如何实现折叠header？

Question

我试图实现折叠式 UITableView Header，但现在我没有取得任何进展。 This 是我的故事板。我尝试使用 scrollViewDidScroll(scrollView: UIScrollView) 委托方法，但是在容器中嵌入的 table 视图中滚动时，位置根本没有改变。 heightConstraint 是容器 header 视图的高度。 Here 是我的 class 的完整源代码。感谢您的帮助！解决这个问题已经有一段时间了。

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    self.heightConstraint.constant = self.maxHeaderHeight
}

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let absoluteTop: CGFloat = 0
    let absoluteBottom: CGFloat = scrollView.contentSize.height - scrollView.frame.size.height
    let scrollDiff = scrollView.contentOffset.y - self.previousScrollOffset
    let isScrollingDown = scrollDiff > 0 && scrollView.contentOffset.y > absoluteTop
    let isScrollingUp = scrollDiff < 0 && scrollView.contentOffset.y < absoluteBottom

    var newHeight = self.heightConstraint.constant
    if isScrollingDown {
        newHeight = max(self.minHeaderHeight, self.heightConstraint.constant - abs(scrollDiff))
    } else if isScrollingUp {
        newHeight = min(self.maxHeaderHeight, self.heightConstraint.constant + abs(scrollDiff))
    }

    if newHeight != self.heightConstraint.constant {
        self.heightConstraint.constant = newHeight
    }

    self.previousScrollOffset = scrollView.contentOffset.y
}

向上滚动时 header 容器应该 disappear/change 它的位置。

Answer 1

以下是如何处理 headerView height 和 tableView scrolling,

class VC: UIViewController {
    @IBOutlet weak var heightConstraint: NSLayoutConstraint!

    var lastContentOffset: CGFloat = 0.0
    let maxHeaderHeight: CGFloat = 115.0

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) {
            //Scrolled to bottom
            UIView.animate(withDuration: 0.3) {
                self.heightConstraint.constant = 0.0
                self.view.layoutIfNeeded()
            }
        }
        else if (scrollView.contentOffset.y < self.lastContentOffset || scrollView.contentOffset.y <= 0) && (self.heightConstraint.constant != self.maxHeaderHeight)  {
            //Scrolling up, scrolled to top
            UIView.animate(withDuration: 0.3) {
                self.heightConstraint.constant = self.maxHeaderHeight
                self.view.layoutIfNeeded()
            }
        }
        else if (scrollView.contentOffset.y > self.lastContentOffset) && self.heightConstraint.constant != 0.0 {
            //Scrolling down
            UIView.animate(withDuration: 0.3) {
                self.heightConstraint.constant = 0.0
                self.view.layoutIfNeeded()
            }
        }
        self.lastContentOffset = scrollView.contentOffset.y
    }
}

在上面的代码中headerView会，

崩溃当 tableView 是 scrolled up

tableView

scrolled down

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如果您仍然遇到任何问题，请告诉我。

如何实现折叠header？

How to implement a collapsing header?

uiscrollview

uiscrollviewdelegate

ios

swift