Question

为什么这个委托模式不起作用？在DelegateViewController中选择一个Button后，我想在第二个ViewController（标签出口）中显示name属性

我已完成以下步骤：

在＆＃34; Boss＆＃34;中创建协议ViewController - ＆gt; DelegateViewController
将我的功能分配给此协议 - ＆gt; selectedButton
在DelegateViewController中创建selectionButtonDelegate变量
在ViewController中，我创建了一个新的DelegateViewController（）
在viewDidLoad中，我已经分配了实例的委托等于自我
我创建了一个带有传递参数

DelegateViewController：

import UIKit

protocol SelectionDelegate {
    func selectedButton(name: String)
}

class DelegateViewController: UIViewController {
    var selectionButtonDelegate: SelectionDelegate!

    @IBAction func bayernButton(_ sender: UIButton) {
        selectionButtonDelegate.selectedButton(name: "Bayern")
    }

    @IBAction func dortmundButton(_ sender: UIButton) {
        selectionButtonDelegate.selectedButton(name: "Dortmund")

    }
}

的ViewController：

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var selectedButton: UILabel!

    let model = DelegateViewController()

    override func viewDidLoad() {
        super.viewDidLoad()
        model.selectionButtonDelegate = self
    }
}

extension ViewController: SelectionDelegate {
    func selectedButton(name: String) {
        selectedButton.text = name

    }
}

Answer 1

通过查看代码问题，您的实现看起来很不错

let model = DelegateViewController()

您正在创建DelegateViewController的新实例，但您必须从DelegateViewController控制器的其他实例中单击按钮。

您可能需要获取model的正确实例，而不是创建新实例，或者应该从新创建的View Controller实例中点击按钮。

示例：可能需要执行类似

的操作

class ViewController: UIViewController {
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        super.prepare(for: segue, sender: sender)

        if let navigationController = segue.destination as? DelegateViewController {
                selectionButtonDelegate = self = self
        }
     }
}

Answer 2

您没有将selectionButtonDelegate分配给当前活动的DelegateViewController。修改代码以访问DelegateViewController的当前实例。

import UIKit

protocol SelectionDelegate {
    func selectedButton(name: String)
}

class DelegateViewController: UIViewController {

    static weak var shared: DelegateViewController!

    weak var selectionButtonDelegate: SelectionDelegate!

    override func viewDidLoad() {
        super.viewDidLoad()
        DelegateViewController.shared = self
    }

    @IBAction func bayernButton(_ sender: UIButton) {
        selectionButtonDelegate.selectedButton(name: "Bayern")
    }

    @IBAction func dortmundButton(_ sender: UIButton) {
        selectionButtonDelegate.selectedButton(name: "Dortmund")

    }
}




import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var selectedButton: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        DelegateViewController.shared.selectionButtonDelegate = self
    }
}

extension ViewController: SelectionDelegate {
    func selectedButton(name: String) {
        selectedButton.text = name
    }
}

同样在大多数情况下，在Swift中声明委托变量之前使用weak来避免内存泄漏。

Swift 4中的委托模式不起作用！任何人都可以在Swift 4中解释正确的委托模式吗？

2 个答案: