滚动时将UIScrollView对齐到位置 [英] UIScrollView snap-to-position while scrolling

问题描述

我正在尝试实现一个滚动视图，该视图在滚动时会捕捉到点.

I am trying to implement a scroll view that snaps to points while scrolling.

我在这里看到的所有帖子都涉及到用户结束拖动滚动后捕捉"到某个点.我想在拖动过程中使它对齐.

All the posts here I've seen about snapping to a point 'after' the user has ended dragging the scroll. I want to make it snap during dragging.

到目前为止，我已经可以在拖动后停止惯性了，并且效果很好:

So far I have this to stop the inertia after dragging and it works fine:

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

我尝试了此操作，但没有按要求工作:

I tried this but not working as desired:

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

scrollViewDidScroll:

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;
}

推荐答案

此方法将启用/禁用UIScrollView的scrollEnabled属性.

This approach is going to enable / disable scrollEnabled property of UIScrollView.

scrollView滚动到给定的scrollSnapHeight之外时，将scrollEnabled设置为false.那将停止滚动.然后再次启用滚动功能以进行下一次拖动.

When scrollView scrolls outside the given scrollSnapHeight, make scrollEnabled to false. That will stop the scrolling. Then make scrolling enable again for the next drag.

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
}

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