检查 UIAlertController 是否已经呈现的最佳方法是什么？

Question

我有一个表视图，当加载时，每个单元格可能 return 一个 NSError，我选择在 UIAlertController 中显示它。问题是，如果 returned.

有多个错误，我会在控制台中收到此错误

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

理想情况下，我希望在我的 UIAlertController 扩展方法中处理这个问题。

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
}

根据 matt 的回答，我将扩展更改为 UIViewController 扩展，它更简洁并节省了大量 presentViewController 代码。

    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)
    }
}

Answer 1

"already presenting" 不是 UIAlertController，而是 MessagesMasterVC。一个视图控制器一次只能呈现另一个视图控制器。因此出现错误消息。

换句话说，如果您已经告诉视图控制器presentViewController:...，您不能再这样做，直到呈现的视图控制器被关闭。

您可以通过检查 presentedViewController 来询问 MessagesMasterVC 是否已经在呈现视图控制器。如果不是 nil，请不要告诉它 presentViewController:... - 它已经在呈现一个视图控制器。

Answer 2

if ([self.navigationController.visibleViewController isKindOfClass:[UIAlertController class]]) {

      // UIAlertController is presenting.Here

}

Answer 3

嗯，从我的角度来看，上面建议的解决方案有一个本质问题：

如果你问你的ViewController，属性'presentedViewController'是否为nil，答案是false，你不能得出结论，你的UIAlertController已经呈现了。它可以是任何呈现的 ViewController，例如弹出窗口。所以我的建议是一定要检查，警报是否已经在屏幕上如下（将呈现的 ViewController 转换为 UIAlertController）：

if self.presentedViewController == nil {
   // do your presentation of the UIAlertController
   // ...
} else {
   // either the Alert is already presented, or any other view controller
   // is active (e.g. a PopOver)
   // ...

   let thePresentedVC : UIViewController? = self.presentedViewController as UIViewController?

   if thePresentedVC != nil {
      if let thePresentedVCAsAlertController : UIAlertController = thePresentedVC as? UIAlertController {
         // nothing to do , AlertController already active
         // ...
         print("Alert not necessary, already on the screen !")

      } else {
         // there is another ViewController presented
         // but it is not an UIAlertController, so do 
         // your UIAlertController-Presentation with 
         // this (presented) ViewController
         // ...
         thePresentedVC!.presentViewController(...)

         print("Alert comes up via another presented VC, e.g. a PopOver")
      }
  }

}

Answer 4

这个类别可以自动管理所有模态控制器，包括 UIAlertController。

UIViewController+JCPresentQueue.h

Answer 5

只需关闭当前控制器并显示您想要的控制器即

self.dismiss(animated: false, completion: nil)

self.displayAlertController()

Answer 6

这是我在 Swift 中使用的解决方案 3. 这是一个向用户显示警报的函数，如果在用户关闭警报之前多次调用它，它将添加新的已显示的警报的警报文本。如果正在显示其他视图，则不会出现警报。并非所有人都会同意这种行为，但它适用于简单的情况。

extension UIViewController {
    func showAlert(_ msg: String, title: String = "") {
        if let currentAlert = self.presentedViewController as? UIAlertController {
            currentAlert.message = (currentAlert.message ?? "") + "\n\nUpdate:\(title): \(msg)"
            return
        }

        // create the alert
        let alert = UIAlertController(title: title, message: msg, preferredStyle: UIAlertControllerStyle.alert)
        alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))

        // show the alert
        self.present(alert, animated: true, completion: nil)
    }
}

Answer 7

我们可以简单地检查是否显示了任何视图控制器。

如果出现，则检查它是否属于 UIAlertController 类型。

    id alert = self.presentedViewController;

    if (alert && [alert isKindOfClass:[UIAlertController class]]) 
      {
           *// YES UIAlertController is already presented*
      }
    else
       {
        // UIAlertController is not presented OR visible.
       }

Answer 8

我用它来检测、删除和提醒。

首先我们使用以下函数创建一个警报。

 var yourAlert :UIAlertController!

