JSON Parsing in Swift 3

Question

Has anyone been able to find a way to parse through JSON files in Swift 3? I have been able to get the data to return but I am unsuccessful when it comes to breaking the data down into specific fields. I would post sample code but I've gone through so many different methods unsuccessfully and haven't saved any. The basic format I want to parse through is something like this. Thanks in advance.

{
  "Language": {

    "Field":[
          {
          "Number":"976",
          "Name":"Test"
          },
          {
          "Number":"977",
          "Name":"Test"
          }
       ]
   }
}

Answer 1

Have you tried JSONSerialization.jsonObject(with:options:)?

var jsonString = "{" +     "\"Language\": {" +     "\"Field\":[" +     "{" +     "\"Number\":\"976\"," +     "\"Name\":\"Test\"" +     "}," +     "{" +     "\"Number\":\"977\"," +     "\"Name\":\"Test\"" +     "}" +     "]" +     "}" +     "}"  var data = jsonString.data(using: .utf8)!  let json = try? JSONSerialization.jsonObject(with: data) 

---

Swift sometimes produces some very odd syntax.

if let number = json?["Language"]??["Field"]??[0]?["Number"] as? String {     print(number) } 

Everything in the JSON object hierarchy ends up getting wrapped as an optional (ie. AnyObject?). Array<T> subscript returns a non-optional T. For this JSON, which is wrapped in an optional, array subscript returns Optional<AnyObject>. However, Dictionary<K, V> subscript returns an Optional<V>. For this JSON, subscript returns the very odd looking Optional<Optional<AnyObject>> (ie. AnyObject??).

• json is an Optional<AnyObject>.
• json?["Language"] returns an Optional<Optional<AnyObject>>.
• json?["Language"]??["Field"] returns an Optional<Optional<AnyObject>>.
• json?["Language"]??["Field"]??[0] returns an Optional<AnyObject>.
• json?["Language"]??["Field"]??[0]?["Number"] returns an Optional<Optional<AnyObject>>.
• json?["Language"]??["Field"]??[0]?["Number"] as? String returns an Optional<String>.

The Optional<String> is then used by the if let syntax to product a String.

---

Final note: iterating the field array looks like this.

for field in json?["Language"]??["Field"] as? [AnyObject] ?? [] {     if let number = field["Number"] as? String {         print(number)     } } 

---

Swift 4 Update

Swift 4 makes this all much easier to deal with. Again we will start with your test data (""" makes this so much nicer).

let data = """ {   "Language": {      "Field":[           {           "Number":"976",           "Name":"Test"           },           {           "Number":"977",           "Name":"Test"           }        ]    } } """.data(using: .utf8)! 

---

Next we can define classes around the objects used in your JSON.

struct Object: Decodable {     let language: Language     enum CodingKeys: String, CodingKey { case language="Language" } }  struct Language: Decodable {     let fields: [Field]     enum CodingKeys: String, CodingKey { case fields="Field" } }  struct Field: Decodable {     let number: String     let name: String     enum CodingKeys: String, CodingKey { case number="Number"; case name="Name" } } 

The CodingKeys enum is how struct properties are mapped to JSON object member strings. This mapping is done automagically by Decodable.

---

Parsing the JSON now is simple.

let object = try! JSONDecoder().decode(Object.self, from: data)  print(object.language.fields[0].name)  for field in object.language.fields {     print(field.number) } 

Answer 2

In Xcode 8 and Swift 3 id now imports as Any rather than AnyObject

This means that JSONSerialization.jsonObject(with: data) returns Any. So you have to cast the json data to a specific type like [String:Any]. Same applies to the next fields down the json.

var jsonString = "{" +     "\"Language\": {" +     "\"Field\":[" +     "{" +     "\"Number\":\"976\"," +     "\"Name\":\"Test1\"" +     "}," +     "{" +     "\"Number\":\"977\"," +     "\"Name\":\"Test2\"" +     "}" +     "]" +     "}" + "}"  var data = jsonString.data(using: .utf8)! if let parsedData = try? JSONSerialization.jsonObject(with: data) as! [String:Any] {     let language = parsedData["Language"] as! [String:Any]     print(language)     let field = language["Field"] as! [[String:Any]]     let name = field[0]["Name"]!     print(name) // ==> Test1 } 

In practice you would probably want some specific field buried in the json. Lets assume it's the Name field of the first element of Field array. You can use a chain of unwraps like this to safely access the field:

var data = jsonString.data(using: .utf8)! if let json = try? JSONSerialization.jsonObject(with: data) as? [String:Any],     let language = json?["Language"] as? [String:Any],     let field = language["Field"] as? [[String:Any]],     let name = field[0]["Name"] as? String, field.count > 0 {     print(name) // ==> Test1 } else {     print("bad json - do some recovery") } 

Also you may want to check Apple's Swift Blog Working with JSON in Swift

Answer 3

Shoving JSON into a string manually is a pita. Why don't you just put the JSON into a file and read that in?

Swift 3:

let bundle = Bundle(for: type(of: self))
    if let theURL = bundle.url(forResource: "response", withExtension: "json") {
        do {
            let data = try Data(contentsOf: theURL)
            if let parsedData = try? JSONSerialization.jsonObject(with: data) as! [String:Any] {
                grok(parsedData)
            }
        } catch {
            print(error)
        }
    }