How to play a sound using Swift?

Most preferably you might want to use AVFoundation. It provides all the essentials for working with audiovisual media.

Update: Compatible with Swift 2, Swift 3 and Swift 4 as suggested by some of you in the comments.

---

Swift 2.3

import AVFoundation

var player: AVAudioPlayer?

func playSound() {
    let url = NSBundle.mainBundle().URLForResource("soundName", withExtension: "mp3")!

    do {
        player = try AVAudioPlayer(contentsOfURL: url)
        guard let player = player else { return }

        player.prepareToPlay()
        player.play()

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

---

Swift 3

import AVFoundation

var player: AVAudioPlayer?

func playSound() {
    guard let url = Bundle.main.url(forResource: "soundName", withExtension: "mp3") else { return }

    do {
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        try AVAudioSession.sharedInstance().setActive(true)

        let player = try AVAudioPlayer(contentsOf: url)

        player.play()

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

---

Swift 4 (iOS 13 compatible)

import AVFoundation

var player: AVAudioPlayer?

func playSound() {
    guard let url = Bundle.main.url(forResource: "soundName", withExtension: "mp3") else { return }

    do {
        try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default)            
        try AVAudioSession.sharedInstance().setActive(true)

        /* The following line is required for the player to work on iOS 11. Change the file type accordingly*/
        player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileType.mp3.rawValue)

        /* iOS 10 and earlier require the following line:
        player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileTypeMPEGLayer3) */

        guard let player = player else { return }

        player.play()

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

Make sure to change the name of your tune as well as the extension. The file needs to be properly imported (Project Build Phases > Copy Bundle Resources). You might want to place it in assets.xcassets for greater convenience.

For short sound files you might want to go for non-compressed audio formats such as .wav since they have the best quality and a low cpu impact. The higher disk-space consumption should not be a big deal for short sound files. The longer the files are, you might want to go for a compressed format such as .mp3 etc. pp. Check the compatible audio formats of CoreAudio.

---

Fun-fact: There are neat little libraries which make playing sounds even easier. :)
For example: SwiftySound

For Swift 3 :

import AVFoundation

/// **must** define instance variable outside, because .play() will deallocate AVAudioPlayer 
/// immediately and you won't hear a thing
var player: AVAudioPlayer?

func playSound() {
    guard let url = Bundle.main.url(forResource: "soundName", withExtension: "mp3") else {
        print("url not found")
        return
    }

    do {
        /// this codes for making this app ready to takeover the device audio
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        try AVAudioSession.sharedInstance().setActive(true)

        /// change fileTypeHint according to the type of your audio file (you can omit this)

        player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileTypeMPEGLayer3)

        // no need for prepareToPlay because prepareToPlay is happen automatically when calling play()
        player!.play()
    } catch let error as NSError {
        print("error: \(error.localizedDescription)")
    }
}

The best practice for local assets is to put it inside assets.xcassets and you load the file like this :

func playSound() {
    guard let url = Bundle.main.url(forResource: "soundName", withExtension: "mp3") else {
        print("url not found")
        return
    }

    do {
        /// this codes for making this app ready to takeover the device audio
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        try AVAudioSession.sharedInstance().setActive(true)

        /// change fileTypeHint according to the type of your audio file (you can omit this)

        /// for iOS 11 onward, use :
        player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileType.mp3.rawValue)

        /// else :
        /// player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileTypeMPEGLayer3)

        // no need for prepareToPlay because prepareToPlay is happen automatically when calling play()
        player!.play()
    } catch let error as NSError {
        print("error: \(error.localizedDescription)")
    }
}