Question

仅当当前UIViewController实现该协议独立于我继承的Base类时，我才希望能够在viewDidLoad上调用协议方法。我正在使用下面的Playground代码来说明当前的位置，它调用了该函数，但由于发生EXC_BAD_ACCESS (code=1, address=0x0).错误而崩溃，仅此而已。

import UIKit

protocol AccessibleProtocol where Self: UIViewController {
    func applyAccessibility()
}

class BaseViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        (self as? AccessibleProtocol)?.applyAccessibility()
    }
}

class LoginViewController: BaseViewController {
    var passwordTextField: UITextField!
    override func viewDidLoad() {
        passwordTextField = UITextField()
        super.viewDidLoad()
    }
}

extension LoginViewController: AccessibleProtocol {
    func applyAccessibility() {
        self.passwordTextField.accessibilityLabel = "Enter Password"
    }
}

let loginViewController = LoginViewController()
loginViewController.viewDidLoad()

Answer 1

您可以做的是使协议（的种类）功能为可选。

import UIKit

protocol AccessibleProtocol where Self: UIViewController {
    func applyAccessibility()
}

extension AccessibleProtocol {
    func applyAccessibility() {}
}

class BaseViewController: UIViewController, AccessibleProtocol {
    override func viewDidLoad() {
        super.viewDidLoad()
        applyAccessibility()
    }
}

class LoginViewController: BaseViewController {
    var passwordTextField: UITextField!
    override func viewDidLoad() {
        passwordTextField = UITextField()
        super.viewDidLoad()
    }
}

extension LoginViewController {
    func applyAccessibility() {
        self.passwordTextField.accessibilityLabel = "Enter Password"
    }
}

let loginViewController = LoginViewController()
loginViewController.viewDidLoad()

这样，您可以始终从协议中调用de func。而且，如果您没有实现它，它什么也不会做。

当ViewController可能实现或未实现协议时，在UIViewController的viewDidLoad上调用协议函数

1 个答案: