swift - 如何在 UIViewController 之间使用委托(delegate)？

Question

我已经搜索过了:

• Passing Data between View Controllers
• Passing data between two ViewControllers (delegate) - Swift
• Reload collection view data from another view class

但找不到答案。基本上我有两个 View Controller ，并尝试使用委托(delegate)来更新数组并最终重新加载 Collection View 。

ViewController1

    class ViewController1: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, AppendDelegate {

    let cellID = "cell"

    var list = ["item1", "item2", "item3"]
    let otherView = ViewController2()

    override func viewDidLoad() {
        super.viewDidLoad()

        otherView.delegate = self
        print(list)

        let collection = UICollectionView(frame: view.bounds)
        collection.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellID)
        collection.delegate = self
        collection.dataSource = self
        collection.backgroundColor = UIColor.cyan

        view.backgroundColor = .white
        view.addSubview(collection)

        self.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .action, target: self, action: #selector(moveToOtherVC))
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellID, for: indexPath) as UICollectionViewCell
        cell.backgroundColor = UIColor.black
        return cell
    }

    func appendItem(string: String) {
        list.append(string)
        print(list)
    }

    @objc func moveToOtherVC() {
        let VC2 = UINavigationController(rootViewController: ViewController2())
        present(VC2, animated: true, completion: nil)
    }
}

我的第二个 View Controller

    protocol AppendDelegate {
    func appendItem(string: String)
}

class ViewController2: UIViewController {

    var delegate: AppendDelegate?

    let textField: UITextField = {
        let tf = UITextField(frame: CGRect(x: 0, y: 0, width: 39, height: 20))
        tf.backgroundColor = .blue
        return tf
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        view.addSubview(textField)

        self.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .action, target: self, action: #selector(sendDataToCollection))

        textField.center.x = view.center.x
        textField.center.y = view.center.y
    }

    @objc func sendDataToCollection() {
        guard let text = textField.text else {return}
        self.delegate?.appendItem(string: text)
        textField.text = ""
        moveToVC()
    }

    @objc func moveToVC() {
        dismiss(animated: true, completion: nil)
    }

}

在第二个类中， self.delegate.appendItem 不应该导致 ViewController1 追加到列表中吗？

我还使用通知中心作为委托(delegate)的替代方案，但没有成功。

Answer 1

您几乎所做的一切都是正确的，但是您将 ViewController2 的委托(delegate)设置错误。

您实际上是在 viewDidLoad 中设置 ViewController2 新实例的委托(delegate)，但在 moveToOtherVC 中您呈现了不同的 ViewController2 作为 UINavigationController

的根

而是设置ViewController2新实例的委托(delegate)，并使用该实例作为呈现navigationController的rootViewController

@objc func moveToOtherVC() {
    let vc2 = ViewController2()
    vc2.delegate = self
    let navigationController = UINavigationController(rootViewController: vc2)
    present(navigationController, animated: true, completion: nil)
}

或者您只需将 otherView 作为 navigationController 的 rootViewController 传递即可解决您的问题

let navigationController = UINavigationController(rootViewController: otherView)