Swift扩展UIColor

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import Foundation
import UIKit

extension UIColor {
    
    convenience init(hex: String) {
        self.init(hex: hex, alpha: 1)
    }
    
    convenience init(hex: String, alpha: CGFloat) {
        let scanner = Scanner(string: hex)
        scanner.scanLocation = 0
        var rgbValue: UInt64 = 0
        scanner.scanHexInt64(&rgbValue)
        
        let r = (rgbValue & 0xff0000) >> 16
        let g = (rgbValue & 0xff00) >> 8
        let b = rgbValue & 0xff
        
        self.init(
            red: CGFloat(r) / 0xff,
            green: CGFloat(g) / 0xff,
            blue: CGFloat(b) / 0xff,
            alpha: alpha
        )
    }
    
    convenience init(red: Int, green: Int, blue: Int) {
        self.init(red: red, green: green, blue: blue, alpha: 1)
    }
    
    convenience init(red: Int, green: Int, blue: Int, alpha: CGFloat) {
        assert(red >= 0 && red <= 255, "Invalid red component")
        assert(green >= 0 && green <= 255, "Invalid green component")
        assert(blue >= 0 && blue <= 255, "Invalid blue component")
        self.init(
            red: CGFloat(red) / 255.0,
            green: CGFloat(green) / 255.0,
            blue: CGFloat(blue) / 255.0,
            alpha: 1.0
        )
    }
    
    static func random() -> UIColor {
        return UIColor(red: .random(), green: .random(), blue: .random(), alpha: 0.7)
    }
    
}

import UIKit

extension UIFont {
    class func defaultFont(size: CGFloat) -> UIFont {
        return UIFont(name: "Helvetica", size: size) ?? UIFont.systemFont(ofSize: size)
    }
}