SwiftのDelegateを初心者がマスターするための9選の手法

// DelegateのProtocolを定義
protocol ActionCompletedDelegate: AnyObject {
    func actionDidComplete()
}

class TaskManager {
    weak var delegate: ActionCompletedDelegate?

    func performTask() {
        // 何らかのタスクの実行
        // ...

        // タスク完了後、Delegateメソッドを呼び出し
        delegate?.actionDidComplete()
    }
}

protocol DataManagerDelegate: AnyObject {
    func dataDidLoad(data: [String])
}

class DataManager {
    weak var delegate: DataManagerDelegate?

    func loadData() {
        // 仮のデータをロードする
        let data = ["apple", "banana", "cherry"]

        // データロード完了後、Delegateメソッドを呼び出し
        delegate?.dataDidLoad(data: data)
    }
}

protocol SettingsDelegate: AnyObject {
    func didUpdateSettings(value: String)
}

class SettingsViewController: UIViewController {
    weak var delegate: SettingsDelegate?

    @IBAction func saveButtonTapped(_ sender: Any) {
        let inputValue = "Sample Data" // ここでは仮のデータを使用
        delegate?.didUpdateSettings(value: inputValue)
    }
}

class MainViewController: UIViewController, SettingsDelegate {
    func didUpdateSettings(value: String) {
        print("設定が更新されました: \(value)")
    }
}

import UIKit

class TableViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
    var items = ["item1", "item2", "item3"]

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return items.count
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
        cell.textLabel?.text = items[indexPath.row]
        return cell
    }
}

import UIKit

class TextFieldViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var textField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        textField.delegate = self
    }

    func textFieldDidEndEditing(_ textField: UITextField) {
        if let text = textField.text {
            print("入力内容: \(text)")
        }
    }
}

import UIKit

protocol SampleDelegate: AnyObject {
    func didTapButton()
}

class SampleViewController: UIViewController {
    weak var delegate: SampleDelegate?

    @IBAction func buttonTapped(_ sender: UIButton) {
        delegate?.didTapButton()
    }
}

class ParentViewController: UIViewController, SampleDelegate {
    let sampleVC = SampleViewController()

    func setup() {
        // ここでDelegateのセットアップを忘れている
        self.present(sampleVC, animated: true, completion: nil)
    }

    func didTapButton() {
        print("ボタンがタップされました。")
    }
}

func setup() {
    sampleVC.delegate = self
    self.present(sampleVC, animated: true, completion: nil)
}

import UIKit

protocol SampleDelegate: AnyObject {
    func didTapButton()
}

class MultiDelegate: SampleDelegate {
    private var delegates: [SampleDelegate] = []

    func addDelegate(delegate: SampleDelegate) {
        delegates.append(delegate)
    }

    func didTapButton() {
        delegates.forEach { $0.didTapButton() }
    }
}

class ViewController: UIViewController {
    let multiDelegate = MultiDelegate()

    func setup() {
        let firstDelegate: SampleDelegate = FirstClass()
        let secondDelegate: SampleDelegate = SecondClass()

        multiDelegate.addDelegate(delegate: firstDelegate)
        multiDelegate.addDelegate(delegate: secondDelegate)

        // 何らかの操作でdidTapButtonを呼び出す
        multiDelegate.didTapButton()
    }
}

class FirstClass: SampleDelegate {
    func didTapButton() {
        print("FirstClassでボタンがタップされました。")
    }
}

class SecondClass: SampleDelegate {
    func didTapButton() {
        print("SecondClassでボタンがタップされました。")
    }
}

import UIKit

protocol DangerousDelegate: AnyObject {
    func didTriggerEvent()
}

class DangerousViewController: UIViewController {
    var delegate: DangerousDelegate? // ここでstrong referenceを持ってしまっている
    ...
}

import UIKit

protocol ButtonTapDelegate: AnyObject {
    func buttonDidTap(sender: UIButton)
}

class ButtonViewController: UIViewController {
    weak var delegate: ButtonTapDelegate?

    @IBAction func buttonTapped(_ sender: UIButton) {
        delegate?.buttonDidTap(sender: sender)
    }
}

protocol UserActionDelegate: AnyObject {
    func didTapSaveButton(data: String)
}

class UserViewController: UIViewController {
    weak var actionDelegate: UserActionDelegate?

    @IBAction func saveButtonTapped(_ sender: UIButton) {
        let data = "ユーザーデータ"
        actionDelegate?.didTapSaveButton(data: data)
    }
}

protocol DataFetchingDelegate: AnyObject {
    func didFetchData(data: String, error: Error?)
}

class DataFetcher {
    weak var fetchDelegate: DataFetchingDelegate?

    func fetchData() {
        // 非同期処理の模擬
        DispatchQueue.global().async {
            let data = "非同期で取得したデータ"
            // 完了後、メインスレッドでDelegateに結果を伝える
            DispatchQueue.main.async {
                self.fetchDelegate?.didFetchData(data: data, error: nil)
            }
        }
    }
}

protocol ErrorHandlerDelegate: AnyObject {
    func didCompleteTask(withError error: Error?)
}

class TaskHandler {
    weak var errorDelegate: ErrorHandlerDelegate?

    func performTask() {
        // タスク実行の模擬
        DispatchQueue.global().async {
            // エラーを模擬的に生成
            let error = NSError(domain: "TaskError", code: 1001, userInfo: nil)
            // 完了後、メインスレッドでDelegateにエラー情報を伝える
            DispatchQueue.main.async {
                self.errorDelegate?.didCompleteTask(withError: error)
            }
        }
    }
}

protocol UIStateDelegate: AnyObject {
    func didChangeState(to state: UIState)
}

enum UIState {
    case loading, empty, filled
}

class MainViewController: UIViewController {
    weak var uiStateDelegate: UIStateDelegate?

    func loadData() {
        // データ取得の模擬
        let isDataAvailable = true

        if isDataAvailable {
            uiStateDelegate?.didChangeState(to: .filled)
        } else {
            uiStateDelegate?.didChangeState(to: .empty)
        }
    }
}

protocol DataMergeDelegate: AnyObject {
    func didMergeData(result: [String])
}

class DataMerger {
    weak var mergeDelegate: DataMergeDelegate?

    func mergeData(source1: [String], source2: [String]) {
        let mergedData = source1 + source2
        mergeDelegate?.didMergeData(result: mergedData)
    }
}

class ViewController: UIViewController, DataMergeDelegate {
    func didMergeData(result: [String]) {
        // 統合されたデータを使用する処理
        print(result)
    }

    func fetchDataAndMerge() {
        let dataFromDB = ["DB1", "DB2"]
        let dataFromAPI = ["API1", "API2"]

        let merger = DataMerger()
        merger.mergeDelegate = self
        merger.mergeData(source1: dataFromDB, source2: dataFromAPI)
    }
}