Error when re-presenting view controller - ios

Question

I present a modal view controller in which the user can enter some information, then upon saving that information with this function...
func handleSave() {
guard let newProductUrl = NSURL(string: urlTextField.text!) else {
print("error getting text from product url field")
return
}
guard let newProductName = self.nameTextField.text else {
print("error getting text from product name field")
return
}
guard let newProductImage = self.logoTextField.text else {
print("error getting text from product logo field")
return
}
DispatchQueue.main.async {
self.productController?.save(name: newProductName, url: newProductUrl as URL, image: newProductImage)
}
// Present reloaded view controller with new product added
let ac = UINavigationController()
let pController = ProductController()
productController = pController
ac.viewControllers = [pController]
present(ac, animated: true, completion: nil)
}
... I get an error in the viewWillAppear of ProductController (the controller that presented the modal view controller, and now am trying to get back to)
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
guard let appDelegate =
UIApplication.shared.delegate as? AppDelegate else {
return
}
let managedContext =
appDelegate.persistentContainer.viewContext
let companyToDisplay = self.navigationItem.title!
let fetchRequest =
NSFetchRequest<NSManagedObject>(entityName: "Product")
fetchRequest.predicate = NSPredicate(format:"company.name == %#",companyToDisplay)
do {
products = try managedContext.fetch(fetchRequest)
print(products)
} catch let error as NSError {
print("Could not fetch. \(error), \(error.userInfo)")
}
}
The error is: unexpectedly found nil while unwrapping an optional, on the line let companyToDisplay = self.navigationItem.title!. How do I specify that the self.navigationItem.title that it's looking for (and missing) is the self.navigationItem.title of the controller that sent the modal view?
Thanks for any help, I've been trying to sort this problem out for days and can't figure it out.
EDIT: This is how I present the modal view AddProductController from my ProductController
func presentModalView() {
let nc = UINavigationController()
let addProductController = AddProductController()
nc.viewControllers = [addProductController]
self.modalTransitionStyle = UIModalTransitionStyle.coverVertical
self.modalPresentationStyle = .currentContext
self.present(nc, animated: true, completion: nil)
}
EDIT: Putting code inside dispatch block:
DispatchQueue.main.async {
self.productController?.save(name: newProductName, url: newProductUrl, image: newProductImage)
let pController = ProductController()
self.productController = pController
self.navigationController?.pushViewController(pController, animated: true)
}

Answer 1

The problem is that the block inside this call:
DispatchQueue.main.async {
self.productController?.save(name: newProductName, url: newProductUrl as URL, image: newProductImage)
}
actually executes after your handleSave() method returns. Looks like you're expecting it to execute sequentially with respect to the other code in that method.
DispathQueue.main.async adds a block to a queue of code to be executed at some point in the future -- it doesn't execute immediately.
To fix this, you need to put code inside the dispatch block which does whatever needs to happen next. This would be similar to what you have here:
// Present reloaded view controller with new product added
let ac = UINavigationController()
let pController = ProductController()
productController = pController
ac.viewControllers = [pController]
present(ac, animated: true, completion: nil)
But you probably want to clean up how/where you're creating and dismissing view controllers -- what you have here looks like it will unnecessarily pile up a bunch of view controllers.

Answer 2

Here is your problem, you used present(ac, animated: true, completion: nil) to get to this view, so this presentation is modal and there is no navigationController.
You have to use UINavigationController.pushViewController to present the view and this way you will get the navigationController.
Edit:
let nc = UINavigationController()
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let addProductController = storyboard.instantiateViewController(withIdentifier: "addProductVC")
nc.viewControllers = [addProductController]
self.modalTransitionStyle = UIModalTransitionStyle.coverVertical
self.modalPresentationStyle = .currentContext
self.present(nc, animated: true, completion: nil)
Just don't forget to set the identifier for the addProductController in storyboard, change the storyboard and VC identifier to your ones.
Edit 2 :
let nc = UINavigationController()
let addProductController = ProductController()
addProductController.navigationItem.title = "Have a good one"
nc.viewControllers = [addProductController]
self.modalTransitionStyle = UIModalTransitionStyle.coverVertical
self.modalPresentationStyle = .currentContext
self.present(nc, animated: true, completion: nil)