How to use NSScroller in a custom NSView
<p>I have a custom NSView with two NSClipViews. I want to add a vertical scroller for each clipview. The snippet below shows a NSScroller, but it is not drawing any knob or buttons. Interaction is also not possible.
NSScroller is a small class, so I am not sure what I am missing here.</p>

<pre><code>required init?(coder: NSCoder)
{
    super.init(coder: coder)

    let width = NSScroller.scrollerWidthForControlSize(NSControlSize.RegularControlSize, scrollerStyle: NSScrollerStyle.Overlay)

    let scroller = NSScroller(frame: NSRect(x: 10, y: 10, width: width, height: 500))
    self.addSubview(scroller)
    scroller.doubleValue = 0.5
    scroller.knobProportion = 0.1
    scroller.needsLayout = true  //no effect
    scroller.needsDisplay = true //no effect
}
</code></pre>