 func useYouAlert (header: String, info:String){


    yourAlert = UIAlertController(title:header as String, message: info as String, preferredStyle: UIAlertControllerStyle.alert)



    let okAction = UIAlertAction(title: self.langText[62]as String, style: UIAlertActionStyle.default) { (result : UIAlertAction) -> Void in
        print("OK") 

    }


    yourAlert.addAction(okAction)
    self.present(yourAlert.addAction, animated: true, completion: nil)

}

在您代码的其他部分

    if yourAlert != nil {

      yourAlert.dismiss(animated: true, completion: nil)

    }

Answer 9

对于最新的 Swift 语言，您可以使用以下语言：

var alert = presentedViewController

if alert != nil && (alert is UIAlertController) {
    // YES UIAlertController is already presented*
} else {
    // UIAlertController is not presented OR visible.
}

Answer 10

Swift 4.2+ Answer

if UIApplication.topViewController()!.isKind(of: UIAlertController.self) { 
            print("UIAlertController is presented")}

对于那些不知道如何获得最顶级的人Viewcontroller

extension UIApplication {


public class func topViewController(_ base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
    if let nav = base as? UINavigationController {
        return topViewController(nav.visibleViewController)
    }
    if let tab = base as? UITabBarController {
        if let selected = tab.selectedViewController {
            return topViewController(selected)
        }
    }
    if let presented = base?.presentedViewController {
        return topViewController(presented)
    }
    return base
}}

Swift 5+ Answer 'keyWindow' was deprecated in iOS 13.0 suggested edit

if UIApplication.topViewController()!.isKind(of: UIAlertController.self) { 
            print("UIAlertController is presented")}

对于那些不知道如何获得最顶级的人Viewcontroller

extension UIApplication {


public class func topViewController(_ base: UIViewController? = UIApplication.shared.windows.first?.rootViewController) -> UIViewController? {
    if let nav = base as? UINavigationController {
        return topViewController(nav.visibleViewController)
    }
    if let tab = base as? UITabBarController {
        if let selected = tab.selectedViewController {
            return topViewController(selected)
        }
    }
    if let presented = base?.presentedViewController {
        return topViewController(presented)
    }
    return base
}}

Answer 11

关闭当前控制器并像

一样呈现警报控制器

 func alert(_ message:String) {
  let alert = UIAlertController(title: "Error!", message: message, preferredStyle: .alert)
  alert.addAction(UIAlertAction(title: "Dismiss", style: .default, handler: nil))
  self.dismiss(animated: false, completion: nil)
  self.present(alert, animated: true,completion: nil)
    }

Answer 12

您可以在一行中测试是否已显示警报：

if self.presentedViewController as? UIAlertController != nil {
    print ("alert already presented")
}

Answer 13

我发现我需要创建一个队列来堆叠 UIAlertController 请求。

NSMutableArray *errorMessagesToShow; // in @interface
errorMessagesToShow=[[NSMutableArray alloc] init];  // in init

-(void)showError:(NSString *)theErrorMessage{
    if(theErrorMessage.length>0){
        [errorMessagesToShow addObject:theErrorMessage];
        [self showError1];
    }
}
-(void)showError1{
    NSString *theErrorMessage;
    if([errorMessagesToShow count]==0)return; // queue finished

    UIViewController* parentController =[[UIApplication sharedApplication]keyWindow].rootViewController;
    while( parentController.presentedViewController &&
      parentController != parentController.presentedViewController ){
        parentController = parentController.presentedViewController;
    }
    if([parentController isKindOfClass:[UIAlertController class]])return;  // busy

    // construct the alert using [errorMessagesToShow objectAtIndex:0]
    //  add to each UIAlertAction completionHandler [self showError1];
    //   then

    [errorMessagesToShow removeObjectAtIndex:0];
    [parentController presentViewController:alert animated:YES completion:nil]; 
}

检查 UIAlertController 是否已经呈现的最佳方法是什么？

What is the best way to check if a UIAlertController is already presenting?

ios

uialertcontroller