ios – 类型’String’的值没有成员’stringByTrimmingCharactersInSet’

extension UIColor {
    convenience init (hex:String) {
        var cString:String = hex.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet()).uppercased() // error appears on this line

        if (cString.hasPrefix("#")) {
            cString = (cString as Nsstring).substring(from: 1)
        }



        let rString = (cString as Nsstring).substring(to: 2)
        let gString = ((cString as Nsstring).substring(from: 2) as Nsstring).substring(to: 2)
        let bString = ((cString as Nsstring).substring(from: 4) as Nsstring).substring(to: 2)

        var r:CUnsignedInt = 0,g:CUnsignedInt = 0,b:CUnsignedInt = 0;
        Scanner(string: rString).scanHexInt32(&r)
        Scanner(string: gString).scanHexInt32(&g)
        Scanner(string: bString).scanHexInt32(&b)


        self.init(red: CGFloat(r) / 255.0,green: CGFloat(g) / 255.0,blue: CGFloat(b) / 255.0,alpha: CGFloat(1))
    }
}

我猜这个错误是由于’stringByTrimmingCharactersInSet’的语法变化而导致的.这个更正是什么？