Encapsulate iOS background tasks in a Swift class

BackgroundTask.swift

class BackgroundTask {
    private let application: UIApplication
    private var identifier = UIBackgroundTaskInvalid
    
    init(application: UIApplication) {
        self.application = application
    }
    
    class func run(application: UIApplication, handler: (BackgroundTask) -> ()) {
        // NOTE: The handler must call end() when it is done
        
        let backgroundTask = BackgroundTask(application: application)
        backgroundTask.begin()
        handler(backgroundTask)
    }
    
    func begin() {
        self.identifier = application.beginBackgroundTaskWithExpirationHandler {
            self.end()
        }
    }
    
    func end() {
        if (identifier != UIBackgroundTaskInvalid) {
            application.endBackgroundTask(identifier)
        }
        
        identifier = UIBackgroundTaskInvalid
    }
}

func startBackgroundTask() {
    let application = UIApplication.sharedApplication()
    BackgroundTask.run(application) { backgroundTask in
        print("end")
        backgroundTask.end()
    }
    print("begin")
}

prints out in the console:

end
begin

what is the proper behavior/usage of this class?
maybe i don't understanding well..

thanks

This is correct. Please don't confuse it with an async block of code that you would run on a Dispatch background queue. BackgroundTask's job is just to tell UIKit that the code (task) was ran, i.e. the background task finished. Usually you would use this in the application delegate function:

func applicationWillResignActive(application: UIApplication) {
    BackgroundTask.run(application) { backgroundTask in
        print("I'll do something that takes a few seconds")
        // calculate pi to the last digit...
        print("OK, done with the stuff")
        backgroundTask.end()
    }
}

When I try to apply over code in my project but it not work? Can you help me? What should do when I try reconnect socket during Foreground app long time?

If begin is not part of the public API (i.e. the caller who supplies the handler will never call it), it should be private.