UIScrollview animation depending on content offset

Question

I\'m using a horizontal UIScrollView, and I want a background color transition depending on the x value of the content offset.

Example: The width o

Answer 1

Inspired by @Fogmeister's answer I put the pieces together in swift.

extension UIColor {
    static func color(between start: UIColor, and end: UIColor, percentage: CGFloat) -> UIColor {
        let startRGB = start.rgba
        let stopRGB = end.rgba

        let red: CGFloat = (stopRGB.red - startRGB.red) * percentage + startRGB.red
        let green: CGFloat = (stopRGB.green - startRGB.green) * percentage + startRGB.green
        let blue: CGFloat = (stopRGB.blue - startRGB.blue) * percentage + startRGB.blue
        let alpha: CGFloat = (stopRGB.alpha - startRGB.alpha) * percentage + startRGB.alpha

        return UIColor(red: red, green: green, blue: blue, alpha: alpha)
    }

    var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
        var red: CGFloat = 0
        var green: CGFloat = 0
        var blue: CGFloat = 0
        var alpha: CGFloat = 0
        getRed(&red, green: &green, blue: &blue, alpha: &alpha)
        return (red, green, blue, alpha)
    }
}

Now you can do something like this:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let offset = scrollView.contentOffset.y
    let scrolledDistance = offset + scrollView.contentInset.top
    let progress = max(0, min(1, scrolledDistance / scrollView.contentSize.height))

    someLabel.textColor = .color(between: .red, and: .green, percentage: progress)
}

Warning: This implementation will trigger swiftlints large_tuple rule. But you can disable, simply add ' - large_tuple' into disabled_rules section.