在没有更多上下文的情况下，表达类型不明确

Question

class func unarchiveFromFile(file : NSString) -> SKNode? {

    let path = NSBundle.mainBundle().pathForResource(file as String, ofType: "sks")

    var sceneData = NSData.dataWithContentsOfFile(path, options: .DataReadingMappedIfSafe!, error: nil)
    var archiver = NSKeyedUnarchiver(forReadingWithData: sceneData)

    archiver.setClass(self.classForKeyedUnarchiver(), forClassName: "SKScene")
    let scene = archiver.decodeObjectForKey(NSKeyedArchiveRootObjectKey) as GameScene
    archiver.finishDecoding()
    return scene

---

So I'm getting a bug at the var sceneData = NSData saying: type of expression is ambiguous with more context. I'm very stuck

Answer 1

pathForResource returns an optional.
dataWithContentsOfFile expects a non-optional.

Unwrap the optional

let path = NSBundle.mainBundle().pathForResource(file as String, ofType: "sks")!

or do optional binding

if let path = NSBundle.mainBundle().pathForResource(file as String, ofType: "sks") {
 // path is safe
}

Actually the correct syntax of dataWithContentsOfFile is

let sceneData = NSData(contentsOfFile:path, options: .DataReadingMappedIfSafe, error: nil)

and .DataReadingMappedIfSafe never needs to be unwrapped.

EDIT:

The full code:

class func unarchiveFromFile(file : NSString) -> SKNode? {

    if let path = NSBundle.mainBundle().pathForResource(file as String, ofType: "sks") {
        // path is safe
        let sceneData = NSData(contentsOfFile:path, options: .DataReadingMappedIfSafe, error: nil)
        var archiver = NSKeyedUnarchiver(forReadingWithData: sceneData)

        archiver.setClass(self.classForKeyedUnarchiver(), forClassName: "SKScene")
        let scene = archiver.decodeObjectForKey(NSKeyedArchiveRootObjectKey) as GameScene
        archiver.finishDecoding()
        return scene
    }
    return nil
}