Convenience Initializer used in swift as a supporting initializer. By using the convenience initializer you can put multiple -init along with other and use whichever you want to use.

convenience initializers have the convenience keyword before the -init method. There is no need to have convenience initializers compulsory defined when the class does not require initializers.

A convenience initializer must call another initializer from the same class. It is considered as a supporting initializer for a class. we can understand it by using the following example -

Suppose we have an extension class of UIColor and here we will use the -init methods by using convenience keyword-

extension UIColor {

     convenience init(red: Int, green: Int, blue: Int) {
        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)
    }
    
      convenience init(hexString:String) {

        let hexString:NSString =  hexString.trimmingCharacters(in: CharacterSet.whitespaces) as NSString
        let scanner            = Scanner(string: hexString as String)
        
        if (hexString.hasPrefix("#")) {
            scanner.scanLocation = 1
        }
        
        var color:UInt32 = 0
        scanner.scanHexInt32(&color)
        
        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask
        
        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0
        
        self.init(red:red, green:green, blue:blue, alpha:1)
    }
}

The above example defines the use of convenience initializer.