Override UIButton backgroundColor property with protocol - swift3

Question

I have a protocol like
protocol ButtonPresentable {
var backgroundColor: UIColor { get }
}
extension ButtonPresentable {
var backgroundColor: UIColor? {
return UIColor.red
}
}
I have a button custom class (draw with IB) that implements my protocol
class MyButton: UIButton, ButtonPresentable {
}
Why this protocol doesn't 'override' native backgroundColor property ?
I would like to have a default protocol implementation that will set a default background to all buttons. Is there a protocol oriented way to set default values to all UIButton background colors ?
EDIT: Actually I do that
protocol ButtonPresentable {
var pBackgroundColor: UIColor { get }
}
extension ButtonPresentable {
var pBackgroundColor: UIColor? {
return UIColor.red
}
func applyTheme() {
self.backgroundColor = pBackgroundColor
}
}
// In my custom view
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)!
self.applyTheme()
}

Answer 1

1. Why this protocol doesn't 'override' native backgroundColor property ?
Because: Extensions can add new functionality to a type, but they cannot override existing functionality.
Look at this example:
protocol ButtonProtocol {
var name: String { get }
}
extension ButtonProtocol {
var name: String {
return "button protocol"
}
}
class ButtonClass: ButtonProtocol {
var name: String = "button class"
}
let button = ButtonClass()
print(button.name) // prints: button class
2. Is there a protocol oriented way to set default values to all UIButton background colors ?
And if you want to override the backgroundColor of all buttons you could do this: once the button is set with its frame, you can override its background color:
extension UIButton {
open override var frame: CGRect {
didSet {
self.backgroundColor = .red
}
}
}