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 console if multiple errors are returned.

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

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
}

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)
    }
}

Answer 1

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.