"The Data Couldn't Be Read Because It Is Missing" Error When Decoding JSON in Swift

The data couldn’t be read because it is missing error when decoding JSON in Swift

I just solved a similar issue on my end but for the property list decoder.

The error in this case seems to mean that a key wasn't found and not the data as a whole.

Try making the variables in your struct optional and it should return a nil value where the problem lies.

JSON API Error- The data couldn’t be read because it is missing.- in iOS, swift

First of all the Codable models that you're using is missing the root level object of the JSON. So, you must use

struct Root: Codable {
    let items: [Items]
}

struct Items: Codable {
    let title:String?
    let snippet:String?
    let pagemap : PageMap?
}

struct PageMap: Codable {
    let cseImage: [Thumbnail]?
}

struct Thumbnail: Codable {
    let src: String?
}

Important:

1. No need for enum CodingKeys if the property names exactly match the JSON keys.
2. No need for init(from:) if you're not doing any specific parsing.
3. Don't use var when not required. Use let instead while declaring the properties.
4. If you're using convertFromSnakeCase while parsing, you must create the property names in camel-case (without underscore).

Next, your parsing code in URLSession must go like,

URLSession.shared.dataTask(with: url) { (data, response, error) in
    if let data = data {
        let decoder = JSONDecoder()
        decoder.keyDecodingStrategy = .convertFromSnakeCase
        let res = try decoder.decode(Root.self, from: data)
        //rest of the code...
    }
}

Problem while converting JSON to Swift The data couldn’t be read because it isn’t in the correct format.

First of all

never print(error.localizedDescription).

in a JSONDecoder catch block. You get a generic but quite meaningless error message.

Always print the entire error, DecodingErrors are very descriptive

print(error)

---

Your code contains three major errors, one of them (error #3) occurs multiple times

Error #1

typeMismatch(Swift.Dictionary<Swift.String, Any>, Swift.DecodingError.Context(codingPath: [], debugDescription: "Expected to decode Dictionary<String, Any> but found an array instead.", underlyingError: nil))

indicates that the root object is an array, the JSON starts clearly with [

Solution: Decode [CryptListStruct].self

---

Error #2

dataCorrupted(Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "volume_1mth_usd", intValue: nil)], debugDescription: "Parsed JSON number <3699822674922524.74> does not fit in Int.", underlyingError: nil))

indicates that the received value 3699822674922524.74 is actually a Double.

Solution: Declare

let volume1MthUsd: Double

---

Error #3

keyNotFound(CodingKeys(stringValue: "id_icon", intValue: nil), Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 4", intValue: 4)], debugDescription: "No value associated with key CodingKeys(stringValue: "id_icon", intValue: nil) ("id_icon").", underlyingError: nil))

indicates that the key id_icon is missing (at least) in the 5th item of the array.

Solution: Declare the type as optional

let idIcon : String?

The same error occurs for dataTradeStart, dataTradeEnd, dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd, dataStart, dataEnd

let dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd: String?
let dataTradeStart, dataTradeEnd : String?
let dataStart, dataEnd: String?

---

Side note:

You can delete the entire CodingKeys enum if you replace assetID with assetId and add the convertFromSnakeCase key decoding strategy

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let crpytList = try decoder.decode([CryptListStruct].self, from: data)

Swift - The data couldn’t be read because it isn’t in the correct format

Try this

let gitData = try decoder.decode(Root.self, from: data!)

Traverse through your data

for singleData in gitData.data where (singleData.name ?? "") == "Cafe" {
    print(singleData.image)
}

Swift The data couldn’t be read because it isn’t in the correct format

Your JSON format doesn't quite match what you're trying to decode. You need a wrapper for the latest_photos array at the root of your JSON object.

For example:

struct LatestPhotosWrapper: Codable {
    let latestPhotos: [LatestPhoto]
    
    enum CodingKeys: String, CodingKey {
        case latestPhotos = "latest_photos"
    }
}

let apod = try JSONDecoder().decode(LatestPhotosWrapper.self, from: data)

(Rather than providing a CodingKey, you can also look into the built-in systems for converting from snake case: https://developer.apple.com/documentation/foundation/jsondecoder/keydecodingstrategy/convertfromsnakecase)

Also, you may want to print the error and not just the error.localizedDescription -- you can get a better picture of what's going on. For example, with your original code, you get:

Expected to decode Array but found a dictionary instead.

Finally, you might check out app.quicktype.io -- you can paste in your JSON and get correct Swift structs pre-built for you.

The data couldn’t be read because it is missing. GET Request

You have to add this in your DriverProfileStruct struct. Because in codable you have to decode key using CodingKey if is different from your variable name

enum CodingKeys: String, CodingKey {
        case autoType = "auto_type"
}

---

Related Topics