Swift-Let the tab bar button uitabbaritem the picture centered (no text) _ Use

For the tab bar (Uitabbar), when the Tabbaritem does not need title as long as the image, the image below will occupy a space.
We can set the offset by tabbaritem.imageinsets so that the image icon is centered.

(Note: Top and bottom are set to the opposite number, otherwise the image size will change.) ）

Import UIKit
 
Class MainTabViewController:UITabBarController
{
     Override func viewDidLoad()
     {
         super.viewDidLoad()
         //A total of two views are included
         Let qqView = QQViewController()
         //qqView.title = ""
         Let skypeView = SkypeViewController()
         //skypeView.title = ""
         
         / / Declare two view controllers separately
         Let qq = UINavigationController(rootViewController:qqView)
         qq.tabBarItem.image = UIImage(named:"qq")
         qq.tabBarItem.imageInsets = UIEdgeInsetsMake(6, 0, -6, 0);
         
         Let skype = UINavigationController(rootViewController:skypeView)
         skype.tabBarItem.image = UIImage(named:"skype")
         skype.tabBarItem.imageInsets = UIEdgeInsetsMake(6, 0, -6, 0);
         
         self.viewControllers = [qq, skype]
     }
}