如何将外部阴影添加到uitabbar

Question

我在iOS应用中使用UITabBarController。上图显示了应该是什么样子。所以我的问题是如何为uitabbar制作外部阴影？我有一个UITabBarController。到目前为止，这是我的UITabBarController的代码：

import UIKit


class TabBarViewController: UITabBarController, UITabBarControllerDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()

        self.selectedIndex = 3
        self.delegate = self

        UITabBar.appearance().tintColor = UIColor(CGColor: "#6eb18c".CGColor)
        UITabBar.appearance().backgroundImage = UIImage(named:"tabbarBackground.png")


        let selectedBG = UIImage(named:"tabbarBg.png")?.resizableImageWithCapInsets(UIEdgeInsetsMake(0, 0, 0, 0))
        UITabBar.appearance().selectionIndicatorImage = selectedBG

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }



    func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
        if(tabBarController.selectedIndex == 0)
        {
            print("tabbed index 0")
        }
    }


}