Ios 滚动视图分页

我想创建幻灯片来解锁动画，就像它出现在iPhone锁屏上一样。我希望用户向右滑动，以便另一个视图出现在前面。我该怎么做？我已经试过了，下面是我的代码：-

import UIKit

class PageViewController: UIViewController, UIScrollViewDelegate {

@IBOutlet weak var scrollView: UIScrollView!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.

    setUpScrollView()
}

func setUpScrollView () {

    let storyboard = UIStoryboard(name: "Main", bundle: nil)

    let aViewController = storyboard.instantiateViewControllerWithIdentifier("Hello") as! HelloViewController;
    let bViewController = storyboard.instantiateViewControllerWithIdentifier("Home") as! HomeViewController;

    let viewControllers = [bViewController, aViewController]

    scrollView.pagingEnabled = true
    scrollView.contentSize.height = 600

    var contentSizeWidth = CGFloat(2) * self.view.frame.width
    scrollView.contentSize.width =  contentSizeWidth
    scrollView.showsHorizontalScrollIndicator = false
    scrollView.showsVerticalScrollIndicator = false
    scrollView.scrollsToTop = false
    scrollView.delegate = self

    // add all views to scrollView
    for (index, vc) in enumerate(viewControllers) {
        var frame = self.view.frame
        frame.origin.x = frame.width * CGFloat(index)
        frame.origin.y = 0
        vc.view.frame = frame

        self.addChildViewController(vc)
        self.scrollView.addSubview(vc.view)
        vc.didMoveToParentViewController(self)
    }
       }

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

}

我面临的问题是，左边的视图被裁剪了。为了让您直观地看到这一点，当iOS模拟器启动时，会出现带有幻灯片解锁标签的视图。但是当我向右滑动时，scrollView工作得很好，只截取了第二个视图（它在最左边，占据的屏幕不到理想情况下完全占据的一半。请在这里帮助我。提前感谢