I think you have to use systemName toggleShowSaveCatDescript.setImage(UIImage(systemName: "questionmark.circle.fill"), for: .normal)

Look at this: class ViewController: UIViewController, UITextFieldDelegate { @IBOutlet weak var weightInput: UITextField! @IBOutlet weak var heightInput: UITextField! @IBOutlet weak var BMIOutput: UITextField! @IBOutlet weak var categoryOutput: UILabel! override func viewDidLoad() { super.viewDidLoad() // Do any additional setup after loading the view, typically from a nib. self.weightInput.delegate = self //added either ! or ? here and don't get fatal error self.heightInput.delegate = self //added either ! or ? here and don't get fatal error } Line 2 you declare an IBOutlet, as implicitly unwrap. That means that weightInput is an optional, so either nil or some value. Implicitly unwrap means that if you call it once it has a value, you don't need to unwrap anymore. It is done implicitly. But, if you call when it is not initialized (nil) and try to unwrap, of course you crash. And an IBOutlet is loaded and initialized when the view is loaded. But the IBOulet var is initialized only if it is properly connected to the object in storyboard. Otherwise, no way to know which var to initilize, hence it remains nil. So most likely in your case, the connection between th IBOutlet and the TextField in storyboard is not set or is broken. Then, when you call line 10: self.weightInput.delegate = self Do you see a black dot on the left of @IBOutlet weak var weightInput: UITextField! If not, control drag from the white circle to the textField in storyboad. The connection will be made, and crash will disappear (if you do it for all IBOutlets). Note: you wrote: The code builds in both cases and only produces a Fatal Error when I run the simulator without the unwrapping tags. With the unwrapping added the simulator runs, but when I enter the data and click on the link nothing appears in the MY BMI text box. It is logical not to crash with ?, but a bit surprising you do not crash with ! If weightInput is nil, when you set with optional chaining self.weightInput?.delegate = self in fact it does nothing (execution "halted" after ? because of nil). TextField appear on screen, you can type, but delegate functions (as textFieldShouldReturn) are not called. Nothing appears in the MY BMI text

What do you want in order ? pickedCat == 1 before 2, before 3 and before 4 ? If so, the only thing that matters is how you set pickedCat. But you don't show this part of code…

I need the function to run before it sets the text. Which function ? You don't show anything about it. How do you want anyone to guess ? Please, explain properly what you need and provide relevant information, otherwise, it is impossible to help.

IMHO having several cell prototypes is a good way to go. The only point is reloading the complete table. Why not just reload some cells ?

If I understand your question correctly. You have 2 things : the data for all the information you save in Core Data the status of some as favorite. This may be stored in the core data or simpler in suerSettings (with a reference to the data ID)

You mean. Sure. But this func shows nowhere in the code you posted. Is it that confidential that you cannot show useful code to help you ?

Thanks for showing. However, I do not understand how this relates to your initial post. And what is it you want to have in a specific order.

That's not totally clear… without pushing my initial viewcontroller? What do you mean ? What is the problem with push ? Did you consider using a modal segue for instance of a popover ? Or embedding your first VC in a navigation controller ?

As you are new to the forum, I remind you that you should close the thread if the answer is OK for you, by marking the correct answer. Wish you good learning.

I would be very surprised if that were possible. Think of it: that would mean that your app would know what user is buying. And could make any use of this information. That would be a disastrous privacy breach. So, I would advise to forget it and design an easy to use way for user to enter this information himself or herself in your app.

First thing to check is whether or not currentFrResponse.remarks is nil. A simple way to do this is to comment out line 7. If the app crashes, that means it was nil.

Did you do an option-clean Build folder ? You ought to. What do you see exactly and completely in Attributes inspector when you select 1024 icon in XCassets AppIcon ? Please describe for all fields.

I have also checked the debugger and it shows a the string present present where ? In currentFrResponse.remarks! ?

Yes it is, but not this way. You need to convert first to String, then append then convert back to Double. Such as: var num: Double = 1 let numString = String(num) let numStrPlus = "1" + numString var num2 = Double(numStrPlus)! // num.append(1) print(num2) You can have a more condensed form: var num: Double = 1 var num2 = Double("1" + String(num)) ?? 0 or var num2 = Double(String(1) + String(num)) ?? 0 If you really want to write it as append, you can define an extension to Double: extension Double { func append(_ val: Int) - Double { return Double(String(val) + String(self)) ?? 0 } } num2 = num.append(1)