ios - Calling function from child view controller not working

Question

Hi I have a parent view controller with a mapView and a child view controller within it, as a small container view on the bottom, and that container view is normally hidden. When I tap on a marker on the mapView from the parent view controller, I want to show that container view and change the labels on the child view controller to values I get from a database.

Right now, what I have here is me calling the function from the parent view controller (when the marker is tapped) to change the labels on the child view controller.

in my parent view controller:

 func mapView(_ mapView: GMSMapView, didTap marker: GMSMarker) -> Bool {
        
        
        
        AddressViewController.ID.selectedID = marker.snippet ?? ""
        
        
        UIView.transition(with: AddressView, duration: 1, options: .transitionFlipFromBottom, animations: {self.AddressView.isHidden = false}, completion: nil)
    
        let AddressViewController = AddressViewController()
        AddressViewController.loadAddressView()
        
        
        let camera = GMSCameraPosition.camera(withTarget: marker.position, zoom: 16)
        mapView.animate(to: camera)

        return true
    }

in AddressViewController (the child view controller)

func loadAddressView() {
        
        if ID.selectedID == "" {
            print("ID did not pass")
            return
        }
        else {
            print("function worked")
            
            ref = Database.database().reference().child("Items").child(ID.selectedID)
            ref?.observeSingleEvent(of: .value, with: {(snapshot) in
                
                let value = snapshot.value as? NSDictionary  
            
                self.ItemNameLabel.text = value?["ItemName"] as? String ?? ""
                self.addressLabel.text = value?["AddressDisplay"] as? String ?? ""

            })
            
        }
    }

What is happening is that when I run it and press the marker, it crashes, and it tells me that ItemNameLabel is "unexpectedly found nil while unwrapping an optional value." However, I could tell the function still was called because "function worked" (above) was still printed, only the label was found nil. So I tried things such as using a delegate and protocol to call the function, which, while it didn't crash, the delegate was never called for some reason (I might of been doing it wrong- if that is how to solve to problem, I would love it if someone please explain how to do it in my case). I also tried setting my label to the database data in the viewDidLoad of the child view controller, and calling the child view controller's loadView() from the parent view controller, and that didn't crash, but didn't change the label either.

Anyone have an idea on how to fix this? Thanks in advance.

question from:https://stackoverflow.com/questions/65938673/calling-function-from-child-view-controller-not-working

Answer 1

You are initiating a view controller as if it was a regular model class. This will initiate the view controller, but you do not instantiate the view controller to appear in your storyboard. For this reason your view life cycle is not used and the item label will not be initiated and is therefore nil.

I will assume that the container view is the only child of your prent view controller. If this is richt, you should instantiate your AddressViewController in your viewDidLoad like this:

let addressViewController = self.childViewControllers.first as! AddressViewController

I assume the Child View Controller is there and can make an explicit unwrapping.

Since you need to hide your container view, you can create an outlet to the parent viewcontroller and when the user clicks on the marker you unhide the container and call the loadAddressView like this:

addressViewController.loadAddressView

Since your AddressViewController is initiated properly all the labels are initialized and will work.

Kind regards, MacUserT