UIKit and Decorator Design Pattern

How to use UIkit in SwiftUI

In this series of “Design patterns for iOS“, our senior iOS Developer, Andrey Soloviev, will go through all common design patterns and show you how to use UIkit in SwiftUI. He will also adhere to Swift’s best practices and point them out.

Design patterns are general solutions to commonly occurring problems that give you more freedom and confidence in choosing solutions to a specific problem. 

I don’t like to store references to objects that I don’t really use. If we have many decorators then we would have to create an additional property for each of them and the code gets harder to read and maintain.

We can also create an array or set of such objects and store them all there, so they will be deallocated together with HyperlinkViewController.

class HyperlinkViewController: UIViewController {
@IBOutlet weak var hyperLabel: UILabel!
var decorators = [Any]()
override func viewDidLoad() {
super.viewDidLoad()
let hyperlinkDecorator = HyperlinkDecorator(label: hyperLabel)
hyperlinkDecorator.url = URL(string: “https://medium.com”)
decorators.append(hyperlinkDecorator)
}
}

It may look better but I don’t like it either. That’s how I came to the next solution that I still use to get rid of such references by working with UIKit components.

We subclass HyperlinkDecorator from UIView, make it zero size and add it as a subview of UILabel, so it will live and die together with UILabel.

We also set a weak reference to UILabel to avoid retain cycle and memory leaks

import UIKit

class HyperlinkDecorator: UIView {
var url: URL?
weak var label: UILabel?

required init(label: UILabel) {
self.label = label
super.init(frame: .zero)
label.isUserInteractionEnabled = true
label.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(hyperlinkedLabelTapped)))
label.addSubview(self)
}

// It’s required for UIView subclasses
required init?(coder: NSCoder) {
fatalError(“init(coder:) has not been implemented”)
}

@objc private func hyperlinkedLabelTapped() {
if let url = url, UIApplication.shared.canOpenURL(url) {
UIApplication.shared.open(url)
}
}
}

There is generic function subview(type:) that searches for the subview of a specific type. I could use tag but I prefer this version as the code looks cleaner and we don’t need to worry about assigning unique tag value. And that’s how we can use it now.

class HyperlinkViewController: UIViewController {
@IBOutlet weak var hyperLabel: UILabel!

override func viewDidLoad() {
super.viewDidLoad()
hyperLabel.url = URL(string: “https://medium.com”)
}
}

Now it looks much better and I would actually stop here, but still can refactor the UILabel extension and make it easier to add new properties and new decorators.

That’s what I’m going to do:

• Move subview(type:) to the UIView extension
• Add ViewDecorator protocol
• Add another generic function viewDecorator(type:) to the UIView extension that would search and create a new decorator if it’s not found.
• Conforms HyperlinkDecorator to ViewDecorator protocol
• UILabel extension

It seems not many changes, let’s do it.

Moving function subview(type:) to UIView:

import UIKit

extension UIView {
func subview(type: V.Type = V.self ) -> V? {
return subviews.first(where: { $0 is V }) as? V
}
}

Now let’s move code of searching and creation of new decorator from UILabel extension to separate generic function inside UIView extension:

import UIKit

extension UIView {
func viewDecorator(type: V.Type = V.self) -> V {
return subview(type: V.self) ?? V(object: self as! V.View)
}
}

This function works exactly the same as before only now it’s generic. If you’re unable to understand how it works, please read more about generics.

Conforming HyperlinkDecorator to ViewDecorator is simple, just add protocol confirmation and replace init(label:) with init(object:)

Here’s the complete code for HyperlinkDecorator

import UIKit

class HyperlinkDecorator: UIView, ViewDecorator {
var url: URL?
weak var label: UILabel?

required init(object label: UILabel) {
self.label = label
super.init(frame: .zero)
label.isUserInteractionEnabled = true
label.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(hyperlinkedLabelTapped)))
label.addSubview(self)
}

// It’s required to have for UIView subclasses
required init?(coder: NSCoder) {
fatalError(“init(coder:) has not been implemented”)
}

@objc private func hyperlinkedLabelTapped() {
if let url = url, UIApplication.shared.canOpenURL(url) {
UIApplication.shared.open(url)
}
}
} 

And finally updated extension of UILabel, the reason for all of these steps.
That’s it, that’s all. You can find the complete example project here.

import UIKit

extension UILabel {
var url: URL? {
get { viewDecorator(type: HyperlinkDecorator.self).url }
set { viewDecorator(type: HyperlinkDecorator.self).url = newValue }
}
}