I keep Getting The Error: Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

Question

It says Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

(my code)

func getData()  {

   let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Entity")
    request.returnsObjectsAsFaults = false
    do {
        let result = try? context.fetch(request)

        for data in result as! [NSManagedObject] {

            FacialViewControllerA = data.value(forKey: "titleA") as! String


    }

Possible duplicate of: [What does "Fatal error: Unexpectedly found nil while unwrapping an Optional value" mean?](https://stackoverflow.com/questions/32170456/what-does-fatal-error-unexpectedly-found-nil-while-unwrapping-an-optional-valu) — TylerP, Apr 25 '20 at 19:22
your result is nil and you are trying to force wrap to [NSManagedObject]. That's why this error is coming. — Mohit Kumar, Apr 25 '20 at 19:24

Vikram Parimi · Answer 1 · 2020-04-25T20:13:06.787

2

Please refer to Tyler's comment so you learn more about optionals. Also, avoid the usage of ! which is used to force unwrap objects.

In your case, the crash could be happening due to two reasons:

Either the object you are trying to unwrap is not an array [NSManagedObject]
Or the fetchRequest returned 0 objects or nil value

To avoid the crash you should opt for optional unwrapping which is the safest way of unwrapping an object. You can either a guard-let or If-let statement Please refer to the code below:

Using guard-let:

guard let unwrappedResult = result as? [NSManagedObject] else {
        print("unwrap of result failed")
        return
 }
 for data in unwrappedResult {
     //perform your logic
 }

Using if-let:

if let unwrappedResult = result as? [NSManagedObject] {
   for data in unwrappedResult {
       //perform your logic
   }
}

edited Apr 25 '20 at 20:13

answered Apr 25 '20 at 19:59

Vikram Parimi

777
6
29

That code would not work either, since result would be optional. You should add `?? []` to the end. – Wyetro Apr 25 '20 at 20:01
@Wyetro Thanks for the highlight. I have updated my approach anyways :) – Vikram Parimi Apr 25 '20 at 20:13
Looks good! This would definitely be a way to solve the issue – Wyetro Apr 25 '20 at 20:14

Wyetro · Accepted Answer · 2020-04-25T20:24:03.870

1

You've misunderstood what the do-try-catch block does.

When you put the ? after try you are preventing the catch from getting hit. So if try fails, it is setting result to nil. Then you are force casting nil to [NSManagedObject].

You have two options:

Remove the ? after try
Like Vikram mentioned, don't force cast result, use as? [NSManagedObject]

1)

do {
    let result = try context.fetch(request)
    for data in result as! [NSManagedObject] {
        FacialViewControllerA = data.value(forKey: "titleA") as! String
    }
} catch {
    print("There was an error: \(error)")
}

2)

if let result = try? context.fetch(request) as? [NSManagedObject] {
    for data in result  {
        FacialViewControllerA = data.value(forKey: "titleA") as! String
    }
}

edited Apr 25 '20 at 20:24

answered Apr 25 '20 at 20:04

Wyetro

8,439
9
46
64

thank you for the answer, but when i remove (try) it gives me the error: "Errors thrown from here are not handled" – Myz Apr 25 '20 at 20:15
1

@MyzXI you have to add the `catch` part of the block. I've updated my answer with code examples – Wyetro Apr 25 '20 at 20:20
1

thank you, works like a charm :) – Myz Apr 25 '20 at 20:22
1

@MyzXI glad I was able to help! – Wyetro Apr 25 '20 at 20:23

I keep Getting The Error: Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

2 Answers2