please give me some solution to this error Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

Question

func doGetLocalDataUser() -> logInResponse {
     var localData : logInResponse? = nil
     if let userData = UserDefaults.standard
                                    .data(forKey: ConstantStrings.KEY_USER_LOGIN_DATA),let user = try? JSONDecoder()
                                    .decode(logInResponse.self ,from: userData){
                                            localData = user
                                    }
        return localData!
    }

if logInResponse != nil then if UserDefaults.standard.data(forKey: ConstantStrings.KEY_USER_LOGIN_DATA) != nil maybe...anyway, start learning to think before code. No rude, just a clear advice. Play with guard for safe. You tell in code localData is optional, then you return as ! — ares777, Apr 25 '19 at 08:56
You didn't even bother to paste the error in Google, because there's like 10 different links to SO with answers to that question — mag_zbc, Apr 25 '19 at 09:00

10623169 · Answer 1 · 2019-04-25T09:07:11.600

localData is nil, so you are force unwrapping localData (as a logInResponse) illegally.

If your optional chaining finds nil at any point (for example your userData doesn't exist in UserDefaults / has the wrong type) then it won't execute.

You are declaring this doGetLocalDataUser() function to return a non optional logInResponse type and force unwrapping a nil value to try and retrieve one. Best practice is to avoid the force unwrap "bang" operator "!" because it can lead to fatal errors like this.

Simple solution is to change your method to return an optional logInResponse? type, and eliminate the bang operator:

func doGetLocalDataUser() -> logInResponse? {
    if let userData = UserDefaults.standard.data(forKey: ConstantStrings.KEY_USER_LOGIN_DATA), let user = try? JSONDecoder().decode(logInResponse.self ,from: userData){
        return user
    } else {
        return nil
    }
}

score 0 · Answer 2 · answered Apr 25 '19 at 09:03

I would change the method to this:

func doGetLocalDataUser() -> logInResponse? {
    guard let userData = UserDefaults.standard.data(forKey: ConstantStrings.KEY_USER_LOGIN_DATA), let user = try? JSONDecoder().decode(logInResponse.self ,from: userData) else {
        return nil
    }

    return user
}

Keep in mind JSON decoding can fail (maybe has wrong format), therefore user will be nil, and this method can return nil

please give me some solution to this error Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

2 Answers2