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

Question

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

Answer 1

For latest Swift language you can use following:

var alert = presentedViewController

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

Answer 2

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

      // UIAlertController is presenting.Here

}

Answer 3

I found I needed to create a queue to stack the UIAlertController requests.

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]; 
}

Answer 4

Swift 4.2+ Answer

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

For those who don't know how to get top most 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")}

For those who don't know how to get top most 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 5

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.

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.

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.

Answer 6

I used that to detect and remove and alert.

First we create an alert with following function.

 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)

}

And in some other part of your code

    if yourAlert != nil {

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

    }