NSCollectionView Scroll to bottom - macos

Question

I have an NSCollectionView which consists of dozens of rows of single-columned items (chat messages) in a messaging application.
Each item contains a text area of which the heights vary. Therefore the view should be defaulted to the bottom when the view is created and scrolled to the bottom when new messages are received.
I am struggling to either default the scroll to the bottom or work out how to get the height of the CollectionView's contents to scroll to the bottom.
Any help would be greatly appreciated, thanks!

Answer 1

If you support only macOS 10.11 and up, and if you use a NSCollectionViewLayout, you could ask the layouter for the size of the entire content. That's also how the scrollbars are getting sized.
So, in ObjC, you'd simply ask your collectionView for its layouter's content size and scroll to the bottom:
NSSize contentSize = theCollectionView.collectionViewLayout.collectionViewContentSize.height;
[theCollectionView.enclosingScrollView.contentView scrollPoint:NSMakePoint(0, contentSize.height)];

Answer 2

hi i suggest you to work on Offset for horizontal UICollectionView and Apple provided a method for bottom for vertical UICollectionView
UICollectionView Horizontal Next and Previous Item
extension UICollectionView {
func scrollToNextItem() {
let contentOffset = CGFloat(floor(self.contentOffset.x + self.bounds.size.width))
self.moveToFrame(contentOffset: contentOffset)
}
func scrollToPreviousItem() {
let contentOffset = CGFloat(floor(self.contentOffset.x - self.bounds.size.width))
self.moveToFrame(contentOffset: contentOffset)
}
func moveToFrame(contentOffset : CGFloat) {
let frame: CGRect = CGRect(x: contentOffset, y: self.contentOffset.y , width: self.frame.width, height: self.frame.height)
self.scrollRectToVisible(frame, animated: true)
}
}
UICollectionView Vertical Scroll to Bottom
extension UICollectionView {
func scrollToBottom(animated: Bool) {
let sections = self.numberOfSections
if sections > 0 {
let rows = self.numberOfItems(inSection: sections - 1)
let last = IndexPath(row: rows - 1, section: sections - 1)
DispatchQueue.main.async {
self.scrollToItem(at: last, at: .bottom, animated: animated)
}
}
}
}
UITableView Scroll to Bottom
extension UITableView {
func scrollToBottom(animated: Bool) {
let sections = self.numberOfSections
if sections > 0 {
let rows = self.numberOfRows(inSection: sections - 1)
let last = IndexPath(row: rows - 1, section: sections - 1)
DispatchQueue.main.async {
self.scrollToRow(at: last, at: .bottom, animated: animated)
}
}
}
}
Usage
self.collectionView.scrollToBottom(animated: true)
self.tableView.scrollToBottom(animated: true)