ios - Swift 4 The data couldn’t be read because it isn’t in the correct format

Question

I am developing a project to learn how to parse JSON. I am trying to parse JSON to a struct. I am trying to do it using the code that comes next but I am getting the following error:

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

What am I doing wrong? Also I tried to use Alamofire but I didn't find way to parse it to struct.

func getData(){
    let gitUrl = URL(string: "http://95.46.99.250:9095/api/v1/institution-categories")
    URLSession.shared.dataTask(with: gitUrl!) { (data, response
        , error) in
        let data = data
        print(data)
        do {
            let decoder = JSONDecoder()
            let gitData = try decoder.decode([Root].self, from: data!)

        } catch let err {
            print("
Err", err.localizedDescription)
        }
        }.resume()
}

Struct

struct Root: Codable {
    let  data: [InnerItem]
}
struct InnerItem:Codable {
    let  id: Int?
    let  image: String?
    let  name: String?

    private enum CodingKeys : String, CodingKey {
        case id = "id", image = "image", name = "name"
    }
}

JSON

{
"data": [
    {
        "id": 1,
        "name": "Пабы и бары",
        "image": "http://95.46.99.250:9095/storage/photos/beer@2x.png"
    },
    {
        "id": 2,
        "name": "Кафе",
        "image": "http://95.46.99.250:9095/storage/photos/coffee@3x.png"
    },
    {
        "id": 3,
        "name": "Ночной клуб",
        "image": "http://95.46.99.250:9095/storage/photos/0201f7523bc2028f174710b51379e432.png"
    },
    {
        "id": 4,
        "name": "Ресторан",
        "image": "http://95.46.99.250:9095/storage/photos/restaurants@3x.png"
    },
    {
        "id": 5,
        "name": "Караоке-клуб",
        "image": "http://95.46.99.250:9095/storage/photos/microphone.png"
    },
    {
        "id": 6,
        "name": "Суши-бар",
        "image": "http://95.46.99.250:9095/storage/photos/sushi.png"
    },
    {
        "id": 7,
        "name": "Пиццерии",
        "image": "http://95.46.99.250:9095/storage/photos/pizza.png"
    },
    {
        "id": 8,
        "name": "Кальянная",
        "image": "http://95.46.99.250:9095/storage/photos/c111d1e5ad6b90b61ac36836d220ebba.png"
    },
    {
        "id": 9,
        "name": "Общая",
        "image": "http://95.46.99.250:9095/storage/photos/Group 315@3x.png"
    }
]
}

Answer 1

?? Troubleshoot coding/decoding errors

When working with codables, instead of printing .localizedDescription, try to print out the error itself! so the compiler describes where the issue exactly is!

do {
    let decoder = JSONDecoder()
    let decoded = try decoder.decode([Root].self, from: data!)
} catch {
    // print(localizedDescription) // <- ?? Don't use this!

    print(String(describing: error)) // <- ? Use this for debuging!
}

---

In your case

it will point out that:

• Decoder tried to decode the root object to an Array but found a Dictionary instead.

So you follow the issue and see that you should replace:

decoder.decode([Root].self, from: data!)

with:

decoder.decode(Root.self, from: data!)