Hex and UIColor mutual conversion in Swift

There is a feeling of force, but it's okay because it works () ().

UIColor+Hex.swift

import Foundation
import UIKit

extension UIColor {
    convenience init(hex: String, alpha: CGFloat = 1.0) {
        let v = Int("000000" + hex.replacingOccurrences(of: "#", with: ""), radix: 16) ?? 0
        let r = CGFloat(v / Int(powf(256, 2)) % 256) / 255
        let g = CGFloat(v / Int(powf(256, 1)) % 256) / 255
        let b = CGFloat(v / Int(powf(256, 0)) % 256) / 255
        self.init(red: r, green: g, blue: b, alpha: min(max(alpha, 0), 1))
    }

    func toHexString() -> String {
        var red: CGFloat     = 1.0
        var green: CGFloat   = 1.0
        var blue: CGFloat    = 1.0
        var alpha: CGFloat   = 1.0
        self.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
        
        let r = Int(String(Int(floor(red*100)/100 * 255)).replacingOccurrences(of: "-", with: ""))!
        let g = Int(String(Int(floor(green*100)/100 * 255)).replacingOccurrences(of: "-", with: ""))!
        let b = Int(String(Int(floor(blue*100)/100 * 255)).replacingOccurrences(of: "-", with: ""))!
                
        let res = String(r, radix: 16).leftPadding(toLength: 2, withPad: "0") + String(g, radix: 16).leftPadding(toLength: 2, withPad: "0") + String(b, radix: 16).leftPadding(toLength: 2, withPad: "0")
        return res
    }
}
extension String {

      func leftPadding(toLength: Int, withPad: String) -> String {
        let stringLength = self.count
        if stringLength < toLength {
            return String(repeating:withPad, count: toLength - stringLength) + self
        } else {
            return String(self.suffix(toLength))
        }
    }
} 

How to use

// hex to UIColor
let color = UIColor(hex:"#565656")

// UIColor to hex
print(color.toHexString())