如何使用UISCrollView滚动到第一个视图的顶部？

Question

我目前有一个UIMageView（顶部图像）位于Uinavigationbar下方的UISCrollView。但是，我想将UIImageView放置在屏幕顶部（底部图像）。有没有办法实施此功能？

到目前为止，我尝试过的是：我添加了一个UisCrollView扩展名（ source ）向下滚动到提供的视图参数，但对我没有用。

extension UIScrollView {

    // Scroll to a specific view so that it's top is at the top our scrollview
    func scrollToView(view:UIView, animated: Bool) {
        if let origin = view.superview {
            // Get the Y position of your child view
            let childStartPoint = origin.convert(view.frame.origin, to: self)
            // Scroll to a rectangle starting at the Y of your subview, with a height of the scrollview
            self.scrollRectToVisible(CGRect(x:0, y:childStartPoint.y,width: 1,height: self.frame.height), animated: animated)
        }
    }

    // Bonus: Scroll to top
    func scrollToTop(animated: Bool) {
        let topOffset = CGPoint(x: 0, y: -contentInset.top)
        setContentOffset(topOffset, animated: animated)
    }

    // Bonus: Scroll to bottom
    func scrollToBottom() {
        let bottomOffset = CGPoint(x: 0, y: contentSize.height - bounds.size.height + contentInset.bottom)
        if(bottomOffset.y > 0) {
            setContentOffset(bottomOffset, animated: true)
        }
    }

}

class MealDetailsVC: UIViewController {
    private var mealInfo: MealInfo
    
    init(mealInfo: MealInfo) {
        self.mealInfo = mealInfo
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupViews()
        scrollView.scrollToView(view: iv, animated: false)  // used extension from above
    }
    
    lazy var scrollView: UIScrollView = {
        let scrollView = UIScrollView()
        
        return scrollView
    }()
    
    lazy var iv: UIImageView = {
        let iv = UIImageView()
        iv.image = Image.defaultMealImage!   
        iv.contentMode = .scaleAspectFill
        
        return iv
    }()
}

extension MealDetailsVC {
    func setupViews() {
        addBackButton()
        addSubviews()
        autoLayoutViews()
        constrainSubviews()
    }

    fileprivate func addBackButton() {
        ...
    }
    
    @objc func goBack(sender: UIBarButtonItem) {
        ...
    }

    fileprivate func addSubviews() {
        view.addSubview(scrollView)
        scrollView.addSubview(iv)
    }
    
    fileprivate func autoLayoutViews() {
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        iv.translatesAutoresizingMaskIntoConstraints = false
    }

    fileprivate func constrainSubviews() {
        NSLayoutConstraint.activate([
            scrollView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            scrollView.widthAnchor.constraint(equalTo: view.widthAnchor),
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
        
        NSLayoutConstraint.activate([
            iv.topAnchor.constraint(equalTo: scrollView.topAnchor),
            iv.widthAnchor.constraint(equalTo: scrollView.widthAnchor),
            iv.heightAnchor.constraint(equalTo: iv.widthAnchor, multiplier: 0.6)
        ])
    }
}

Answer 1

这可能会有所帮助。

ScrollView.ContentInsetAdjustmentBehavior = .Never

---

有关更多信息，

此属性指定如何使用安全区域插图来修改滚动视图的内容区域。此属性的默认值是UISCROLLVIEWCONTINSETINSETADJUSTMENTAIMATION。

Answer 2

不要设置高度锚点，并添加ImageView CenterXanchor等于ScrollView CenterXanchor约束。将ImageView.ContentMode设置为.scaleaspectFit