Simple Color Picker UIView for iOS

ColorPicker.swift

//
// Copyright (c) 2018 Bill Bonney <bill@communistech.com>. All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//

import UIKit

@objc protocol ColorPickerDelegate{
    func picked(color: UIColor)
}

class ColorPicker: UIView {

    var cursorColor = UIColor.white
    var cursorWidth = CGFloat(3.0)

    var _selectedColor = UIColor.black
    var selectedColor: UIColor {
        set {
            selectedColor(newValue)
        }
        get {
            return _selectedColor
        }
    }

    weak var delegate: ColorPickerDelegate?

    override func draw(_ rect: CGRect) {
        // Color Bar
        let width = Int(self.frame.size.width)
        for i in 0..<width {
            let xPosition = CGFloat(i)

            UIColor(hue: xPosition/self.frame.size.width, // convert to a value between 0.0 -> 1.0
                    saturation: 1.0,
                    brightness: 1.0,
                    alpha: 1.0).set()

            let colorBar = CGRect(x: xPosition, y: 0.0,
                                  width: 1.0, height: self.frame.size.height);
            UIRectFill(colorBar);
        }
        // Cursor Bar
        let positionX = getCursorPosition(forColor: selectedColor)
        cursorColor.set()
        let cursorBar = CGRect(x: positionX, y: 0.0, width: cursorWidth, height: self.frame.size.height)
        UIRectFill(cursorBar)
    }

    // Changes the selected color, updates the UI, and notifies the delegate.
    private func selectedColor(_ color: UIColor){
        if (color != selectedColor) {
            _selectedColor = color
            setNeedsDisplay()
            self.delegate?.picked(color: selectedColor)
        }
    }

    private func getCursorPosition(forColor color: UIColor) -> CGFloat {
        var hue: CGFloat = 0.0
        var saturation: CGFloat = 1.0
        var brightness: CGFloat = 1.0
        var alpha: CGFloat = 1.0

        if color.getHue(&hue, saturation: &saturation, brightness: &brightness, alpha: &alpha) {
            return CGFloat(hue * self.frame.size.width);
        }
        return 0.0
    }

    private func updateColor(_ touch: UITouch){
        let xPosition = touch.location(in: self).x

        if xPosition >= 0.0 && xPosition <= (frame.size.width-cursorWidth) {
            selectedColor = UIColor(hue: (xPosition / self.frame.size.width),
                                    saturation: 1.0, brightness: 1.0, alpha: 1.0)
            self.delegate?.picked(color: selectedColor)
            self.setNeedsDisplay()
        }
    }
}

extension ColorPicker {
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch =  touches.first {
            updateColor(touch)
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch =  touches.first {
            updateColor(touch)
        }
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch =  touches.first {
            updateColor(touch)
        }
    }
}