Swift UIScrollView懒加载的使用

这里是xib拖的控件

 代码：

class ViewController: UIViewController,UIScrollViewDelegate {
    let WIDTH : Double = Double(UIScreen.main.bounds.size.width) //当前的
    @IBOutlet weak var oneBtn: UIButton!
    @IBOutlet weak var twoBtn: UIButton!
    @IBOutlet weak var threeBtn: UIButton!
    @IBOutlet weak var scrollView: UIScrollView!
    
    var vcArr = [UIViewController]()//这里是字ViewController的数组
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        addChildController()
        
     
    }

    @IBAction func oneBtnClick(_ sender: Any) {
        self.oneBtn.isSelected = true;
        self.twoBtn.isSelected = false;
        self.threeBtn.isSelected = false;

        self.scrollView.setContentOffset(CGPoint.init(x: WIDTH*0, y: 0), animated: true)
    }
    @IBAction func twoBtnClick(_ sender: Any) {
        self.oneBtn.isSelected = false;
        self.twoBtn.isSelected = true;
        self.threeBtn.isSelected = false;

        self.scrollView.setContentOffset(CGPoint.init(x: WIDTH*1, y: 0), animated: true)
    }
    @IBAction func threeBtnClick(_ sender: Any) {
        self.oneBtn.isSelected = false;
        self.twoBtn.isSelected = false;
        self.threeBtn.isSelected = true;
        self.scrollView.setContentOffset(CGPoint.init(x: WIDTH*2, y: 0), animated: true)
    }
    
    
    func addChildController(){
        
        for _ in 0...2 {
            let vc:UIViewController = UIViewController.init();
            self.addChild(vc)
            vcArr.append(vc)
        }
      
        
        self.scrollView.contentSize = CGSize.init(WIDTH * 3.0 , height: 0)
        scrollViewDidEndScrollingAnimation(self.scrollView)
    }
    
    /**
        scrollview动画结束调用的方法
    */
    public func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView){
        let width = scrollView.frame.size.width;
        let height = scrollView.frame.size.height;
        let page = Int(scrollView.contentOffset.x/width)
        if(page == 0){
            oneBtnClick(self.oneBtn)
        }else if(page == 1){
            twoBtnClick(self.twoBtn)
        }else if(page == 2){
            threeBtnClick(self.threeBtn)
        }
        let vc = vcArr[page]
        if(vc.isViewLoaded){
            return;
        }
        
        vc.view.frame = CGRect.init(x: width * CGFloat(page), y: 0,  width, height: height)
        self.scrollView.addSubview(vc.view)
        if(page == 0){
            vc.view.backgroundColor = UIColor.red
        }else if(page == 1){
            vc.view.backgroundColor = UIColor.blue
        }else if(page == 2){
            vc.view.backgroundColor = UIColor.gray
        }
    }
    /**
     scrollview手动滑动结束调用的方法
     */
    public func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        scrollViewDidEndScrollingAnimation(self.scrollView)
        let page = Int(scrollView.contentOffset.x/scrollView.frame.size.width)
        if(page == 0){
            oneBtnClick(self.oneBtn)
        }else if(page == 1){
            twoBtnClick(self.twoBtn)
        }else if(page == 2){
            threeBtnClick(self.threeBtn)
        }
    }
        
}