👀 Views: 108 💬 Answers: 1 📅 Created: 2025-09-01

macos nsoutlineview swift Swift

I'm experiencing an issue with an `NSOutlineView` in my macOS 14 application where the outline view does not expand when the user clicks on a parent item. The data source methods are all implemented, but for some reason, the `outlineView(_:childrenOfItem:)` method isn't returning the expected children in some cases. I've set up my data structure as a nested array, and I can successfully retrieve the children programmatically, but the UI doesn't reflect this. Here’s the relevant part of my implementation: ```swift class MyOutlineViewDataSource: NSObject, NSOutlineViewDataSource { var items: [MyItem] // MyItem has a property children: [MyItem] func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int { guard let parentItem = item as? MyItem else { return items.count } return parentItem.children.count } func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any { let parentItem = item as? MyItem ?? items[index] return parentItem.children[index] } func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool { if let item = item as? MyItem { return !item.children.isEmpty } return true } } ``` I also set the delegate and data source correctly in viewDidLoad: ```swift override func viewDidLoad() { super.viewDidLoad() outlineView.dataSource = dataSource outlineView.delegate = self } ``` Despite this, when clicking on a parent item, no action seems to occur. The `outlineView(_:shouldExpandItem:)` delegate method is not being called at all. I’ve tried reloading the outline view after updating the data source but it still doesn’t work. No errors are thrown, and I’ve verified that the `numberOfChildrenOfItem` method is getting called and returns the correct count. What could be causing the outline view to fail to expand? Is there a specific configuration or a known issue with `NSOutlineView` in macOS 14 that I am overlooking? For context: I'm using Swift on Ubuntu. What's the best practice here?