检查UIAlertController是否已经显示的最佳方法是什么? [英] What is the best way to check if a UIAlertController is already presenting?

问题描述

我有一个表格视图，该表格视图在加载时可能会返回一个NSError，我已选择将其显示在UIAlertController中.问题是，如果返回多个错误，我会在控制台中收到此错误.

I have a tableview which, when loaded, each cell could possibly return an NSError, which I have chosen to display in a UIAlertController. Problem is I get this error in the console if multiple errors are returned.

警告:尝试在已显示的MessagesMasterVC:0x14e53d800上呈现UIAlertController:0x14e64cb00

Warning: Attempt to present UIAlertController: 0x14e64cb00 on MessagesMasterVC: 0x14e53d800 which is already presenting (null)

理想情况下，理想情况下，我想在UIAlertController扩展方法中处理此问题.

Ideally, I would ideally like to handle this in my UIAlertController extension method.

class func simpleAlertWithMessage(message: String!) -> UIAlertController {

    let alertController = UIAlertController(title: nil, message: message, preferredStyle: UIAlertControllerStyle.Alert)
    let cancel = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)

    alertController.addAction(cancel)
    return alertController
}

基于matt的回答，我将扩展名更改为UIViewController扩展名，它更加简洁，并节省了许多presentViewController代码.

Based on matt's answer, I changed the extension to a UIViewController extension, its much cleaner and saves lots of presentViewController code.

    func showSimpleAlertWithMessage(message: String!) {

    let alertController = UIAlertController(title: nil, message: message, preferredStyle: UIAlertControllerStyle.Alert)
    let cancel = UIAlertAction(title: "Ok", style: .Cancel, handler: nil)

    alertController.addAction(cancel)

    if self.presentedViewController == nil {
        self.presentViewController(alertController, animated: true, completion: nil)
    }
}

推荐答案

不是UIAlertController在已经呈现"，而是MessagesMasterVC.一个视图控制器一次只能显示一个其他视图控制器.因此出现错误消息.

It is not the UIAlertController that is "already presenting", it is MessagesMasterVC. A view controller can only present one other view controller at a time. Hence the error message.

换句话说，如果您已将视图控制器告知presentViewController:...，则在关闭所提供的视图控制器之前，您将无法再次执行该操作.

In other words, if you have told a view controller to presentViewController:..., you cannot do that again until the presented view controller has been dismissed.

您可以通过检查其presentedViewController来询问MessagesMasterVC是否已经在提供视图控制器.如果不是nil，请不要告诉它presentViewController:...-它已经在提供视图控制器.

You can ask the MessagesMasterVC whether it is already presenting a view controller by examining its presentedViewController. If not nil, do not tell it to presentViewController:... - it is already presenting a view controller.

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