问题
I am learning how to work with TableViews and I am wondering how can I figure out if the tableView is scrolling up or down ? I been trying various things such as this but it hasn't worked granted that below is for a scrollview and I have a TableView . Any suggestions would be great as I am new at this ...
func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
if scrollView.panGestureRecognizer.translation(in: scrollView).y < 0 {
print("down")
} else {
print("up")
}
}
This is what I have in my tableView code
func tableView(_ tableView:UITableView, numberOfRowsInSection section:Int) -> Int {
return Locations.count
}
func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
if indexPath.row == self.Posts.count - 4 {
reloadTable(latmin: self.latmin,latmax: self.latmax,lonmin: self.lonmin,lonmax: self.lonmax,my_id: myID)
print("Load More")
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "HomePageTVC", for: indexPath) as! NewCell
cell.post.text = Posts[indexPath.row]
cell.fullname.setTitle(FullName[indexPath.row],for: UIControlState.normal)
return cell
}
回答1:
Like @maddy said in the comment of your question, you can check if your UITableView is scrolling by using the UIScrollViewDelegate and further more you could check which direction it scrolls to by using both scrollViewDidScroll and scrollViewWillBeginDragging functions
// 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
} else if (self.lastContentOffset > scrollView.contentOffset.y) {
// did move down
} else {
// didn't move
}
}
Furthermore: You don't need to subclass your UIViewController with UIScrollViewDelegate if you've already subclassed your UIViewController with UITableViewDelegate because UITableViewDelegate is already a subclass of UIScrollViewDelegate
回答2:
You can implement scrollViewWillEndDragging method:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
if targetContentOffset.pointee.y < scrollView.contentOffset.y {
// it's going up
} else {
// it's going down
}
}
回答3:
first we should make two property for last Offset and Current Offset
var lastOffset = CGFloat()
var currentOffset = CGFloat()
then in the Scrollview VC call the scrollViewWillBeginDragging for get current offset
override func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
self.lastOffset = scrollView.contentOffset.y
}
and scrollViewWillBeginDecelerating for get last offset
override func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
self.lastOffset = scrollView.contentOffset.y
viewStatus(scrollView: scrollView)
}
then with this two variable you can know your scrollview W here it goes
let isScrollUp = scrollView.contentOffset.y > self.lastOffset
let isScrollDown = scrollView.contentOffset.y < self.lastOffset
来源：https://stackoverflow.com/questions/43268714/ios-tableview-how-can-i-check-if-it-is-scrolling-up-or-down