Easily apply theme styles to any UIView!

Theming.swift

Make the following possible!

MarvelTheme.TextStyle.CommicSans.apply(to: label)
MarvelTheme.ColorStyle.dangerColor.apply(to: label)

// ============================== StylableView protocol ==============================
// Adds a consistent styling API to any UIView. 
// The example here allows for any UIView subclass to have a way of setting its font type.

protocol StylableView {
    func apply(font: UIFont?)
}


extension UIView : StylableView {
    //we can't really add this as a StylableView extension because 
    //the views are being styled as StylableView, and even if the subclasses
    //override the default implementation, they won't be recognized.
    func apply(font: UIFont?) {}  
}

extension UILabel {
    override func apply(font: UIFont?) {
        self.font = font
    }
}

extension UIButton {
    override func apply(font: UIFont?) {
        titleLabel?.font = font
    }
}

//Now we have a consistent way of setting font of both labels and buttons.

struct UIViewStyle {

    let styling: (StylableView) -> ()

    func apply(to stylabelView: StylableView) {
        styling(stylabelView)
    }
    
    static func compose(styles: UIViewStyle...) -> UIViewStyle {
        return UIViewStyle {
            for style in styles {
                style.apply(to: $0)
            }
        }
    }
    
}

// Basic example view
let whiteStyle = UIViewStyle { ($0 as? UIView)?.backgroundColor = .white } //We can improve this with a consistent API
let blueStyle = UIViewStyle { ($0 as? UIView)?.backgroundColor = .blue }

let v = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
whiteStyle.apply(to: v)
v // background becomes white

blueStyle.apply(to: v)
v // background becomes blue

let h1 = UIViewStyle { $0.apply(font: UIFont(name: "ComicSansRegular", size: 10)) }
h1.apply(to: UIView()) //Does nothing because the UIView method is empty.
h1.apply(to: UILabel() //Applies the CommicSansRegular font to the label
 
============================== Theming ==============================

protocol ColorStylable {
    static var mainColor: UIViewStyle { get }
}

protocol TextStylable {
    static var mainColor: UIViewStyle { get }
}

protocol Themable {
    static var ColorStyle: ColorStylable.Type { get }
    static var TextStyle: TextStylable.Type { get }
}

struct MarvelColorStyle : ColorStylable {
    static let mainColor = UIViewStyle { ($0 as? UIView)?.backgroundColor = .red }
}

struct MarvelTextStyle: TextStylable {}

struct MarvelTheme : Themable {
    static var TextStyle: TextStylable.Type = MarvelTextStyle.self
    static var ColorStyle: ColorStylable.Type = MarvelColorStyle.self
}

let theme = MarvelTheme.self
theme.ColorStyle.mainColor.apply(to: v)
v

============================================ Examples =====================================

let courierNewPSBold = UIViewStyle { $0.apply(font: UIFont(name: "CourierNewPS-BoldMT", size: 15)) }
let papyrus = UIViewStyle { $0.apply(font: UIFont(name: "Papyrus-Condensed", size: 20)) }

let blueText = UIViewStyle { $0.apply(textColor: .blue) }
let greenText = UIViewStyle { $0.apply(textColor: .green) }

let courierNewPSBoldBlue = UIViewStyle.compose(styles: courierNewPSBold, blueText)
let papyrusGreen = UIViewStyle.compose(styles: papyrus, greenText)

let label = UILabel()
v.addSubview(label)
label.text = "Some text"
label.frame = CGRect(x: 10, y: 10, width: 80, height: 80)
courierNewPSBoldBlue.apply(to: label)
v

papyrusGreen.apply(to: label)
v