLaunch {
            showWelcomeMessage()   
        }
        application.onUpgrade { (previousVersion, currentVersion) in
            migrateData(from: previousVersion, to: currentVersion)
        }
        return true
    }
}

AppVersion.swift

class AppVersion {
    
    /*
     Call this function in AppDelegate
     */
    static func activateAndSaveCurrentVersion() {
        // getting these static variables initiliazes them and persists their value to UserDefaults
        let _ = build
        let _ = version
        let _ = full
    }
    
    static let build = AppVersion(infoDictionaryKey: "CFBundleVersion")
    static let version = AppVersion(infoDictionaryKey: "CFBundleShortVersionString")
    static let full = AppVersion(combine: version, with: build)
    
    let previous: String?
    let current: String
    
    private init(infoDictionaryKey: String) {
        let key = "\(AppVersion.self).\(infoDictionaryKey).previous"
        current = Bundle.main.object(forInfoDictionaryKey: infoDictionaryKey) as! String
        previous = UserDefaults.standard.string(forKey: key)
        UserDefaults.standard.set(current, forKey: key)
    }
    
    private init(combine a: AppVersion, with b: AppVersion) {
        if let prevA = a.previous, let prevB = b.previous {
            previous = "\(prevA).\(prevB)"
        } else {
            previous = nil
        }
        current = "\(a.current).\(b.current)"
    }
}

extension UIApplication {
    
    var isFirstLaunch: Bool {
        return AppVersion.full.previous == nil
    }
    var isUpgrade: Bool {
        if let previous = AppVersion.full.previous, previous != AppVersion.full.current {
            return true
        }
        return false
    }
    
    func onFirstLaunch(_ block: @escaping () -> ()) {
        if self.isFirstLaunch {
            block()
        }
    }
    
    func onUpgrade(_ block: @escaping ((previous: String, current: String)) -> ()) {
        if self.isUpgrade {
            block(previous: previous, current: AppVersion.full.current)
        }
    }
}