Attempts at rendering a view's layer with light/dark interface style

ViewController.swift

//
//  ViewController.swift
//  Rendering
//
//  Created by Kyle Bashour on 11/11/19.
//  Copyright © 2019 Kyle Bashour. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    private let imageView = UIImageView()
    private let renderedView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        imageView.backgroundColor = .systemBlue
        imageView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        imageView.frame = view.bounds
        view.addSubview(imageView)

        // Use dynamic color when setting up the rendered view
        renderedView.backgroundColor = .systemBackground

        renderImage()
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        if traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
            renderImage()
        }
    }

    private func renderImage() {
        renderedView.frame = view.bounds

        let format = UIGraphicsImageRendererFormat(for: traitCollection)
        let renderer = UIGraphicsImageRenderer(bounds: renderedView.bounds, format: format)

        imageView.image = renderer.image { context in
            self.renderedView.layer.render(in: context.cgContext)
        }
    }

    // Setting overrideUserInterfaceStyle before rendering doesn't seem to work
    private func renderImageWithOverride() {
        renderedView.overrideUserInterfaceStyle = traitCollection.userInterfaceStyle

        renderImage()
    }

    // Setting overrideUserInterfaceStyle and redrawing the layer doesn't work
    private func renderImageWithOverrideAndDisplay() {
        renderedView.overrideUserInterfaceStyle = traitCollection.userInterfaceStyle
        renderedView.layer.setNeedsDisplay()
        renderedView.layer.displayIfNeeded()

        renderImage()
    }

}

Stepped on the same problem. I found that overrideUserInterfaceStyle works for the UIView only if it is a subview of some UIWindow.

So this helps before calling renderer:

let window = UIWindow()
window.addSubview(renderedView)

thanks a lot for this comment @pilot34