Callbacks When an NSScrollView is Scrolled?

Question

I'm making a Mac app which needs to know when the user is scrolling the NSScrollView, however, I can't find any methods like UIScrollView, which has the following delegate methods:

– scrollViewDidScroll:
– scrollViewWillBeginDragging:
– scrollViewDidEndDragging:willDecelerate:
– scrollViewShouldScrollToTop:
– scrollViewDidScrollToTop:
– scrollViewWillBeginDecelerating:
– scrollViewDidEndDecelerating:

Can I have the similar delegate methods for the App Kit? Thanks in advance.

Kai.

score 79 · Accepted Answer · answered Mar 02 '11 at 15:34

79

You can monitor a scroll view's changes by monitoring the bounds of it's content view. First set the content view to post its changes with

[contentView setPostsBoundsChangedNotifications:YES];

Then register as an observer of those notifications with

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(boundsDidChange:) name:NSViewBoundsDidChangeNotification object:contentView];

answered Mar 02 '11 at 15:34

Sean Rich

2,338
2
20
15

Note that his observer is also triggered when the scrolling is performed in code. – Ely Oct 15 '20 at 20:19
1

How do I know if the scroll has ended? – prabhu Mar 18 '22 at 08:22

score 10 · Answer 2 · edited Nov 29 '19 at 14:53

10

Update for Swift 4:

scrollView.contentView.postsBoundsChangedNotifications

Also the call is:

NotificationCenter.default.addObserver(self,
                                       selector: #selector(boundsChange),
                                       name: NSView.boundsDidChangeNotification,
                                       object: scrollView.contentView)

Edit: the collection in mac doesn't inherit from scrollview. updated properly

edited Nov 29 '19 at 14:53

Pavel Alexeev

6,026
4
43
51

answered Mar 22 '18 at 22:14

wolffan

1,084
10
15

Upvoted too soon, it actually does not work as is. `CollectionView` is not a scroll view. – bauerMusic May 06 '18 at 03:31
apologies, I copy pasted but this is really not the collection but a the scrollview content view – wolffan May 07 '18 at 09:18

score 4 · Answer 3 · answered Dec 12 '12 at 08:04

Had the same problem recently... To somewhat emulate deceleration callbacks it is possible to override

-(void) scrollWheel:(NSEvent *)theEvent

of NSScrollView class, but then check theEvent.momentumPhase instead of theEvent.phase for event phases.

score 4 · Answer 4 · answered May 06 '18 at 03:45

4

Adding to @Sean Rich answer.

The contentView is the NSClipView between the NSScrollView and NSCollectionView.

For this to work, both the ClipView needs to be set to postsBoundsChangedNotifications and should be passed in the notification object.

self.clipView.postsBoundsChangedNotifications = true

NotificationCenter.default.addObserver(self,
                                       selector: #selector(collectionViewDidScroll(notification:)),
                                       name: NSView.boundsDidChangeNotification,
                                       object: self.clipView)

answered May 06 '18 at 03:45

bauerMusic

5,470
5
38
53

Should there also be a subsequent removeObserver call? when the class is deInit ? – Sentry.co Nov 02 '20 at 15:02
@eonist Good question. You do not need to remove observer in this call. From Apple: "If your app targets iOS 9.0 and later or macOS 10.11 and later, you do not need to unregister an observer that you created with this function" https://developer.apple.com/documentation/foundation/notificationcenter/1415360-addobserver – bauerMusic Nov 02 '20 at 17:39
thanks, almost like a callback then. You don't have to deregister them either – Sentry.co Nov 03 '20 at 09:53

score 0 · Answer 5 · answered Mar 26 '19 at 10:28

my two cents for swift 4.2 OSX:

....

if let clipView = self.collectionView.superview, let sv = clipView.superview as? NSScrollView{

        let contentView = sv.contentView
        contentView.postsBoundsChangedNotifications = true

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(collectionViewDidScroll(notification:)),
                                               name: NSView.boundsDidChangeNotification,
                                               object: clipView)
}








 //MARK: scrollview observer:

    @objc func collectionViewDidScroll(notification: Notification){

    }

Cal · Answer 6 · 2022-08-25T22:18:15.833

0

Use the following:

NSScrollViewWillStartLiveScrollNotification
NSScrollViewDidLiveScrollNotification
NSScrollViewDidEndLiveScrollNotification

NSNotificationCenter.defaultCenter().addObserver(
    self,
    selector: #selector(scrollViewDidScroll(_:)),
    name: NSScrollViewDidLiveScrollNotification,
    object: scrollView
)

edited Aug 25 '22 at 22:18

answered Aug 25 '22 at 19:02

Cal

359
3
5

Callbacks When an NSScrollView is Scrolled?

6 Answers6

Linked