Extensions in Swift allow us to add methods to existing objects (class, struct, enum and protocol). They are similar to categories in Objective-C.
Let’s extend UIColor class with custom convenience initialiser to create color with hex value:
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extension UIColor {
/// Returns color with given hex integer value
convenience init(hex: Int, alpha: CGFloat = 1.0) {
let r = CGFloat((hex & 0xff0000) >> 16) / 255.0
let g = CGFloat((hex & 0x00ff00) >> 8) / 255.0
let b = CGFloat((hex & 0x0000ff) >> 0) / 255.0
self.init(red: r, green: g, blue: b, alpha: alpha)
}
}
Now we can create colors in this way:
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let color1 = UIColor(hex: 0x1abc9c, alpha: 0.5)
let color2 = UIColor(hex: 0x112233)
We can also add methods and read-only properties to instances of UIColor class:
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extension UIColor {
/// Returns hex string color representation
func toHexString(prefix: String = "#") -> String {
String(format:"\(prefix)%06x", asInt)
}
/// Returns integer color representation
var asInt: Int {
var r: CGFloat = 0, g: CGFloat = 0, b: CGFloat = 0, a: CGFloat = 0
getRed(&r, green: &g, blue: &b, alpha: &a)
return (Int)(r * 255) << 16 | (Int)(g * 255) << 8 | (Int)(b * 255) << 0
}
}
New methods asInt and asHexString now available for any UIColor instance:
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let myRed = UIColor(hex: 0x991122) // r 0,6 g 0,067 b 0,067 a 1,0
let intValue = myRed.asInt // 10031377
let cssColor = myRed.toHexString() // "#991122"
Static (or class) methods and read-only properties can be defined in extensions as well:
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extension UIColor {
static var myRed: Color { UIColor(hex: 0xAA0000) }
}
Usage:
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let myColor = UIColor.myRed