Error when parsing JSON in Swift 3

Question

I am working on an iOS app in Swift 3, and I make a call to a server and get json back and serialize it.

When I try to parse it I get this error:

"Could not cast value of type '__NSArrayI' (0x1a779acc8) to 'NSDictionary' (0x1a779b128). 2017-03-16 09:53:00.710776 AutoBuddy[3164:706970] Could not cast value of type '__NSArrayI' (0x1a779acc8) to 'NSDictionary' (0x1a779b128)."

I have seen a couple other versions of this question, but I am still confused. From what I can tell, the JSON comes back as a dictionary with key value pairs [String:Any].

I tried explicitly casting the result of the call "as? Dictionary< String, Any > but that failed. It doesn't make sense to me, because I appear to be getting a dictionary, but it doesn't behave as one. Currently the program is crashing on the first line of my parseJSON function. I have a feeling that the problem is either how I am getting the json back, or how I serialize it, because I have used a similar parsing method before and it always worked. Or if it is a parsing problem, could someone explain to me the proper way to parse this out? I will post the code and an example of the JSON that it serializes.

JSON:

["id": 745, "year": 1995, "styles": <__NSArrayI 0x170e68f00>(
{
    id = 7654;
    name = "2dr Coupe";
    submodel =     {
        body = Coupe;
        modelName = "Mustang Coupe";
        niceName = coupe;
    };
    trim = Base;
},
{
    id = 7653;
    name = "2dr Convertible";
    submodel =     {
        body = Convertible;
        modelName = "Mustang Convertible";
        niceName = convertible;
    };
    trim = Base;
},
{
    id = 7648;
    name = "GT 2dr Coupe";
    submodel =     {
        body = Coupe;
        modelName = "Mustang Coupe";
        niceName = coupe;
    };
    trim = GT;
},
{
    id = 7647;
    name = "GT 2dr Convertible";
    submodel =     {
         body = Convertible;
         modelName = "Mustang Convertible";
         niceName = convertible;
    };
    trim = GT;
},
{
    id = 7650;
    name = "GTS 2dr Coupe";
    submodel =     {
        body = Coupe;
        modelName = "Mustang Coupe";
        niceName = coupe;
    };
    trim = GTS;
}
)
]

Swift Code:

func getJSONData(path: String)
{
let config = URLSessionConfiguration.default 
    let session = URLSession(configuration: config) 
    let url = URL(string: path + "API key")!

    let task = session.dataTask(with: url, completionHandler:
        {
            (data, response, error) in
            if error != nil
            {
                print(error!.localizedDescription)
            }
            else
            {
                do {
                    if let resultJSON = try JSONSerialization.jsonObject(with: data!) as? [String: Any]
                    {
                        print(resultJSON)
                        self.parseJSON(json: resultJSON)
                    }
                }
                catch
                {
                    print("\(error)")
                }
            }
    })
    task.resume()
}
func parseJSON(json: [String: Any])
{
    let styles = json["styles"] as! [String:Any] // Crashes Here
    print(styles)
    let names = styles["name"] as! String
    print(names)
}

Answer 1

Please read the JSON carefully, it's very easy:

• [] represents an array, in Swift [[String:Any]] or sometimes [Any]
• {} represents a dictionary, in Swift [String:Any].

The value for styles is clearly an array (even indicated in clear text: "styles": <__NSArrayI 0x170e68f00>)

let styles = json["styles"] as! [[String:Any]]

and you need a repeat loop to get the names

for style in styles {
   let name = style["name"] as! String
   print(name)
}

or you can use flatMap

let names = styles.flatMap { $0["name"] as? String }
print(names)

PS: The root object of the JSON seems also to be an array, if so you need to cast

if let resultJSON = try JSONSerialization.jsonObject(with: data!) as? [[String: Any]]

And then you have to change also

func parseJSON(json: [[String: Any]]) {
   let styles = json[0]["styles"] as! [[String:Any]]

---

To avoid square-bracket-confusion I recommend to use a type alias:

typealias JSONDictionary = [String:Any]

Then a dictionary is JSONDictionary, an array of dictionaries is [JSONDictionary], easy to distinguish.

Answer 2

struct Course: Decodable {
    let id: Int?
    let name: String?
    let link: String?
    let imageUrl: String?

}


func Callservice()
{
    var arrayData:[Course] = []
    let jsonUrlString = "someUrl"
    guard let url = URL(string: jsonUrlString) else { return }

    URLSession.shared.dataTask(with: url) { (data, response, err) in
        guard let data = data else { return }
        do {

            let courses = try JSONDecoder().decode([Course].self, from: data)
            self.arrayData = courses

            print(courses)


        } catch let jsonErr {
            print("Error serializing json:", jsonErr)
        }



        }.resume()
}

Answer 3

I eventually solved the issue, just in case anyone is using this as a reference.

func getJSONData(path: String)
{
    let config = URLSessionConfiguration.default // Session Configuration
    let session = URLSession(configuration: config) // Load configuration into Session
    let url = URL(string: path + API_Key)!

    let task = session.dataTask(with: url, completionHandler:
        {
            (data, response, error) in
            if error != nil
            {
                print(error!.localizedDescription)
            }
            else
            {
                do {
                    let resultJSON = try JSONSerialization.jsonObject(with: data!) as! [String: Any]
                    let styles = resultJSON["styles"] as! NSArray
                    for i in 0..<styles.count
                    {
                        let name = styles[i] as! Dictionary<String, Any>
                        self.trims.append(name["name"] as! String)
                    }
                    DispatchQueue.main.async() {
                        self.tableView.reloadData()
                        self.tableView.isHidden = false
                        return
                    }
                }
                catch
                {
                    print("Error: \(error)")
                }
            }
    })
    task.resume()
}