Same optional value is sometimes nil and sometimes not

Question

I have the following in my viewDidAppear:

override func viewDidAppear(_ animated: Bool) {
        // Get the index based off of which tableview cell was selected in the last VC
        let selectedRecipeIndex = recipe.firstIndex(where: {$0.docID == passedDocID})

        // Get the appropriate data based off of the index determined above
        let currentRecipe = recipe[selectedRecipeIndex!]
        titleLabel.text = currentRecipe.title
    }

I'll sometimes get the following error on selectedRecipeIndex!: Fatal error: Unexpectedly found nil while unwrapping an Optional value.

This error is very inconsistent. For the same index/cell, it will return a value but then if I open the app a separate time and tap the same index/cell it might return nil. It's seemingly random.

Why could the same index/cell sometimes return the value but sometimes return nil? And if it returns nil, what can I do to keep trying to call the value until it is not nil?

Crash means that this array has no such element. You only can solve this by yourself using debugging. Add logs to see the content of the recipe before taking first index. — Phil Dukhov
– Phil Dukhov, Commented Sep 4, 2021 at 17:33
Are you getting the recipes through some asynchronous call perhaps? Either way you should use if let… instead of force unwrapping — Joakim Danielson
– Joakim Danielson, Commented Sep 4, 2021 at 17:35
Unrelated - it's best practice to call super.ViewDidAppear(animated) before doing anything in the method — pietrorea
– pietrorea, Commented Sep 4, 2021 at 17:42
Why pass the document id anyway if you are jus going to search for it? Why not pass the recipe itself? — Paulw11
– Paulw11, Commented Sep 4, 2021 at 21:05
It's your job to tell us how this can be. Your code refers to an unknown: recipe. Until you tell us how that is populated and why you are so certain that it contains an element whose docID is passedDocID (and what that is and how it gets populated), this is all just hand-waving. — matt
– matt, Commented Sep 4, 2021 at 23:44

Dharman · Accepted Answer · 2021-09-04 17:51:48Z

-1

Try something like this:

override func viewDidAppear(_ animated: Bool) {
   super.viewDidAppear(animated)
   guard let selectedRecipeIndex = recipe.firstIndex(where: {$0.docID == passedDocID}) else {
       debugPrint("No index found.") // Add your own error handling
       return
   }
   let currentRecipe = recipe[selectedRecipeIndex]
   titleLabel.text = currentRecipe.title
}

You were crashing at the selectedRecipeIndex!, which you can fix with a guard-let or if-let. If there's a situation where there's an index, but it doesn't match up to the size of the recipe array, you can also add separate handling for that so you don't crash there.

edited Sep 4, 2021 at 17:51

Dharman♦

33.9k27 gold badges106 silver badges157 bronze badges

answered Sep 4, 2021 at 17:46

pietrorea

9086 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Joakim Danielson Over a year ago

How can firstIndex return an index that doesn’t exists?

pietrorea Over a year ago

if the array is getting mutated from multiple threads, it might be possible. unlikely though

Collectives™ on Stack Overflow

Same optional value is sometimes nil and sometimes not

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related