Part 2

Introduction

The idea for publishing came after reading the CSS translation for Swift: using styles for any subclass of UIView . The approach is quite interesting, but it was not very flexible, because does not allow combining styles of different types. Read more in the comments .

In this publication, an attempt will be made to obtain a more flexible way of defining styles, and examples will be given of using the resulting mechanism.

Scenery

We introduce the concept of scenery, which will personify imparting certain properties to an object:

typealias Decoration<T> = (T) -> Void 

 let decoration: Decoration<UIView> = { (view: UIView) -> Void in view.backgroundColor = UIColor.orange view.alpha = 0.5 view.isOpaque = true } let view = UIView() //  decoration(view) let label = UILabel() //  decoration(label) 

The advantages of using decorations over the usual imparting properties to an object:

• You can simultaneously give several properties to an object at once.
• The property is described once and does not require changes in all places of application of the decoration when refactoring (DRY)
• Less code and more visibility in the application of scenery
• Combining scenery by creating a decoration containing several other decorations
• Stylish trendy youth

Decorator and exmepleration methods

To apply the decoration, you must pass the instance to the decoration closure. However, a more natural process is passing the scenery to the instance method.

To solve this problem, you can use an intermediate - decorator. A decorator is a generic structure that has a pointer to an instance of a class to which decorations will be applied.

 struct Decorator<T> { let object: T } 

Using the generalized protocol for the decorated instance you can get a decorator. For publication purposes, the decorator will be available for an instance of any class inherited from UILabel.

 protocol DecoratorCompatible { associatedtype DecoratorCompatibleType var decorator: Decorator<DecoratorCompatibleType> { get } } extension DecoratorCompatible { var decorator: Decorator<Self> { return Decorator(object: self) } } extension UILabel: DecoratorCompatible {} 

Let us complement the structure of the decorator with the instance method that will receive the decorations. It is worth paying attention that the scenery will be applied in the sequence in which they will be transferred to the decorator. This applies to cases where several decorations change the same property of an object.

 struct Decorator<T> { let object: T func apply(_ decorations: Decoration<T>...) -> Void { decorations.forEach({ $0(object) }) } } 

Example

For publishing purposes, a repository has been created on github , which contains an example of usage. Installation via cocoapods : pod 'Decorator' is also available.

First, you should create a set of necessary decorations in any convenient way. For example, like this:

 struct Style { static var fontNormal: Decoration<UILabel> { return { (view: UILabel) -> Void in view.font = UIFont.systemFont(ofSize: 14.0) } } static var fontTitle: Decoration<UILabel> { return { (view: UILabel) -> Void in if #available(iOS 8.2, *) { view.font = UIFont.systemFont(ofSize: 17.0, weight: UIFontWeightBold) } else { view.font = UIFont.boldSystemFont(ofSize: 17.0) } } } static func corners(rounded: Bool) -> Decoration<UIView> { return { [rounded] (view: UIView) -> Void in switch rounded { case true: let mask = CAShapeLayer() let size = CGSize(width: 10, height: 10) let rect = view.bounds let path = UIBezierPath(roundedRect: rect, byRoundingCorners: .allCorners, cornerRadii: size) mask.path = path.cgPath view.layer.mask = mask default: view.layer.mask = nil } } } } 

It is worth paying attention to the fact that the scenery is represented by two types:

 Decoration<UIView> Decoration<UILabel> 

Both types can be applied simultaneously, although they will be applied to an object of the UILabel class. The use of decorations through the decorator is as follows:

 let labelNormal = UILabel() labelNormal.decorator.apply(Style.fontNormal, Style.corners(rounded: false)) let labelTitle = UILabel() labelNormal.decorator.apply(Style.fontTitle, Style.corners(rounded: true)) 

Conclusion

The approach turned out to be more flexible than in the translation of the article , since managed to achieve the use of different styles at the same time. If you have ideas for improving the approach - comments are welcome. Thanks for attention.

Part 2