如何根据 tableView 的滚动速度控制函数是不是发生

Posted 2023-03-11

【中文标题】如何根据 tableView 的滚动速度控制函数是不是发生

【英文标题】：How do I control the whether a function will happen depending on the speed that a tableView is scrolled如何根据 tableView 的滚动速度控制函数是否发生

【发布时间】：2020-08-25 02:37:57

【问题描述】：

如果用户以任何速度向下滚动，或者如果用户快速向上滚动（或到达视图控制器的顶部），我希望发生一个动作。我正在使用下面的代码来感知任何移动并实现“确实向上移动”和“确实向下移动”cmets 所在的功能，但我想限制向上移动仅在快速滚动或用户到达时发生tableView 的顶部。我该怎么做？

// we set a variable to hold the contentOffSet before scroll view scrolls
var lastContentOffset: CGFloat = 0

// this delegate is called when the scrollView (i.e your UITableView) will start scrolling
func scrollViewWillBeginDragging(_ scrollView: UIScrollView) 
    self.lastContentOffset = scrollView.contentOffset.y


// while scrolling this delegate is being called so you may now check which direction your scrollView is being scrolled to
func scrollViewDidScroll(_ scrollView: UIScrollView) 
    if self.lastContentOffset < scrollView.contentOffset.y 
        // did move up
        // I want this to only occur is the user is scrolling fast
     else if self.lastContentOffset > scrollView.contentOffset.y 
        // did move down
     else 
        // didn't move
    

【参考方案1】：

我想您可以存储调用scrollViewWillBeginDragging 的时间，然后根据scrollViewDidScroll 中的一定时间量测量时间差

var timeScrollingBegan: Date?

func scrollViewWillBeginDragging(_ scrollView: UIScrollView) 
    // ...
    timeScrollingBegan = Date()


func scrollViewDidScroll(_ scrollView: UIScrollView) 
    if self.lastContentOffset < scrollView.contentOffset.y 
        // Calculate time difference in milliseconds
        let timeDifference = Date().timeIntervalSince(timeScrollingBegan) * 1000
        let movementDifference = scrollView.contentOffset.y - lastContentOffset

        // If the movement difference is past a certain threshold
        // in a certain amount of time, then it is too fast. It will
        // take a bit of trial and error to determine the correct threshold
    
    // ...


// You can probably use scrollViewDidEndDecelerating here instead
func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) 
    timeScrollingBegan = nil