Spring load NSOutlineView leaf rows

Question

I've subclassed NSOutlineView and implemented NSSpringLoadingDestination, but springLoadingActivated() is only ever called on non-leaf rows, even though I've implemented springLoadingEntered() and springLoadingUpdated() to indiscriminately return [.enabled]. I assume NSOutlineView's built-in drag & drop support is interfering with my attempts. Is there a workaround for this?

Answer 1

Feels a little hacky, but it seems I can get away with this by spring loading the rows, but also overriding all of the NSDraggingDestination methods to pass the word on to the parent NSOutlineView:

class SpringLoadedOutlineRow: NSTableCellView, NSSpringLoadingDestination {
    var outlineView: NSOutlineView! {
        didSet {
            registerForDraggedTypes(outlineView.registeredDraggedTypes)
        }
    }

    //Pass through `NSDraggingDestination` methods so we don't interfere with `NSOutlineView`
    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        return outlineView.draggingEntered(sender)
    }
    override func prepareForDragOperation(_ sender: NSDraggingInfo) -> Bool {
        return outlineView.prepareForDragOperation(sender)
    }
    override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        return outlineView.performDragOperation(sender)
    }
    override func concludeDragOperation(_ sender: NSDraggingInfo?) {
        outlineView.concludeDragOperation(sender)
    }
    override func draggingExited(_ sender: NSDraggingInfo?) {
        outlineView.draggingExited(sender)
    }

    //Only pass through if we're expandable & not yet expanded (to get `NSOutlineView`'s default disclosure spring-loading); otherwise it will eat our leaf spring-loading
    override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation {
        guard let representedItem = outlineView.item(atRow: outlineView.row(for: self)) else { return outlineView.draggingUpdated(sender) }
        if outlineView.isExpandable(representedItem) && !outlineView.isItemExpanded(representedItem) {
            return outlineView.draggingUpdated(sender)
        } else {
            return []
        }
    }

    //Actually spring-load!
    func springLoadingActivated(_ activated: Bool, draggingInfo: NSDraggingInfo) {
        //Whatever you want
    }

    func springLoadingHighlightChanged(_ draggingInfo: NSDraggingInfo) {

    }

    func springLoadingEntered(_ draggingInfo: NSDraggingInfo) -> NSSpringLoadingOptions {
        return [.enabled]
    }

    func springLoadingUpdated(_ draggingInfo: NSDraggingInfo) -> NSSpringLoadingOptions {
        return [.enabled]
    }
}