尝试显示带有消息的 UIAlertController 时应用程序崩溃：由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'

Question

此警报控制器已初始化：

let alertVC2 = PMAlertController(title: "Need to always enable location authorization", description: "Go to Settings -> App -> Location. Then select 'Always'.", image: UIImage(named: "Location"), style: .alert)

在 ViewDidLoad() 中，动作被添加到 alertVC2。

alertVC2.addAction(PMAlertAction(title: "OK", style: .default, action: { () in

            print("Capture action OK")
            self.alertVC2.dismiss(animated: true, completion: nil)
        }))

 alertVC2.addTextField { (textField) in
            textField?.placeholder = "Location..."
        }

此外，在 viewDidLoad() 中添加了这段代码，这将允许我运行调用 willResignActive 的函数，当应用程序在后台保持休眠状态后再次激活时:

 NotificationCenter.default.addObserver(self, selector: #selector(willResignActive), name: UIApplication.didBecomeActiveNotification, object: nil)

这是一个函数，当应用再次激活时运行s:

@objc func willResignActive(_ notification: Notification) {
        print("activated")

      check()
    }

在check() 函数中，将调用alertVC2 (AlertController) 并将警报控制器显示在屏幕上。当我通过将应用程序恢复运行使其恢复生机时，将显示 alertcontroller。但是，当我第二次退出应用程序并再次return时，它不会显示alertVC2。当我第三次这样做时，应用程序崩溃了。

下面是 check() 函数的简要介绍：

func check() {

    if CLLocationManager.authorizationStatus() == .notDetermined || CLLocationManager.authorizationStatus() == .authorizedWhenInUse || CLLocationManager.authorizationStatus() == .denied || CLLocationManager.authorizationStatus() == .restricted {

    locationManager.requestWhenInUseAuthorization()
        locationManager.requestAlwaysAuthorization()

        if CLLocationManager.authorizationStatus() != .authorizedAlways {

        print("Need to always authorize location for me")

        self.present(alertVC2, animated: true, completion: nil)

        }
    }

    if CLLocationManager.authorizationStatus() == .authorizedAlways {

        locationManager.startUpdatingLocation()

    }


}

这是我在第三次尝试时应用程序崩溃时收到的错误消息：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present modally an active controller

我该怎么做才能避免崩溃并继续 post alertcontroller？

Answer 1

听起来您正试图多次显示警报控制器。如果在你调用self.present的那一行打断点，它命中了多少次？

如果我猜对了，这里的简单方法是检查视图当前是否正在显示任何内容，如果是，则跳过显示您的警报。也许是这样的：

if CLLocationManager.authorizationStatus() != .authorizedAlways {
    print("Need to always authorize location for me")
    if self.presentedViewController == nil {
        self.present(alertVC2, animated: true, completion: nil)
    }

}

或者类似的东西：

if CLLocationManager.authorizationStatus() != .authorizedAlways {
    print("Need to always authorize location for me")
    if !alertVC2.isBeingPresented { // make sure we're not already presenting this alert to the user
        self.present(alertVC2, animated: true, completion: nil)
    }

}

尝试显示带有消息的 UIAlertController 时应用程序崩溃：由于未捕获的异常而终止应用程序 'NSInvalidArgumentException'

App crashes when attempting to display UIAlertController with message: Terminating app due to uncaught exception 'NSInvalidArgumentException'

ios

swift

uialertcontroller

swift4