Convert array to JSON string in swift

How do you convert an array to a JSON string in swift? Basically I have a textfield with a button embedded in it. When button is pressed, the textfield text is added unto the testArray. Furthermore, I want to convert this array to a JSON string.

This is what I have tried:

func addButtonPressed() {
    if goalsTextField.text == "" {
        // Do nothing
    } else {
        testArray.append(goalsTextField.text)
        goalsTableView.reloadData()
        saveDatatoDictionary()
    }
}

func saveDatatoDictionary() {
    data = NSKeyedArchiver.archivedDataWithRootObject(testArray)
    newData = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions(), error: nil) as? NSData
    string = NSString(data: newData!, encoding: NSUTF8StringEncoding) 
    println(string)
}

I would also like to return the JSON string using my savetoDictionart() method.

As it stands you're converting it to data, then attempting to convert the data to to an object as JSON (which fails, it's not JSON) and converting that to a string, basically you have a bunch of meaningless transformations.

As long as the array contains only JSON encodable values (string, number, dictionary, array, nil) you can just use NSJSONSerialization to do it.

Instead just do the array->data->string parts:

Swift 3/4

let array = [ "one", "two" ]

func json(from object:Any) -> String? {
    guard let data = try? JSONSerialization.data(withJSONObject: object, options: []) else {
        return nil
    }
    return String(data: data, encoding: String.Encoding.utf8)
}

print("\(json(from:array as Any))")

Original Answer

let array = [ "one", "two" ]
let data = NSJSONSerialization.dataWithJSONObject(array, options: nil, error: nil)
let string = NSString(data: data!, encoding: NSUTF8StringEncoding)

although you should probably not use forced unwrapping, it gives you the right starting point.

Swift 3.0 - 4.0 version

do {

    //Convert to Data
    let jsonData = try JSONSerialization.data(withJSONObject: dictionaryOrArray, options: JSONSerialization.WritingOptions.prettyPrinted)

    //Convert back to string. Usually only do this for debugging
    if let JSONString = String(data: jsonData, encoding: String.Encoding.utf8) {
       print(JSONString)
    }

    //In production, you usually want to try and cast as the root data structure. Here we are casting as a dictionary. If the root object is an array cast as [Any].
    var json = try JSONSerialization.jsonObject(with: jsonData, options: JSONSerialization.ReadingOptions.mutableContainers) as? [String: Any]
    

} catch {
    print(error.description)
}

The JSONSerialization.WritingOptions.prettyPrinted option gives it to the eventual consumer in an easier to read format if they were to print it out in the debugger.

Reference: Apple Documentation

The JSONSerialization.ReadingOptions.mutableContainers option lets you mutate the returned array's and/or dictionaries.

Reference for all ReadingOptions: [Apple Documentation] 2

NOTE: Swift 4 has the ability to encode and decode your objects using a new protocol. Here is Apples Documentation, and a quick tutorial for a starting example.

If you're already using SwiftyJSON:

https://github.com/SwiftyJSON/SwiftyJSON

You can do this:

// this works with dictionaries too
let paramsDictionary = [
    "title": "foo",
    "description": "bar"
]
let paramsArray = [ "one", "two" ]
let paramsJSON = JSON(paramsArray)
let paramsString = paramsJSON.rawString(encoding: NSUTF8StringEncoding, options: nil)

SWIFT 3 UPDATE

 let paramsJSON = JSON(paramsArray)
 let paramsString = paramsJSON.rawString(String.Encoding.utf8, options: JSONSerialization.WritingOptions.prettyPrinted)!

JSON strings, which are good for transport, don't come up often because you can JSON encode an HTTP body. But one potential use-case for JSON stringify is Multipart Post, which AlamoFire nows supports.

How to convert array to json String in swift 2.3

var yourString : String = ""
do
{
    if let postData : NSData = try NSJSONSerialization.dataWithJSONObject(yourArray, options: NSJSONWritingOptions.PrettyPrinted)
    {
        yourString = NSString(data: postData, encoding: NSUTF8StringEncoding)! as String
    }
}
catch
{
    print(error)
}

And now you can use yourSting as JSON string..

