ios - UIScrollView 在滚动时对齐位置

Question

我正在尝试实现在滚动时捕捉到点的滚动视图。

我在这里看到的所有帖子都是关于“在”用户结束拖动滚动后捕捉到一个点。我想让它在拖动过程中捕捉。

到目前为止，我有这个来阻止拖动后的惯性，它工作正常：

func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
      targetContentOffset.memory = scrollView.contentOffset
}

我试过了，但没有按预期工作：

    var scrollSnapHeight : CGFloat = myScrollView.contentSize.height/10

scrollViewDidScroll：

func scrollViewDidScroll(scrollView: UIScrollView) {
    let remainder : CGFloat = scrollView.contentOffset.y % scrollSnapHeight
    var scrollPoint : CGPoint = scrollView.contentOffset
    if remainder != 0 && scrollView.dragging
    {
        if self.lastOffset > scrollView.contentOffset.y //Scrolling Down
        {
            scrollPoint.y += (scrollSnapHeight - remainder)
            NSLog("scrollDown")
        }
        else //Scrolling Up
        {
            scrollPoint.y -= (scrollSnapHeight - remainder)
        }
        scrollView .setContentOffset(scrollPoint, animated: true)
    }
    self.lastOffset = scrollView.contentOffset.y;
}

Answer 1

这种方法将启用/禁用scrollEnabled.UIScrollView

当 scrollView 滚动到给定之外时，scrollSnapHeight使到. 这将停止滚动。然后再次启用滚动以进行下一次拖动。scrollEnabledfalse

extension ViewController: UIScrollViewDelegate {

    func scrollViewDidScroll(scrollView: UIScrollView) {

        if scrollView.contentOffset.y > lastOffset + scrollSnapHeight {
            scrollView.scrollEnabled = false
        } else if scrollView.contentOffset.y < lastOffset - scrollSnapHeight {
            scrollView.scrollEnabled = false
        }
    }

    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {

        guard !decelerate else {
            return
        }

        setContentOffset(scrollView)
    }

    func scrollViewWillBeginDecelerating(scrollView: UIScrollView) {

        setContentOffset(scrollView)
    }
}

---

func setContentOffset(scrollView: UIScrollView) {

    let stopOver = scrollSnapHeight
    var y = round(scrollView.contentOffset.y / stopOver) * stopOver
    y = max(0, min(y, scrollView.contentSize.height - scrollView.frame.height))
    lastOffset = y

    scrollView.setContentOffset(CGPointMake(scrollView.contentOffset.x, y), animated: true)

    scrollView.scrollEnabled = true
}

Answer 2

子类 UIScrollView/UICollectionView

此解决方案不需要您抬起手指即可在滚动时取消捕捉和工作。如果您需要它进行垂直滚动而不是水平滚动，只需将 x 与 y 交换即可。

将snapPoint设置为您希望捕捉中心所在的内容偏移量。

将snapOffset设置为您希望在 snapPoint 周围发生捕捉的半径。

如果您需要知道 scrollView 是否已捕捉，只需检查isSnapped变量。

class UIScrollViewSnapping : UIScrollView {
    public var snapPoint: CGPoint?
    public var snapOffset: CGFloat?
    public var isSnapped = false
    
    public override var contentOffset: CGPoint {
        set {
            if let snapPoint = self.snapPoint,
                let snapOffset = self.snapOffset,
                newValue.x > snapPoint.x - snapOffset,
                newValue.x < snapPoint.x + snapOffset {
                self.isSnapped = true
                super.contentOffset = snapPoint
            }
            else {
                self.isSnapped = false
                super.contentOffset = newValue
            }
        }
        get {
            return super.contentOffset
        }
    }
}