Swift - UIButton Checkbox in UITableViewCell subclass - NSUserDefaults

I am implementing a UIButton (checkbox) into a custom prototype UITableViewCell subclass. The functionality of the check/unchecked state works, but for the life of me, even with all the tutorials and questions asked on here, I cannot get the state of the button to save in NSUserDefaults.

My ViewController:

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

var defaults = NSUserDefaults.standardUserDefaults()


override func viewDidLoad() {
    super.viewDidLoad()

    //NSUserDefaults go here

    checked = defaults.boolForKey("boxIsChecked")

    }

My UITableViewCell subclass:

class TableViewCell: UITableViewCell {

let isSelected = UIImage(named: "Selected")
let unselected = UIImage(named: "Unselected")


@IBOutlet weak var checkBoxButton: UIButton!
@IBAction func checkBox(sender: UIButton) {
    var defaults = NSUserDefaults.standardUserDefaults()
    if (!checked) {
        checked = true
        checkBoxButton.setImage(isSelected, forState: UIControlState.Normal)
        defaults.setBool(checked, forKey: "boxIsChecked")
    }

    else if (checked) {
        checked = false
        checkBoxButton.setImage(unselected, forState: UIControlState.Normal)
        defaults.setBool(checked, forKey: "boxIsChecked")
    }

}

func checkTheBox() {
    if (!checked) {
        checkBoxButton.setImage(unselected, forState: UIControlState.Normal)
    }

    else if (checked) {
        checkBoxButton.setImage(isSelected, forState: UIControlState.Normal)
    }
}

}