How to create a UIColor from a String like "rgb(0,0,0)"?

Question

I have a string from server in a format like "rgb(0,0,0)", which should be used on some UI elements.

The main problem is the various colours like "rgb(20,120,4)" etc.

Is there a way to parse it in something like UIColor(red: 0, green: 0, blue: 0, alpha: 1)?

Answer 1

There are so many possible solutions! Here is one using NSScanner:

extension UIColor {
    convenience init?(rgbString : String) {
        var red = 0.0
        var green = 0.0
        var blue = 0.0
        
        let scanner = NSScanner(string : rgbString)
        guard scanner.scanString("rgb(", intoString: nil)
            && scanner.scanDouble(&red)
            && scanner.scanString(",", intoString: nil)
            && scanner.scanDouble(&green)
            && scanner.scanString(",", intoString: nil)
            && scanner.scanDouble(&blue)
            && scanner.scanString(")", intoString: nil) else {
                return nil
        }
        self.init(red: CGFloat(red/255.0), green: CGFloat(green/255.0), blue: CGFloat(blue/255.0), alpha: 1.0)
    }
}

Usage example:

if let col = UIColor(rgbString: "rgb(20,120.5, 4)") {
    print(col)
} else {
    print("invalid color specification")
}

Update for Swift 3/4:

extension UIColor {
    convenience init?(rgbString: String) {
        var red = 0.0
        var green = 0.0
        var blue = 0.0
        
        let scanner = Scanner(string: rgbString)
        guard scanner.scanString("rgb(", into: nil)
            && scanner.scanDouble(&red)
            && scanner.scanString(",", into: nil)
            && scanner.scanDouble(&green)
            && scanner.scanString(",", into: nil)
            && scanner.scanDouble(&blue)
            && scanner.scanString(")", into: nil) else {
                return nil
        }
        self.init(red: CGFloat(red/255.0), green: CGFloat(green/255.0), blue: CGFloat(blue/255.0), alpha: 1.0)
    }
}

Update for Swift 5:

extension UIColor {
    convenience init?(rgbString: String) {

        let scanner = Scanner(string: rgbString)
        guard scanner.scanString("rgb(") != nil,
              let red = scanner.scanDouble(),
              scanner.scanString(",") != nil,
              let green = scanner.scanDouble(),
              scanner.scanString(",") != nil,
              let blue = scanner.scanDouble(),
              scanner.scanString(")") != nil else {
                return nil
        }
        self.init(red: CGFloat(red/255.0), green: CGFloat(green/255.0), blue: CGFloat(blue/255.0), alpha: 1.0)
    }
}