Swift help for a newbie - ios

Question

I am getting the following error message and cannot figure out what I am doing wrong. This is my first program and don't know too much on how to debug it.
Error message:
fatal error: unexpectedly found nil while unwrapping an Optional value
(lldb)
Code:
import UIKit
import AVFoundation
class PlaySoundsViewController: UIViewController {
var audioPlayer:AVAudioPlayer!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
if var filePath = NSBundle.mainBundle().pathForResource("crankringtone", ofType: "mp3"){
var filePathUrl = NSURL.fileURLWithPath(filePath)
audioPlayer = AVAudioPlayer(contentsOfURL: filePathUrl, error: nil)
} else {
println("file path is empty")
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func playSlowAudio(sender: UIButton) {
audioPlayer.stop()
}
}

Answer 1

You need to check if the value of filePathUrl is non-nil before using it.

Answer 2

NSURL.fileURLWithPath(filePath) returns an Optional value which could potentially be nil. You should check before using it:
if let filePath = NSBundle.mainBundle().pathForResource("crankringtone", ofType: "mp3"){
if let filePathUrl = NSURL.fileURLWithPath(filePath) {
audioPlayer = AVAudioPlayer(contentsOfURL: filePathUrl, error: nil)
}
} else {
println("file path is empty")
}

Answer 3

In your code, you've declared the variable audioPlayer var audioPlayer:AVAudioPlayer! The exclamation mark means that it can't be nil when unwrapped.
So, in this code:
if var filePath = NSBundle.mainBundle().pathForResource("crankringtone", ofType: "mp3"){
var filePathUrl = NSURL.fileURLWithPath(filePath)
audioPlayer = AVAudioPlayer(contentsOfURL: filePathUrl, error: nil)
} else {
println("file path is empty")
}
You've got a variable called filePathUrl. That variable is using NSURL.fileURLWithPath(filePath). This can return nil. If it does, then your variable filePathUrl is nil. Then when you use that in audioPlayer, it's nil, so audioPlayer returns nil.
But remember, audioPlayer has a !. It can't be nil. So what you can do (simplest option), is to have an extra if statement:
if let filePath = NSBundle.mainBundle().pathForResource("crankringtone", ofType: "mp3"){
if let filePathUrl = NSURL.fileURLWithPath(filePath) {
audioPlayer = AVAudioPlayer(contentsOfURL: filePathUrl, error: nil)
}
} else {
println("file path is empty")
}
This extra if statement double checks that filePathUrl isn't nil. If it is, it sends the program to the else statement. If it isn't nil, then it allows audioPlayer to do its thing. And, because we know the value isn't nil, audioPlayer won't return an error.

Answer 4

The crash is most likely happening when you tap a button and the playSlowAudio function gets called.
The problem is you are using an implicitly unwrapped optional for audioPlayer. If the initialization of the player failed (for example, file wasn't found), then audioPlayer will be nil. So when the button action is called, audioPlayer.stop() attempt to unwrap audioPlayer before calling stop(), which causes the crash.
To fix, change audioPlayer to be a regular optional:
var audioPlayer:AVAudioPlayer?
And use it with the safer optional chaining:
audioPlayer?.stop()
So the full example will look like this:
import UIKit
import AVFoundation
class PlaySoundsViewController: UIViewController {
var audioPlayer:AVAudioPlayer?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
if var filePath = NSBundle.mainBundle().pathForResource("crankringtone", ofType: "mp3"){
var filePathUrl = NSURL.fileURLWithPath(filePath)
audioPlayer = AVAudioPlayer(contentsOfURL: filePathUrl, error: nil)
} else {
println("file path is empty")
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func playSlowAudio(sender: UIButton) {
audioPlayer?.stop()
}
}