应用启动时显示UIAlertView

Question

我正在尝试在应用程序首次加载时添加UIAlertView或Controller.目前,我的方法中有这个代码viewDidLoad.

let welcomeAlert = UIAlertController(title: "hola", message: "this is a test.", preferredStyle: UIAlertControllerStyle.Alert)
welcomeAlert.addAction(UIAlertAction(title: "ok.", style: UIAlertActionStyle.Default, handler: nil))

self.presentViewController(welcomeAlert, animated: true, completion: nil)

为什么不显示警报视图？我使用相同的代码,但在IBAction一个按钮内,它按预期工作.

Answer 1

您应该在viewDidAppear:功能中显示警报.要显示子视图或其他视图控制器,父视图控制器必须位于视图层次结构中.

该viewDidAppear功能"通知视图控制器其视图已添加到视图层次结构中".

_{*来自文档}

所以,你的代码看起来像这样:

class MyViewController: UIViewController {

    override func viewDidAppear(animated: Bool){
        super.viewDidAppear(animated)

        let welcomeAlert = UIAlertController(title: "hola", message: "this is a test.", preferredStyle: UIAlertControllerStyle.Alert)
        welcomeAlert.addAction(UIAlertAction(title: "ok.", style: UIAlertActionStyle.Default, handler: nil))
        self.presentViewController(welcomeAlert, animated: true, completion: nil)
    }

}