Swift: unexpectedly found nil while unwrapping an Optional value

Question

var session = NSUserDefaults.standardUserDefaults().stringForKey("session")!
println(session)

I am getting crash with following error:

fatal error: unexpectedly found nil while unwrapping an Optional value

There are 430 search results for `[swift] "unexpectedly found nil while unwrapping an Optional value"` and 6 results for `[swift] NSUserDefaults "unexpectedly found nil while unwrapping an Optional value"` – Are you sure that none of them solves your problem? — Martin R, May 28 '15 at 08:00
@MartinR Yeah I saw few search results and everyone has posted entire source code. Being a fresher its impossible to go through hundreds of line of code to figure out my issue. — Riya Khanna, May 28 '15 at 08:18
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) — Cristik, Mar 19 '18 at 06:01

Tariq · Accepted Answer · 2015-05-30T07:30:45.550

9

You're getting crash due to the forced unwrapping operator ! which is attempting to force unwrap a value from a nil optional.

The forced unwrapping operator should be used only when an optional is known to contain a non-nil value.

You can use optional binding:

if let session = NSUserDefaults.standardUserDefaults().stringForKey("session") {
    printString(session)
}

edited May 30 '15 at 07:30

answered May 28 '15 at 07:51

Tariq

5

Downvoters, care to comment. Whats wrong with the solution? Being a 6 years of active member on stackoverflow I know its so easy to click downvote button, but don't ever to do that without proper comments. – Tariq May 30 '15 at 07:29
For your comment and answer you get one UPvote - I agree, people are here to learn, and noobs (like myself) get put off when people downvote. We just need a little guidance is all.. – JamesG Feb 29 '16 at 10:25

Leo Dabus · Answer 2 · 2016-12-19T17:16:40.300

8

you should use the nil coalescing operator "??"

let session = NSUserDefaults.standardUserDefaults().stringForKey("session") ?? ""

Xcode 8.2 • Swift 3.0.2

let session = UserDefaults.standard.string(forKey: "session") ?? ""

edited Dec 19 '16 at 17:16

answered May 28 '15 at 07:50

Leo Dabus

score 1 · Answer 3 · answered May 28 '15 at 07:49

You need to remove the ! at the end or you need to check before you unwrap if like this:

If there is a value at that location put in the session constant and execute the block of the if, if not skip the if block

if let session = NSUserDefaults.standardUserDefaults().stringForKey("session") {
    println(session)
}

You should take a look over the Swift documentation regarding Optional type here

3 Answers3