UIAlertController 代码运行，但不显示警报 [英] UIAlertController code runs, but doesn't present an alert

问题描述

我正在尝试使用 swift 制作应用内弹出式警报，但遇到了一个我一无所知的错误.

I am trying to make an in-app popup alert using swift and I have run into an error that I know nothing about.

这是我用来显示警报的代码:

Here is the code I use to present my alert:

let welcomeAlert = UIAlertController(title: "Welcome!", message: "message here", preferredStyle: UIAlertControllerStyle.Alert)
welcomeAlert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil))
self.presentViewController(welcomeAlert, animated: true, completion: nil)

println("welcome alert displayed!")

我返回的错误是这样的:

The error I'm getting back says this:

Warning: Attempt to present <UIAlertController: 0x7b89a950> on <MyApp.RootClientViewController: 0x7aea8fb0> whose view is not in the window hierarchy!

紧随其后的是打印声明，说明显示欢迎警报！.

This is immediately followed by a printed statements stating welcome alert displayed!.

所以我的代码肯定正在运行，但由于某种原因，它不会显示警报...

So my code is certainly running, but for some reason, it won't display the alert...

我做错了什么?

推荐答案

错误信息告诉你答案:视图不在窗口层次结构中！" 表示 self.view<调用时/code> 不在屏幕上(从技术上讲，这意味着 UIApplication.sharedApplication().keyWindow 不是 self.view 的祖先).

The error message tells you the answer: "view is not in the window hierarchy!" means self.view is not on screen when the call is made (technically it means UIApplication.sharedApplication().keyWindow is not an ancestor of self.view).

通常在 viewDidLoad() 或 viewWillAppear(animated: Bool) 中呈现视图控制器时会发生这种情况.等待 viewDidAppear(animated: Bool)，从 UIApplication.sharedApplication().delegate.window.rootViewController 出现或从 UIApplication.sharedApplication().keyWindow 出现.rootViewController.

Usually this happens when presenting a view controller in viewDidLoad() or viewWillAppear(animated: Bool). Wait for viewDidAppear(animated: Bool), present from UIApplication.sharedApplication().delegate.window.rootViewController or present from UIApplication.sharedApplication().keyWindow.rootViewController.

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