Update to Xcode 7.3 and get: unexpectedly found nil while unwrapping an Optional value [duplicate]

问题

The following code works fine with Xcode 7.2.1. After I upgraded to 7.3 I get a crash with: "unexpectedly found nil while unwrapping an Optional value"

var backgroundMusic: SKAudioNode!

func playBackgroundMusic(name: String) {
  var delay = 0.0
  if backgroundMusic != nil {
    backgroundMusic.removeFromParent()
  } else {
delay = 0.1 }
  runAction(SKAction.waitForDuration(delay)) {
    self.backgroundMusic = SKAudioNode(fileNamed: name)
    self.backgroundMusic.autoplayLooped = true
    self.addChild(self.backgroundMusic)
} }

didMoveToView(view: SKView) {
...
playBackgroundMusic("Music.mp3")
}

I also tried cleaning the project, deleting all the Xcode Developer derived data, and verifying that the "Music.mp3" is being built into the main bundle.
Going back to Xcode 7.2.1 and building works fine with the same code.

Been scratching my head on this one most of the day. Is there a better way to do this?

回答1:

Try changing your variable declaration to an optional.

var backgroundMusic: SKAudioNode?

Then unwrap it as so:

if let bm = backgroundMusic {
  bm.removeFromParent()
} else {
  delay = 0.1 }
  runAction(SKAction.waitForDuration(delay)) {
  self.backgroundMusic = SKAudioNode(fileNamed: name)
  self.backgroundMusic.autoplayLooped = true
  self.addChild(self.backgroundMusic)
}

回答2:

try this.With temp constant

var backgroundMusic: SKAudioNode!

func playBackgroundMusic(name: String) {
  var delay = 0.0
  if backgroundMusic != nil {
    backgroundMusic.removeFromParent()
  } else {
  delay = 0.1
  runAction(SKAction.waitForDuration(delay)) {
    let temp = SKAudioNode(fileNamed: name)
    self.backgroundMusic = temp
    self.backgroundMusic.autoplayLooped = true
    self.addChild(self.backgroundMusic)
 } 
}

didMoveToView(view: SKView) {
...
playBackgroundMusic("Music.mp3")
}

来源：https://stackoverflow.com/questions/36273271/update-to-xcode-7-3-and-get-unexpectedly-found-nil-while-unwrapping-an-optional

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