Blog: ObservableObjects and Protocols - ObservableObject in UIKit

blog--observableobject+protocols--observableobject-in-uikit.swift

// Copyright 2021 Expedia, Inc.
// SPDX-License-Identifier: Apache-2.0

import Combine
import UIKit

class DemoController: UIViewController {
    
    private let pricing: PricingProvider
    
    private var subscriptions = Set<AnyCancellable>()
    
    private lazy var stackView: UIStackView = {
        let view = UIStackView()
        view.alignment = .center
        view.axis = .vertical
        view.spacing = 8
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()
    
    private lazy var priceLabel: UILabel = {
        let label = UILabel()
        label.text = "Price not available"
        return label
    }()
    
    private lazy var fetchPriceButton: UIButton = {
        let button = UIButton()
        button.backgroundColor = UIColor(named: "ActionColor")
        button.contentEdgeInsets = UIEdgeInsets(top: 0, left: 24, bottom: 0, right: 24)
        button.layer.cornerRadius = 22;
        button.setTitle("Fetch price", for: .normal)
        button.addTarget(self, action: #selector(onTap), for: .touchUpInside)
        return button
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        stackView.addArrangedSubview(priceLabel)
        stackView.addArrangedSubview(fetchPriceButton)
        view.addSubview(stackView)
        
        NSLayoutConstraint.activate([
            fetchPriceButton.heightAnchor.constraint(equalToConstant: 44),
            stackView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            stackView.centerXAnchor.constraint(equalTo: view.centerXAnchor)
        ])
        
        subscribe()
    }
    
    init(pricing: PricingProvider) {
        self.pricing = pricing
        let bundle = Bundle(for: type(of: self))
        super.init(nibName: nil, bundle: bundle)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    @objc private func onTap() {
        pricing.fetch()
    }
    
    private func subscribe() {
        pricing.$price.sink { newPrice in
            guard let price = newPrice else {
                self.priceLabel.text = "Price not available"
                return
            }
            self.priceLabel.text = "\(price.amount) \(price.description)"
        }
        .store(in: &subscriptions)
    }
}