AppDelegate

//1. 创建窗口
        self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
        //2. 显示窗口
        self.window?.makeKeyAndVisible()
        
        let viewCtrl = ViewController()
//        self.window?.rootViewController = viewCtrl
        
        //3. 创建导航控制器，至少需要放入一个页面（第一个页面也叫做根视图控制器）
        let navCtrl = UINavigationController(rootViewController: viewCtrl)
        //文字/图片
        navCtrl.navigationBar.tintColor = UIColor.redColor()
        //整个导航条的颜色
        navCtrl.navigationBar.barTintColor = UIColor.greenColor()
        self.window?.rootViewController = navCtrl

ViewController

        
        self.view.backgroundColor = UIColor.redColor()
        
//        self.title = "第一页"
        //用于设置导航条
//        self.navigationItem.title = "第一页"
        
        //设置导航条中间部分
        let v = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 10))
        v.backgroundColor = UIColor.blueColor()
        self.navigationItem.titleView = v
        
        //设置左侧
//        self.navigationItem.leftBarButtonItem = UIBarButtonItem(title: "左侧", style: .Plain, target: self, action: #selector(leftClicked))
//        self.navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .Bookmarks, target: self, action: #selector(leftClicked))
        
        let originImage = UIImage(named: "1.png")
        //图片总是显示原始颜色
        let image = originImage?.imageWithRenderingMode(.AlwaysOriginal)
        self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: image, style: .Plain, target: self, action: #selector(leftClicked))
        
        let btn = UIButton(type: .System)
        btn.frame = CGRect(x: self.view.frame.size.width / 2 - 75, y: self.view.frame.size.height / 2 - 25, width: 150, height: 50)
        btn.setTitle("下一页", forState: .Normal)
        btn.addTarget(self, action: #selector(didClicked(_:)), forControlEvents: .TouchUpInside)
        self.view.addSubview(btn)

    }
    
    func leftClicked() {
        print("leftClicked")
    }
    
    func didClicked(sender: UIButton) {
        let secondCtrl = SecondViewController()
        
        //每一个“已经”处于导航控制器中的页面，它的navigationController属性不为空
        self.navigationController?.pushViewController(secondCtrl, animated: true)
    }