Hello folks, Leo here.
Today we’ll discuss the most famous communication pattern in Swift/iOS development: the delegation pattern.
The delegation pattern is very simple if we try to imagine it is just a delegation process in the real world.
It’s a ONE TO ONE communication pattern, which means if we are trying to communicate to/from more than ONE receiver/sender this isn’t the best way to do that.
Example: Imagine that you are hungry and have a friend that went out to buy some food. You can ask (delegate) him to bring you food.
In swift, we can do the same.
If we have a Screen A that needs data from Screen B, we can simply create a delegation communication pattern between them.
Let’s go to the code!
Example: Imagine that we have a CardView’s data that we need in the HomeViewController. The full code example is the end of the post.
1 – First, create a protocol in which the views will communicate. This protocol says: “Well I’m waiting for some input from somewhere”.
2 – Conform to the protocol HomeViewControllerDelegate.protocol HomeViewControllerDelegate: class { func setDataReceivedFromCard(data: String) } class HomeViewController: ViewController { // the HomeViewController Configuration ... }
3 – Now, in CardView, we’ll have to set how we will send the HomeViewController to CardView. You have two basic ways: first one is using the init method and the second one is using a func. Remember that to avoid RETAINING CICLES the delegate variable should aways be WEAK.extension HomeViewController: HomeViewControllerDelegate { func setDataReceivedFromCard(data: String) { print("data is back to the previous view") dataLabel.text = data // imagine that we have to set the data on a label } }
4 – In CardView call the delegate var method with the data we want to send back.weak private var delegate: MyViewControllerDelegate? // we can set the delegate here init(delegate: MyViewControllerDelegate?) { super.init(frame: .zero) self.delegate = delegate } //OR // we can use a func to the delegate func set(delegate: MyViewControllerDelegate) { self.delegate = delegate }
5 – Back to HomeViewController, don’t forget to set the self to the CardView when configuring UI / or whatever fits for you.@objc func sendDataToOtherViewTapped() { // in this example this is an action triggered by a button print ("send data to other view") delegate?.setDataReceivedFromCard(data: "Data from card is: Apple") }
That’s all folks! The full code example below can be executed in Swift Playground:func configureCardView() { view.addSubview(cardView) cardView.translatesAutoresizingMaskIntoConstraints = false cardView.backgroundColor = .black cardView.set(delegate: self) // DON'T FORGET THIS!!!!! }
import UIKit import PlaygroundSupport protocol HomeViewControllerDelegate: class { func setDataReceivedFromCard(data: String) } class HomeViewController : UIViewController { let cardView = Card() let animationButton = UIButton(type: .system) let dataLabel = UILabel() var cardShow = false override func loadView() { let view = UIView() view.backgroundColor = .white self.view = view } override func viewDidLoad() { super.viewDidLoad() configureAnimationButton() configureCardView() } func configureCardView() { view.addSubview(cardView) cardView.translatesAutoresizingMaskIntoConstraints = false cardView.backgroundColor = .black cardView.set(delegate: self) view.addSubview(dataLabel) dataLabel.translatesAutoresizingMaskIntoConstraints = false dataLabel.font = UIFont.systemFont(ofSize: 20, weight: .bold) NSLayoutConstraint.activate([ cardView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.5), cardView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.9), cardView.centerYAnchor.constraint(equalTo: view.centerYAnchor), cardView.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 1000), dataLabel.topAnchor.constraint(equalTo: animationButton.bottomAnchor, constant: 15), dataLabel.heightAnchor.constraint(equalToConstant: 30), dataLabel.centerXAnchor.constraint(equalTo: animationButton.centerXAnchor) ]) } func configureAnimationButton() { view.addSubview(animationButton) animationButton.translatesAutoresizingMaskIntoConstraints = false animationButton.setTitle("Animate", for: .normal) animationButton.layer.cornerRadius = 10 animationButton.backgroundColor = .systemGreen animationButton.setTitleColor(.label, for: .normal) animationButton.titleLabel?.font = .systemFont(ofSize: 36, weight: .bold) animationButton.addTarget(self, action: #selector(animateButton), for: .touchUpInside) print("será?") NSLayoutConstraint.activate([ animationButton.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20), animationButton.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -20), animationButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 20), animationButton.heightAnchor.constraint(equalToConstant: 50) ]) } @objc func animateButton() { if !cardShow { UIView.animate(withDuration: 0.2) { [weak self] in self?.cardView.transform = CGAffineTransform(translationX: -1000, y: 0) } } else { UIView.animate(withDuration: 0.4) { [weak self] in self?.cardView.transform = CGAffineTransform(translationX: 1000, y: 0) } } cardShow.toggle() } } extension HomeViewController: HomeViewControllerDelegate { func setDataReceivedFromCard(data: String) { print("data is back to the previous view") dataLabel.text = data } } class Card: UIView { override init(frame: CGRect) { super.init(frame: frame) configureUI() } required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") } weak private var delegate: HomeViewControllerDelegate? // you can set the delegate here init(delegate: HomeViewControllerDelegate?) { super.init(frame: .zero) self.delegate = delegate } //OR // you can use a func to the delegate func set(delegate: HomeViewControllerDelegate) { self.delegate = delegate } func configureUI() { let sendDataToSuperViewButton = UIButton(type: .roundedRect) addSubview(sendDataToSuperViewButton) sendDataToSuperViewButton.translatesAutoresizingMaskIntoConstraints = false sendDataToSuperViewButton.backgroundColor = .systemBlue sendDataToSuperViewButton.setTitle("Send data to Super view", for: .normal) sendDataToSuperViewButton.setTitleColor(.black, for: .normal) sendDataToSuperViewButton.addTarget(self, action: #selector(sendDataToOtherViewTapped), for: .touchUpInside) sendDataToSuperViewButton.layer.cornerRadius = 10 NSLayoutConstraint.activate([ sendDataToSuperViewButton.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -15), sendDataToSuperViewButton.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 15), sendDataToSuperViewButton.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -15), sendDataToSuperViewButton.heightAnchor.constraint(equalToConstant: 50) ]) } @objc func sendDataToOtherViewTapped() { print("send data to other view") delegate?.setDataReceivedFromCard(data: "Data from card is: Apple") } } PlaygroundPage.current.liveView = HomeViewController()
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