Why do I get ‘Cannot get keyed decoding container -- found null value instead.’ error when I use JSONDecoder

Question

(unknown context at $10741e078).CodingKeys>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Cannot get keyed decoding container -- found null value instead.", underlyingError: nil)

my model is ,

struct Details : Decodable {

    var userInfo : RequestUserInfo
    var commercialInfo : String?

}

struct RequestUserInfo : Decodable {

    var UserName : String?
    var Email : String?
    var UserIdentity : String?
    var UserMobile : String?
    var ThirdName : String?
    var LastName : String?
    var IdIssueDate : String?
    var IdSourceCity : String?


}

(unknown context at $10741e078).CodingKeys>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Cannot get keyed decoding container -- found null value instead.", underlyingError: nil)

add the code and api.. – Shivam Parmar Dec 24 '19 at 11:47 — Shivam Parmar, Dec 24 '19 at 11:47
please post json and models – Shehata Gamal Dec 24 '19 at 11:47 — Shehata Gamal, Dec 24 '19 at 11:47
I have posted the json and the models – Faheem Rahman Dec 24 '19 at 12:05 — Faheem Rahman, Dec 24 '19 at 12:05
For future, include the error in your question’s title. – mfaani Dec 24 '19 at 15:52 — mfaani, Dec 24 '19 at 15:52

PGDev · Accepted Answer · 2019-12-24T12:50:29.570

6

You need to mark the types as Optional (?) wherever you're expecting null in the JSON.

But, the issue with the above parsing is different from the one you described in the question.

typeMismatch(Swift.String, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "newRequest", intValue: nil), CodingKeys(stringValue: "parcels", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "UsingPurposeId", intValue: nil)], debugDescription: "Expected to decode String but found a number instead.", underlyingError: nil))

This can be resolved like so,

The type of UsingPurposeId in BuildingRequestParcelDetails must be Int? instead of String?

Parse the data in following way,

do {
    let response = try JSONDecoder().decode(BuildingRequestDetails.self, from: data)
    print(response)
} catch {
    print(error)
}

edited Dec 24 '19 at 12:50

answered Dec 24 '19 at 12:45

PGDev

23,751
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I am parsing this way only . Please check my question. I am still getting error . – Faheem Rahman Dec 24 '19 at 12:49
1

Are you sure you're getting the same JSON. Because with this json and changing to Int?, it is working perfectly at my end. – PGDev Dec 24 '19 at 12:51
1

I've checked with your JSON and @PGDev answer - everything works correctly – Vadim Nikolaev Dec 24 '19 at 12:51
yes i am getting this JSON . I have copied and pasted it here – Faheem Rahman Dec 24 '19 at 12:54
i used Int? itself – Faheem Rahman Dec 24 '19 at 12:55

score 0 · Answer 2 · answered Dec 24 '19 at 12:10

0

you can use this ModelAPI - https://app.quicktype.io?share=NYC0PgFnypeo5cLho3sH and call it with code self.requestDetail = try JSONDecoder().decode(ModelAPI.self, from: json). I've checked and it works. Also, I've fixed your JSON (error with two lines)

answered Dec 24 '19 at 12:10

Vadim Nikolaev

2,132
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The error description pretty much says it all: "Cannot get keyed decoding container — found null value instead". Now I check your model, also, as I wrote - "Invalid JSON variable". Give a few minutes - check it. – Vadim Nikolaev Dec 24 '19 at 12:20
I have fixed the issue in JSON . – Faheem Rahman Dec 24 '19 at 12:31
why should i change that? – Faheem Rahman Dec 24 '19 at 12:43
`struct BuildingRequestParcelDetails : Decodable` has property `var UsingPurposeId : String?`. You should replace it with `var UsingPurposeID : String?`. When I changed - everything worked correctly. And @PGDev is right - you can just change the type to `Int?` and then everything will work too – Vadim Nikolaev Dec 24 '19 at 12:45

score 0 · Answer 3 · answered Dec 24 '19 at 15:25

In your case this may happens if Details.userInfo == nil

set

var userInfo : RequestUserInfo?

And your error will disappear. But in fact your error hides in wrong data. Try before decoding add string:

print(String(data:  data, encoding: .ascii))

and check carefully is anything is ok. For example, you may get "user_info" instead key "userInfo"

score 0 · Answer 4 · answered Jul 04 '22 at 15:30

If you are JSON decoding to a Codable object mapped to Core Data then you can use a do try method. For example with an object which may have a set of names.

    do {
        names = NSSet(array: try 
        container.decode([Name].self, forKey: .names))
    } catch {
        print("no names found")
    }

If no names are within the JSON then no names found will be printed and the JSON decoder won't return an error

Why do I get ‘Cannot get keyed decoding container -- found null value instead.’ error when I use JSONDecoder

4 Answers4