redrawing NSView border during window resize has delay

Question

I made a simple headerView that draws a grey bottom line above the main NSView, like the header in Xcode. Code is shown below:

import Cocoa

class HeaderView: NSView {
    var border = CALayer()

    required init?(coder decoder: NSCoder) {
        super.init(coder: decoder)

        self.wantsLayer = true

        self.layer?.backgroundColor = NSColor.white.cgColor
        border.backgroundColor = NSColor.quaternaryLabelColor.cgColor

        layer?.addSublayer(border)
    }

    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)

        border.frame = CGRect(x: 0.0, y: 0.0, width: frame.width, height: CGFloat(1.0))
    }
}

The line draws, but when I resize the window there is a small delay when the line is redrawn. So if I pull the right side of the window to the right, you can briefly see a gap in the line on the right side.

I also tried adding:

self.layerContentsRedrawPolicy = .duringViewResize

But that did not make a difference.

How can I make sure the line is constantly updated during resizing the window?

Answer 1

I fixed it by using an NSBezierPath:

override func draw(_ dirtyRect: NSRect) {
    super.draw(dirtyRect)

    let path = NSBezierPath()
    path.move(to: NSPoint(x: 0.0, y: 0.0))
    path.line(to: NSPoint(x: frame.width, y: 0.0))
    NSColor.quaternaryLabelColor.setStroke()
    path.stroke()
}