IOS SWIFT 투명 네비게이션바 만들기, clear color navigationbar (UINavigationController)

import UIKit
 
 
class DetailViewController: UIViewController {
 
    override func viewDidLoad() {
        super.viewDidLoad()
        self.setNavigationBar() //네비바 셋팅
        // Do any additional setup after loading the view.
    }
 
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    func setNavigationBar(){
        let bar:UINavigationBar! =  self.navigationController?.navigationBar
        bar.setBackgroundImage(UIImage(), forBarMetrics: UIBarMetrics.Default)
        bar.shadowImage = UIImage()
        bar.backgroundColor = UIColor.clearColor()
    }
 
}