1.在AppDelegate中判断是否第一次进入，更换根视图

    func application(application: UIApplication,didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
        if(!NSUserDefaults.standardUserDefaults().boolForKey("firstLaunch"))
        {
            NSUserDefaults().setBool(true,forKey: "firstLaunch")
            NSLog("first lanuch")
            var vc : WelcomeController = WelcomeController()
            self.window?.rootViewController = vc
        }
        else{
            NSLog("not first lanuch")
            var navC = ViewController()
            //获取名为Main.storyboard的文件
            var storyboard = UIStoryboard(name: "Main",bundle:nil)
            self.window?.rootViewController = storyboard.instantiateViewControllerWithIdentifier("MainController") as? UINavigationController
        }
        self.window?.backgroundColor = UIColor.whiteColor()
        self.window?.makeKeyAndVisible()
        return true
    }

//页面布局
    func setUI()
    {
        var scrollView = UIScrollView(frame: CGRectMake(0,320,640))
        scrollView.contentSize = CGSizeMake(960,0)
        scrollView.pagingEnabled = true
        var imageView1 = UIImageView(frame: CGRectMake(0,640))
        imageView1.image = UIImage(named: "top_image1")
        scrollView.addSubview(imageView1)
        var imageView2 = UIImageView(frame: CGRectMake(320,640))
        imageView2.image = UIImage(named: "top_image2")
        scrollView.addSubview(imageView2)
        var imageView3 = UIImageView(frame: CGRectMake(640,640))
        imageView3.image = UIImage(named: "top_image3")
        imageView3.userInteractionEnabled = true
        scrollView.addSubview(imageView3)
        var button :UIButton = UIButton()
        button.setTitle("跳转",forState: UIControlState.Normal)
        button.frame = CGRectMake(46,371,230,37)
        //为button添加点击事件
        button.addTarget(self,action: "firstpressed",forControlEvents: UIControlEvents.TouchUpInside)
        imageView3.addSubview(button)
        var page = UIPageControl(frame: CGRectMake(135,600,50,20))
        page.numberOfPages = 3
        scrollView.addSubview(page)
        self.view.addSubview(scrollView)
    }

3.为按钮添加点击事件

    func firstpressed()
    {
        //若在AppDelegate中self.windows.rootviewcontroller = WelcomeController()则
        //        var nav = UIStoryboard(name: "Main",bundle: nil).instantiateViewControllerWithIdentifier("MainController") as? UINavigationController
        
        //若var vc  = storyboard.instantiateViewControllerWithIdentifier("welcomeController") as?  UIViewController
        //       self.window?.rootViewController = vc,则
        
        var nav = self.storyboard?.instantiateViewControllerWithIdentifier("MainController") as? UINavigationController
        self.presentViewController(nav!,animated: false,completion: nil)
    }