Dark mode color without xcassets

README.md

Auto updateColor

Like setting color in the XCASSETS, but with code and applyable < iOS 12. By Encapsulating the iOS versioning in the AutoUpdateColor, we can have the UIView.color = ... without the color setup.

// ViewController.swift

let themeMainColor = AutoUpdateColor(lightColor: .blue, darkColor: .yellow)

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = themeMainColor
    }
}

AutoUpdateColor.swift

import UIKit
class AutoUpdateColor: UIColor {
    convenience init(lightColor: UIColor, darkColor: UIColor) {
        if #available(iOS 13.0, *) {
            self.init {
                traitCollection in
                traitCollection.userInterfaceStyle == .dark
                    ? darkColor 
                    : lightColor
            }
        } else {
            self.init(cgColor: lightColor.cgColor)
        }
    }
}

The closure feed to UIColor.init can have more conditions on ENV, such as different theme.