How to automatically go to the next track when the the one is currently playing ends?

I'm quite new to swift and I want to implement a piece of code that helps me to reach the next song when the one is currently playing ends. I tried to copy the code inside my "@IBAction func nextAction" (which works fine):

@IBAction func nextAction(sender: AnyObject) {
    self.nextTrack()
}

func nextTrack() {

        if trackId == 0 || trackId < 4 {
            if shuffle.on {
                trackId = Int(arc4random_uniform(UInt32(library.count)))
            }else {
                trackId += 1
            }

            if let coverImage = library[trackId]["coverImage"]{
                coverImageView.image = UIImage(named: "\(coverImage).jpg")
            }

            songTitleLabel.text = library[trackId]["title"]
            artistLabel.text = library[trackId]["artist"]

            audioPlayer.currentTime = 0
            progressView.progress = 0

            let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

            if let path = path {
                let mp3URL = NSURL(fileURLWithPath: path)

                do {
                    audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                    audioPlayer.play()

                    NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                    progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }
        }

}

And tried to put it inside an if condition like this (inside the viewDidLoad):

if audioPlayer.currentTime >= audioPlayer.duration {
        self.nextTrack()
    }

I don't have any errors but at runtime this method isn't working and the song ends without playing the next one.

To make the situation more clear here's my controller:

import UIKit
import AVFoundation

class PlayerViewController: UIViewController {

@IBOutlet weak var coverImageView: UIImageView!
@IBOutlet weak var progressView: UIProgressView!
@IBOutlet weak var songTitleLabel: UILabel!
@IBOutlet weak var artistLabel: UILabel!
@IBOutlet weak var shuffle: UISwitch!

var trackId: Int = 0
var library = MusicLibrary().library
var audioPlayer: AVAudioPlayer!

override func viewDidLoad() {
    super.viewDidLoad()


    // Do any additional setup after loading the view.
    if let coverImage = library[trackId]["coverImage"]{
    coverImageView.image = UIImage(named: "\(coverImage).jpg")
    }

    songTitleLabel.text = library[trackId]["title"]
    artistLabel.text = library[trackId]["artist"]

    let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

    if let path = path {
        let mp3URL = NSURL(fileURLWithPath: path)

        do {
            audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
            audioPlayer.play()

            NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
            progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

        } catch let error as NSError {
            print(error.localizedDescription)
        }
    }

}

override func viewWillDisappear(animated: Bool) {
    audioPlayer.stop()
}

func updateProgressView(){

    if audioPlayer.playing {

        progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: true)
    }

}


@IBAction func playAction(sender: AnyObject) {
    if !audioPlayer.playing {
        audioPlayer.play()
    }

}

@IBAction func stopAction(sender: AnyObject) {

    audioPlayer.stop()
    audioPlayer.currentTime = 0
    progressView.progress = 0
}


@IBAction func pauseAction(sender: AnyObject) {
audioPlayer.pause()
}

@IBAction func fastForwardAction(sender: AnyObject) {
    var time: NSTimeInterval = audioPlayer.currentTime
    time += 5.0

    if time > audioPlayer.duration {
        stopAction(self)
    }else {
        audioPlayer.currentTime = time
    }

}

@IBAction func rewindAction(sender: AnyObject) {
    var time: NSTimeInterval = audioPlayer.currentTime
    time -= 5.0

    if time < 0 {
        stopAction(self)
    }else {
        audioPlayer.currentTime = time
    }
}

@IBAction func previousAction(sender: AnyObject) {
    if trackId != 0 || trackId > 0 {
        if shuffle.on {
            trackId = Int(arc4random_uniform(UInt32(library.count)))
        }else {
            trackId -= 1
        }

        if let coverImage = library[trackId]["coverImage"]{
            coverImageView.image = UIImage(named: "\(coverImage).jpg")
        }

        songTitleLabel.text = library[trackId]["title"]
        artistLabel.text = library[trackId]["artist"]

        audioPlayer.currentTime = 0
        progressView.progress = 0

        let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

        if let path = path {
            let mp3URL = NSURL(fileURLWithPath: path)

            do {
                audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                audioPlayer.play()

                NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

            } catch let error as NSError {
                print(error.localizedDescription)
            }
        }
    }




}

@IBAction func swipeDownAction(sender: AnyObject) {
    self.close()
}

@IBAction func closeAction(sender: AnyObject) {
    self.close()
}

@IBAction func nextAction(sender: AnyObject) {
    self.nextTrack()
}

func close() {
    self.dismissViewControllerAnimated(true, completion: nil)
}


func nextTrack() {

        if trackId == 0 || trackId < 4 {
            if shuffle.on {
                trackId = Int(arc4random_uniform(UInt32(library.count)))
            }else {
                trackId += 1
            }

            if let coverImage = library[trackId]["coverImage"]{
                coverImageView.image = UIImage(named: "\(coverImage).jpg")
            }

            songTitleLabel.text = library[trackId]["title"]
            artistLabel.text = library[trackId]["artist"]

            audioPlayer.currentTime = 0
            progressView.progress = 0

            let path = NSBundle.mainBundle().pathForResource("\(trackId)", ofType: "mp3")

            if let path = path {
                let mp3URL = NSURL(fileURLWithPath: path)

                do {
                    audioPlayer = try AVAudioPlayer(contentsOfURL: mp3URL)
                    audioPlayer.play()

                    NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: #selector(PlayerViewController.updateProgressView), userInfo: nil, repeats: true)
                    progressView.setProgress(Float(audioPlayer.currentTime/audioPlayer.duration), animated: false)

                } catch let error as NSError {
                    print(error.localizedDescription)
                }
            }
        }

}

}

All the code is written in Xcode 7.3.1

Any help will be much appreciated, thanks in advance.