集合视图中的水平滚动

Question

I wish to do something when my collection view cell is scrolled horizontally. But I do not know which function gets called when it is getting scrolled.

I have a collection view cell inside of a table view cell, and the collection view cell scrolls horizontally

Answer 1

If you use storyboard, in Attributed Inspector you will find an option that Scroll Direction , make it Horizontal , default this is set to Vertical

programitically

let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .vertical
let collectionView = UICollectionView(frame: frame, collectionViewLayout: layout)

Answer 2

1. First, set your collectionview's delegate to your viewcontroller (or view)
2. Implement UIScrollViewDelegate methods inside your viewcontroller and you can track your collectionview's scrolling.

Answer 3

There are several methods that will notify you when a collection view gets scrolled, all of them are contained in UIScrollViewDelegate , and thus in UICollectionViewDelegate protocol, which inherits from the former.

1. scrollViewDidScroll(_:) is indeed called each time the content offset changes . That means not only the active scrolling issued by the user, but also scrolling by inertia, programmatic scrolling and bouncing. You can use this method to react to the scrolling distance, for example, by querying the contentOffset property of the scroll view.
2. scrollViewWillBeginDragging(_:) is, in contrast, getting called only at the beginning of scrolling issued by the user (that's why in the documentation you can see that this method may be called only after some delay, since the scroll view's gesture recognizer needs time to decide if it's a tap or a pan gesture). It will not be called again until the user lifts their finger and starts scrolling again.
3. scrollViewWillBeginDecelerating(_:) is called when the user-issued scrolling discussed above ends, but the scroll view will continue scrolling further to achieve this inertia feeling. Again, it will not get called again until the user lifts their finger one more time.

That's basically it. If this still doesn't narrow down the event that you want to track (for example, you want to become notified when the user starts scrolling at the initial position only), you will need to set some flags or track additional properties.

To track horizontal scrolling for instance, you will need to either compare the scroll view's previous content offset to the current or check the scrolling velocity via scrollView.panGestureRecognizer.velocity(in: collectionView) .