UIScrollView contentOffset error?
I have set the isPagingEnabled
element's scrollView property to true
for example:
let scrollView = UIScrollView(frame: view.bounds)
scrollView.contentSize = CGSize(width: view.bounds.width * 2, height: 0)
scrollView.delegate = self
scrollView.isPagingEnabled = true
view.addSubview(scrollView)
and the delegate method:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
print(scrollView.contentOffset.x)
}
When scrolling the view to the border, the console prints as shown:
and
The values in the red box shouldn't be printed, right?
But, if the setting isPagingEnabled
is false
, console printing is fine. Is this a bug UIScrollView
?
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Your content offset is not displayed correctly because you are using the content size in the viewdidload using the content size in this method than printing your content with the set
override func viewDidLayoutSubviews()
{
scrollView.contentSize = CGSize(width: view.bounds.width * 2, height: 0)
}
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As far as I know, it works correctly when you set the contentSize on the scrollview , which will respond to their delegate the first time around itself.
func scrollViewDidScroll (_ scrollView: UIScrollView)
Whenever the user tries to scroll or drag, the above delegate will be called recursively. Here your contentSize width is twice the width of your view borders (so there are two pages, contentOffset.x will start at 0 and the current scroll position, if it's on the second page, this will give you a view width * n ) and you set isPagingEnabled to true strong>.
Check out https://developer.apple.com/reference/uikit/uiscrollview/1619404-contentoffset
The default is CGPoint Zero .
In fact contentOffset will tell you what the current scroll position is.
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Whenever it UIScrollView
scrolls, this method scrollViewDidScroll(_ scrollView: UIScrollView)
calls. Any direction if you scroll down will get these types of output.
However, if you want to use subcategorization, then instead of this method you can use:
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
let pageNumber = round(scrollView.contentOffset.x / scrollView.frame.size.width)
print("pageNumber = \(pageNumber)")
}
With this method, you will get the exact page no UIScrollView
.
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Please use a frame instead of borders.
The bounds of a UIView is a rectangle expressed as a location (x, y) and size (width, height) relative to its own coordinate system (0,0). The frame of a UIView is a rectangle, expressed as a location (x, y) and size (width, height) relative to the overlap it is contained in.
let scrollView = UIScrollView(frame: view.frame.size)
scrollView.contentSize = CGSize(width: view.frame.size.width * 2,
height: 0)
scrollView.delegate = self
scrollView.isPagingEnabled = true
view.addSubview(scrollView)