https://stackoverflow.com/questions/63043081/nstableview-selected-row-flickering-while-scrolling-with-arrow-keys

ViewController.swift

class ClipView: NSClipView {
    var isScrollAnimationEnabled: Bool = true
    
    override func scroll(to newOrigin: NSPoint) {
        if isScrollAnimationEnabled {
            super.scroll(to: newOrigin)
        } else {
            setBoundsOrigin(newOrigin)
        }
    }
}

class OutlineView: NSOutlineView {
    private var arrowKeysDown = Set<UInt16>()
    
    override func keyDown(with event: NSEvent) {
        if (125...126).contains(event.keyCode) {
            arrowKeysDown.insert(event.keyCode)
            (enclosingScrollView?.contentView as? ClipView)?.isScrollAnimationEnabled = false
        }
        super.keyDown(with: event)
    }
    
    override func keyUp(with event: NSEvent) {
        super.keyUp(with: event)
        arrowKeysDown.remove(event.keyCode)
        (enclosingScrollView?.contentView as? ClipView)?.isScrollAnimationEnabled = arrowKeysDown.isEmpty
    }
}

@tesch

First - You'd like to disable/enable scrolling only when Up / Down arrow keys are pressed / released.
Second - imagine this:

1. Up arrow key down (scrolling explicitly disabled)
2. Down arrow key down (scrolling explicitly disabled)
3. Up arrow key up (scrolling explicitly enabled, but the Down arrow key is still down)

Sometimes, especially on non full sized keyboards, I press both Up & Down arrow keys down, realize this, move my finger a bit and one key is released then (up), but another one is still down. In this case, you do not want to enable scrolling again until you release both of them, because the table/outline view is still scrolling.

It's an edge case, but can happen.

Did update the gist. We can set it to false explicitly in the keyDown, but we have to keep it in the keyUp to be sure that both Up / Down arrow keys are released.

@zrzka

I see, thanks. In practice I wasn't able to re-enable the scrolling animation with the scenario you described, as the down arrow keeps calling key down, which immediately disables it again. But it sure is best practice to not rely on that.

Yeah, you're probably right, feel free to modify it in any way :)