在导航控制器中更改图像y位置

Question

 func addNavBarImage(){
        let navController = navigationController!
        navController.navigationBar.tintColor = UIColor.white
        let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 150, height: 40))
        imageView.contentMode = .scaleAspectFit
        let image = UIImage(named: "toolbar")
        imageView.image = image
        navigationItem.titleView = imageView

    }

  

需要在不触摸导航控制器底部的情况下带来图像   如何将其与导航控制器底部保持至少距离