Question

我为UIAlertViewController声明了一个全局变量，以便能够在类内部的不同方法中显示和关闭它。我显示了两种警报：首先，带有按钮的警报，当遇到错误时将显示该按钮或显示一条信息消息。第二个是没有按钮的警报，它将像进度消息一样显示。

这是示例代码：

private var alert: UIAlertController? // global declaration

private func showProgressMessage(sender viewController: UIViewController, message alertMessage: String)
{
    DispatchQueue.main.async
    {
        self.alert= UIAlertController(title: "", message: alertMessage, preferredStyle: .alert)
        viewController.present(self.alert!, animated: true, completion: nil)
    }
}

private func showAlertMessage(sender viewController: UIViewController, title alertTitle: String, message alertMessage: String)
{
    DispatchQueue.main.async
    {
        self.alert= UIAlertController(title: alertTitle, message: alertMessage, preferredStyle: .alert)

        self.alert!.addAction(UIAlertAction(title: "OK", style: .default, handler: nil))
        viewController.present(self.alert!, animated: true, completion: nil)
    }
}

private func method1()
{
    DispatchQueue.global().async
    {
        // some code here
        self.showProgressMessage(sender: self, message:  "Processing...")
        // some code here
    }
}

private func method2()
{
    // some code here
    self.alert!.dismiss(animated: false)
    {
        self.showAlertMessage(sender: self, message:  "Done")
    }

    self.displayOtherViewController()
}

private func displayOtherViewController()
{
    self.alert?.dismiss(animated: false)
    {
        if let viewController = self.storyboard?.instantiateViewController(withIdentifier: "Sample")
        {
            let view = viewController as! SampleViewController

            view .modalTransitionStyle = .crossDissolve

            self.present(view , animated: true, completion: nil)
        }
    }
}

在method2中，与视图控制器相同，再次显示警报将需要几秒钟的时间才能显示。在Swift 4中显示和分发UIAlertController的正确方法是什么？

Answer 1

似乎您的代码是从后台线程启动的。 即使是关闭也必须在主线程上调用 试试这个：

private func method2() {
    DispatchQueue.main.async {
        self.alert!.dismiss(animated: false) {
            self.showAlertMessage(sender: self, message:  "Done")
        }
        self.displayOtherViewController()
    }
}

在Swift 4中显示和删除UIAlertController

1 个答案: