修改UINavigationBar 类

 var item:UINavigationItem = UINavigationItem();

        var viewTitle = UIView();

            viewTitle.backgroundColor = UIColor.redColor();

            viewTitle.frame = CGRectMake(0, 0, 20, 30)

        item.titleView = viewTitle;

        var button:UIBarButtonItem = UIBarButtonItem(title: "Left_1", style: UIBarButtonItemStyle.Done, target: nil, action: "aaa");

         var button2:UIBarButtonItem = UIBarButtonItem(title: "Left_2", style: UIBarButtonItemStyle.Done, target: nil, action: "aaa");

        var button3:UIBarButtonItem = UIBarButtonItem(title: "Right_1", style: UIBarButtonItemStyle.Done, target: nil, action: "aaa");

        var button4:UIBarButtonItem = UIBarButtonItem(title: "Right_2", style: UIBarButtonItemStyle.Done, target: nil, action: "aaa");

        item.leftBarButtonItems = [button,button2]

        item.rightBarButtonItems = [button3,button4]

        nav.pushNavigationItem(item, animated: true);