Question

生成警报视图时出现此错误“尝试显示其视图不在窗口层次结构中！”。请看下面的代码。我正在使用操作队列来执行警报任务。

class AlertOperation: ASOperation {
    // MARK: Properties

    fileprivate let alertController = UIAlertController(title: nil, message: nil, preferredStyle: .alert)
    fileprivate let presentationContext: UIViewController?

    var title: String? {
        get {
            return alertController.title
        }

        set {
            alertController.title = newValue
            name = newValue
        }
    }

    var message: String? {
        get {
            return alertController.message
        }

        set {
            alertController.message = newValue
        }
    }    

    // MARK: Initialization
    init(presentationContext: UIViewController? = nil) {
        self.presentationContext = presentationContext ?? UIApplication.shared.keyWindow?.rootViewController

        super.init()

        addCondition(AlertPresentation())
        /*
            This operation modifies the view controller hierarchy.
            Doing this while other such operations are executing can lead to
            inconsistencies in UIKit. So, let's make them mutally exclusive.
        */
        addCondition(MutuallyExclusive<UIViewController>())
    }

    func addAction(_ title: String, style: UIAlertActionStyle = .default, handler: @escaping (AlertOperation) -> Void = { _ in }) {
        let action = UIAlertAction(title: title, style: style) { [weak self] _ in
            if let strongSelf = self {
                handler(strongSelf)
            }
            self?.finish()
        }

        alertController.addAction(action)
    }

    override func execute() {
        guard let presentationContext = presentationContext else {
            finish()
            return
        }

        DispatchQueue.main.async {
            if self.alertController.actions.isEmpty {
                self.addAction("OK")
            }
            presentationContext.present(self.alertController, animated: true, completion: nil)
        }
    }
}

这是第一次工作正常，但如果我按警告上的取消按钮比它给我上面的错误。目前，如果用户按下取消按钮，我将从同一功能打开另一个警报。

    final func finish(_ errors: [NSError] = []) {
    if !hasFinishedAlready {
        hasFinishedAlready = true
        state = .finishing

        let combinedErrors = _internalErrors + errors
        finished(combinedErrors)

        for observer in observers {
            observer.operationDidFinish(self, errors: combinedErrors)
        }

        state = .finished
    }
}

Answer 1

检查presentationContext是否存在问题，即窗口层次结构中是否存在其视图，

为此尝试替换

presentationContext.present(self.alertController, animated: true, completion: nil)

带

UIApplication.shared.keyWindow?.rootViewController?.present(self.alertController, animated: true, completion: nil)

如果能够在window's rootViewController上展示，请尝试解析presentationContext。

生成alertview时，UIAlertController会出错

1 个答案: