How do I save an Int array in Swift using NSUserDefaults?

You should use if let to unwrap your optional value and also a conditional cast. By the way you should also use arrayForKey as follow:

if let loadedArray = UserDefaults.standard.array(forKey: "myArray") as? [Int] {
    print(loadedArray)
}

Or use the nil coalescing operator ??:

let loadedArray = UserDefaults.standard.array(forKey: "myArray") as? [Int] ?? []

Swift 4:

myArray : [Int] = UserDefaults.standard.object(forKey: "myArray") as! [Int]

You want to assign an AnyObject? to an array of Ints, beacuse objectForKey returns AnyObject?, so you should cast it to array this way:

myArray = NSUserDefaults.standardUserDefaults().objectForKey("myArray") as [Int]

If there are no values saved before, it could return nil, so you could check for it with:

if let temp = NSUserDefaults.standardUserDefaults().objectForKey("myArray") as? [Int] {
    myArray = temp
}

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