【Code Review Challenge】解説3問目：実行タイミングには気をつけて #try! Swift Tokyo 2024

import UIKit
import StoreKit

// Check if there is a promotional app at the launch of the application by querying the server.
// If there is a promotional app, display PromotionStoreViewController modally.
final class AppTopViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        Task {
            await downloadPromotionAppInfo(url: URL(string: "https://example.com/promotionapp/info")!)
        }
    }

    private func downloadPromotionAppInfo(url: URL) async {
        guard let (data, response) = try? await URLSession.shared.data(from: url) else { return }

        guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
            print("Invalid response")
            return
        }

        // json = ["appId": AppID of the promotional app (String),
        //         "appTitle": Name of the promotional app (String),
        //         "appIconImage": Image data of the promotional app (Data)]
        if let jsonObject = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
            let viewController = PromotionStoreViewController()
            viewController.appId = jsonObject["appId"] as? String
            viewController.appTitleLabel.text = jsonObject["appTitle"] as? String
            if let imageData = jsonObject["appIconImage"] as? Data {
                viewController.appIconImageView.image = UIImage(data: imageData)
            }
            self.present(viewController, animated: true)
        }
    }

    // The rest of the code is omitted
}

final class PromotionStoreViewController: UIViewController {
    var appId: String?
    @IBOutlet var appTitleLabel: UILabel!
    @IBOutlet var appIconImageView: UIImageView!
    @IBOutlet var showAppStoreButton: UIButton!

    @IBAction private func didTapPresentStoreViewButton(sender: Any) {
        let storeViewController = SKStoreProductViewController()
        let parameters: [String: Any] = [SKStoreProductParameterITunesItemIdentifier: appId]
        storeViewController.loadProduct(withParameters: parameters) { status, error in
            if status {
                self.present(storeViewController, animated: true)
            } else {
                print(error!.localizedDescription)
            }
        }
    }
}

@MainActor
class UIViewController : UIResponder

final class AppTopViewController: UIViewController {
     ...
    private func downloadPromotionAppInfo(url: URL) async {
        ... 
        if let jsonObject = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
            let viewController = PromotionStoreViewController()
            viewController.appId = jsonObject["appId"] as? String
            viewController.appTitleLabel.text = jsonObject["appTitle"] as? String
            if let imageData = jsonObject["appIconImage"] as? Data {
                viewController.appIconImageView.image = UIImage(data: imageData)
            }
            self.present(viewController, animated: true)
        }
        ...
}

...

// downloadPromotionAppInfo(url:)に@MainActorをつける
@MainActor
private func downloadPromotionAppInfo(url: URL) async {
    ...
}

// DispatchQueue.main.asyncでpresentを実行する
private func downloadPromotionAppInfo(url: URL) async {
    ...
    if let jsonObject = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
        let viewController = PromotionStoreViewController()
        ...
        DispatchQueue.main.async {
            self?.present(viewController, animated: true)
        }
    }             
}

final class AppTopViewController: UIViewController {
     ...
    private func downloadPromotionAppInfo(url: URL) async {
        ... 
        if let jsonObject = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
           ...
            viewController.appTitleLabel.text = jsonObject["appTitle"] as? String
            if let imageData = jsonObject["appIconImage"] as? Data {
                viewController.appIconImageView.image = UIImage(data: imageData)
            }
            self.present(viewController, animated: true)
        }
        ...
}

final class PromotionStoreViewController: UIViewController {
    ...
    @IBOutlet var appTitleLabel: UILabel!
    @IBOutlet var appIconImageView: UIImageView!
    ...
}

// IBOutletをprivateにし、viewDidLoadでパラメータを設定する。
final class AppTopViewController: UIViewController {
     ...
    private func downloadPromotionAppInfo(url: URL) async {
        ... 
        if let jsonObject = try? JSONSerialization.jsonObject(with: data) as? [String: Any] {
           ...
            viewController.appTitle = jsonObject["appTitle"] as? String
            if let imageData = jsonObject["appIconImage"] as? Data {
                viewController.appIconImage= UIImage(data: imageData)
            }
            self.present(viewController, animated: true)
        }
        ...
}

final class PromotionStoreViewController: UIViewController {
    ...
    var appTitle: String?
    var appIconImage: UIImage?
    @IBOutlet private var appTitleLabel: UILabel!
    @IBOutlet private var appIconImageView: UIImageView!
    ...
    override func viewDidLoad() {
        super.viewDidLoad()

        appTitleLabel.text = appTitle
        appIconImageView.image = appIconImage 
    }
}