Getting NSCoding on swift

ClassName.swift

import UIKit

class ClassName: NSObject, NSCoding {
   var myVariable: String?
    
    override init() {}
    
    required init(coder aDecoder: NSCoder) {
        myVariable = aDecoder.decodeObjectForKey("myVariable") as? String
    }
    
    func encodeWithCoder(aCoder: NSCoder) {
        if let theVariable = myVariable {
            aCoder.encodeObject(theVariable, forKey: "myVariable")
        }
    }
    
    func save() {
        let data = NSKeyedArchiver.archivedDataWithRootObject(self)
        NSUserDefaults.standardUserDefaults().setObject(data, forKey: "ClassName")
    }
    
    func clear() {
        NSUserDefaults.standardUserDefaults().removeObjectForKey("ClassName")
    }
    
    class func loadSaved() -> ClassName? {
        if let data = NSUserDefaults.standardUserDefaults().objectForKey("ClassName") as? NSData {
            return NSKeyedUnarchiver.unarchiveObjectWithData(data) as? ClassName
        }
        return nil
    }
}