Displaying a UIAlert before dismissing the view

Question

My view is being dismissed through the previous button on the navigation bar. I think the correct term for that is that the view is being popped off the view stack. Now before actually dismissing the view I want to display a UIAlert asking the user to setup his/her address.

I've tried this but the UIAlert is not being show:

override func viewWillDisappear(animated: Bool) {
    if let currentUser = ApiManager.sharedInstance.currentUser {
        if !currentUser.hasAddress {
            let alert = UIAlertController(title: "Missing address", message: "We see you're stilling missing an address, would you like set it now?", preferredStyle: UIAlertControllerStyle.Alert)

            alert.addAction(UIAlertAction(title: "yes".localized, style: .Default, handler: { (alertAction) in
                let newViewController = LocationViewController()
                newViewController.delegate = self
                self.navigationController?.pushViewController(newViewController, animated: true)
            }))

            alert.addAction(UIAlertAction(title: "no".localized, style: .Default, handler: nil))

            self.presentViewController(alert, animated: true, completion: nil)
        }
    }
}

In my console the following gets printed:

2016-10-28 16:58:47.380 gaifong[17096:14515422] Warning: Attempt to present <UIAlertController: 0x7fd7037e4cb0> on <gaifong.ProfileViewController: 0x7fd7048cc000> whose view is not in the window hierarchy!

Answer 1

You should add leftBarButtonItem on navigationItem and make an action to leftBarButtonItem where you can handle this.

in viewDidLoad

self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: image, style: UIBarButtonItemStyle.Plain, target: self, action: #selector(self.goBack))

// Then handle the button selection
func goBack() {
  if let currentUser = ApiManager.sharedInstance.currentUser {
    if !currentUser.hasAddress {
        let alert = UIAlertController(title: "Missing address", message: "We see you're stilling missing an address, would you like set it now?", preferredStyle: UIAlertControllerStyle.Alert)

        alert.addAction(UIAlertAction(title: "yes".localized, style: .Default, handler: { (alertAction) in
            // here you can pop to main controller
            self.navigationController?.popViewControllerAnimated(true)
        }))

        alert.addAction(UIAlertAction(title: "no".localized, style: .Default, handler: nil))

        self.presentViewController(alert, animated: true, completion: nil)
    }
}
}