Constraint items must each be a view or layout guide

Question

I'm trying to add an Admob Banner at the bottom of my UIViewController:

func addBannerViewToView() {
    bannerView = GADBannerView(adSize: kGADAdSizeBanner)
    bannerView.adUnitID = "ca-app-pub-HIDDEN/HIDDEN"
    bannerView.rootViewController = self
    bannerView.delegate = self
    bannerView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(bannerView)
    view.addConstraints(
        [NSLayoutConstraint(item: bannerView,
                            attribute: .bottom,
                            relatedBy: .equal,
                            toItem: view.safeAreaLayoutGuide.bottomAnchor,
                            attribute: .top,
                            multiplier: 1,
                            constant: 0),
         NSLayoutConstraint(item: bannerView,
                            attribute: .centerX,
                            relatedBy: .equal,
                            toItem: view,
                            attribute: .centerX,
                            multiplier: 1,
                            constant: 0)
        ])
    bannerView.load(GADRequest())
}

I call this function in viewDidLoad but app crashes with:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'NSLayoutConstraint for >: Constraint items must each be a view or layout guide.'

I used an official example https://developers.google.com/admob/ios/banner

Answer 1

The error is in the first constraint. The correct formulation in iOS 12 is:

NSLayoutConstraint(item: bannerView,
                   attribute: .bottom,
                   relatedBy: .equal,
                   toItem: view.safeAreaLayoutGuide,
                   attribute: .bottom,
                   multiplier: 1,
                   constant: 0)

It means that the attribute bottom of the bannerView has to be equal to the bottom attribute of the view.safeAreaLayoutGuide.

Answer 2

Replace

toItem: view.safeAreaLayoutGuide.bottomAnchor,

With

toItem: view.safeAreaLayoutGuide,

Or

toItem: view,

You specify an anchor while as the exception says it must be a usual view or a layoutGuide

Answer 3

This worked:

func addBannerViewToView() {
        bannerView = GADBannerView(adSize: kGADAdSizeBanner)
        bannerView.adUnitID = "ca-app-pub-HIDDEN/HIDDEN"
        bannerView.rootViewController = self
        bannerView.delegate = self
        bannerView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(bannerView)
        view.addConstraints(
            [NSLayoutConstraint(item: bannerView,
                                attribute: .bottom,
                                relatedBy: .equal,
                                toItem: view,
                                attribute: .bottomMargin,
                                multiplier: 1,
                                constant: 0),
             NSLayoutConstraint(item: bannerView,
                                attribute: .centerX,
                                relatedBy: .equal,
                                toItem: view,
                                attribute: .centerX,
                                multiplier: 1,
                                constant: 0)
            ])
        bannerView.load(GADRequest())
    }