ios - 如何从委托(delegate)方法启动 UIAlertController？

我的代码非常基础。我有 2 个 View Controller 。在名为“FirstScreen”的第一个 viewController 上有一个按钮，通过模态 segue 将我带到第二个屏幕，那里还有一个按钮。 “SecondScreen”有一个带有 1 方法的协议(protocol)，“FirstScreen”符合该协议(protocol)。所以基本上我试图从该方法调用 UIAlertController，同时按下“SecondScreen”的按钮。结果我得到:

"Warning: Attempt to present.....on....whose view is not in the window hierarchy!

我知道我可以在我的 Storyboard 中嵌入一个导航 Controller 并且警报会起作用，但对我来说不是这样。我也想以这种方式调用警报，因为需要知道 CLAuthorizationStatus。

So maybe is there any way of getting the status directly from the "SecondScreen" ?

import UIKit
import CoreLocation

class FirstScreen: UIViewController {

    @IBAction func firstTapped(_ sender: UIButton) {
        let selectionVC = storyboard?.instantiateViewController(withIdentifier: "secondVC") as! SecondScreen
        present(selectionVC, animated: true, completion: nil)
        selectionVC.delegate = self
    }
}

extension FirstScreen: LocationPermissionDelegate {

    func checkLocationStatus() {

        let status = CLLocationManager.authorizationStatus()
        if status == CLAuthorizationStatus.notDetermined {

            let alert = UIAlertController(title: "Just a message", message: "HEYYY!", preferredStyle: .alert)
            let action = UIAlertAction(title: "Dismiss", style: .default, handler: nil)
            alert.addAction(action)
            present(alert, animated: true)
        }
    }
}

import Foundation
import UIKit

protocol LocationPermissionDelegate {
    func checkLocationStatus()
}

class SecondScreen: UIViewController {

    var delegate: LocationPermissionDelegate?

    @IBAction func secondTapped(_ sender: UIButton) {

        delegate?.checkLocationStatus()  
    }
}

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Best Answer-推荐答案

firstvc目前正在展示

present(selectionVC, animated: true, completion: nil)

所以你不能在这里显示警报

present(alert, animated: true)

移动这个

func checkLocationStatus() {

    let status = CLLocationManager.authorizationStatus()
    if status == CLAuthorizationStatus.notDetermined {

        let alert = UIAlertController(title: "Just a message", message: "HEYYY!", preferredStyle: .alert)
        let action = UIAlertAction(title: "Dismiss", style: .default, handler: nil)
        alert.addAction(action)
        present(alert, animated: true)
    }
}

到第二个vc，在那里做演示

关于ios - 如何从委托(delegate)方法启动 UIAlertController？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54275477/