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.

Africa

Answer 1

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]; 

Predecease

Note that his observer is also triggered when the scrolling is performed in code. – Buckra

How do I know if the scroll has ended? – Samekh

Answer 2

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

Stung

Upvoted too soon, it actually does not work as is. CollectionView is not a scroll view. – Gev

apologies, I copy pasted but this is really not the collection but a the scrollview content view – Stung

Answer 3

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.

Harbin

Answer 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)

Gev

Should there also be a subsequent removeObserver call? when the class is deInit ? – Tristantristas

@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" developer.apple.com/documentation/foundation/notificationcenter/… – Gev

thanks, almost like a callback then. You don't have to deregister them either – Tristantristas

Answer 5

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){

    }

Profiteer

Answer 6

Use the following:

NSScrollViewWillStartLiveScrollNotification
NSScrollViewDidLiveScrollNotification
NSScrollViewDidEndLiveScrollNotification

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

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