How to unarchive custom array with NSUserDefaults?

Question

I'm saving an array of type ClassA to NSUserDefaults. ClassA look like this:

class ClassA :NSObject, NSCoding{

    init (descriptionParam: String) {
        self.description = descriptionParam
    }

    var description: String?

    required init(coder aDecoder: NSCoder) {
        if let description = aDecoder.decodeObjectForKey("description") as? String {
            self.description = description
        }
    }

    func encodeWithCoder(aCoder: NSCoder) {
        if let description = self.description {
            aCoder.encodeObject(description, forKey: "description")
        }
    }

}

This is how I'm saving the array to NSUserDefaults:

let myData = NSKeyedArchiver.archivedDataWithRootObject(ClassAManager.classa_array)
userDefaults.setObject(myData, forKey: "classAarray");

I'm doing the following in my initial viewDidLoad():

var classA: AnyObject? = NSUserDefaultsManager.userDefaults.objectForKey("classAarray") as AnyObject?
let classAunpacked = NSKeyedUnarchiver.unarchiveObjectWithData(classA) as [ClassA]

I get the following compile-time error on the second line above (the one with let):

Cannot invoke 'unarchiveObjectWithData' with an argument list of type '(AnyObject?)'

However, if I try to retrieve the array with anything other than AnyObject?, I get other compile time errors. It also seems I can't cast from AnyObject? to [ClassA]. Any ideas how this should be done?

Answer 1

unarchiveObjectWithData takes an NSData as it's sole argument, not an optional AnyObject. Since the result of unarchive... is also an optional, I'd suggest using:

if let classA = NSUserDefaultsManager.userDefaults.dataForKey("classAarray") {
    if let classAunpacked = NSKeyedUnarchiver.unarchiveObjectWithData(classA) as? [ClassA] {
        // Use classAunpacked here
    }
}