Swift 5

This generic extension will convert an array of objects to a JSON string from which it can either be:

• saved to the App's Documents Directory (iOS/MacOS)
• output directly to a file on the Desktop (MacOS)

.

extension JSONEncoder {
    static func encode<T: Encodable>(from data: T) {
        do {
            let jsonEncoder = JSONEncoder()
            jsonEncoder.outputFormatting = .prettyPrinted
            let json = try jsonEncoder.encode(data)
            let jsonString = String(data: json, encoding: .utf8)
            
            // iOS/Mac: Save to the App's documents directory
            saveToDocumentDirectory(jsonString)
            
            // Mac: Output to file on the user's Desktop
            saveToDesktop(jsonString)
            
        } catch {
            print(error.localizedDescription)
        }
    }
    
    static private func saveToDocumentDirectory(_ jsonString: String?) {
        guard let path = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
        let fileURL = path.appendingPathComponent("Output.json")
        
        do {
            try jsonString?.write(to: fileURL, atomically: true, encoding: .utf8)
        } catch {
            print(error.localizedDescription)
        }
        
    }
    
    static private func saveToDesktop(_ jsonString: String?) {
        let homeURL = FileManager.default.homeDirectoryForCurrentUser
        let desktopURL = homeURL.appendingPathComponent("Desktop")
        let fileURL = desktopURL.appendingPathComponent("Output.json")
        
        do {
            try jsonString?.write(to: fileURL, atomically: true, encoding: .utf8)
        } catch {
            print(error.localizedDescription)
        }
    }
}

Example:

struct Person: Codable {
    var name: String
    var pets: [Pet]
}

struct Pet: Codable {
    var type: String
}

extension Person {
    static func sampleData() -> [Person] {
        [            Person(name: "Adam", pets: []),
            Person(name: "Jane", pets: [
                    Pet(type: "Cat")
            ]),
            Person(name: "Robert", pets: [
                    Pet(type: "Cat"),
                    Pet(type: "Rabbit")
            ])
        ]
    }
}

Usage:

JSONEncoder.encode(from: Person.sampleData())

Output:

This will create the following correctly formatted Output.json file:

[  {    "name" : "Adam",    "pets" : [    ]
  },
  {
    "name" : "Jane",
    "pets" : [
      {
        "type" : "Cat"
      }
    ]
  },
  {
    "name" : "Robert",
    "pets" : [
      {
        "type" : "Cat"
      },
      {
        "type" : "Rabbit"
      }
    ]
  }
]

SWIFT 2.0

var tempJson : NSString = ""
do {
    let arrJson = try NSJSONSerialization.dataWithJSONObject(arrInvitationList, options: NSJSONWritingOptions.PrettyPrinted)
    let string = NSString(data: arrJson, encoding: NSUTF8StringEncoding)
    tempJson = string! as NSString
}catch let error as NSError{
    print(error.description)
}

NOTE:- use tempJson variable when you want to use.

extension Array where Element: Encodable {
    func asArrayDictionary() throws -> [[String: Any]] {
        var data: [[String: Any]] = []
    
        for element in self {
            data.append(try element.asDictionary())
        }
        return data
    }
}

extension Encodable {
        func asDictionary() throws -> [String: Any] {
            let data = try JSONEncoder().encode(self)
            guard let dictionary = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as? [String: Any] else {
                throw NSError()
            }
            return dictionary
        }
}

If you're using Codable protocols in your models these extensions might be helpful for getting dictionary representation (Swift 4)

Hint: To convert an NSArray containing JSON compatible objects to an NSData object containing a JSON document, use the appropriate method of NSJSONSerialization. JSONObjectWithData is not it.

Hint 2: You rarely want that data as a string; only for debugging purposes.

For Swift 4.2, that code still works fine

 var mnemonic: [String] =  ["abandon",   "amount",   "liar", "buyer"]
    var myJsonString = ""
    do {
        let data =  try JSONSerialization.data(withJSONObject:mnemonic, options: .prettyPrinted)
       myJsonString = NSString(data: data, encoding: String.Encoding.utf8.rawValue) as! String
    } catch {
        print(error.localizedDescription)
    }
    return myJsonString

For Swift 3.0 you have to use this:

var postString = ""
    do {
        let data =  try JSONSerialization.data(withJSONObject: self.arrayNParcel, options: .prettyPrinted)
        let string1:String = NSString(data: data, encoding: String.Encoding.utf8.rawValue) as! String
        
        postString = "arrayData=\(string1)&user_id=\(userId)&markupSrcReport=\(markup)"
    } catch {
        print(error.localizedDescription)
    }
    request.httpBody = postString.data(using: .utf8)

100% working TESTED

Swift 5

Make sure your object confirm Codable.

Swift's default variable types like Int, String, Double and ..., all are Codable that means we can convert theme to Data and vice versa.

For example, let's convert array of Int to String Base64

let array = [1, 2, 3]
let data = try? JSONEncoder().encode(array)
nsManagedObject.array = data?.base64EncodedString()

Make sure your NSManaged variable type is String in core data schema editor and custom class if your using custom class for core data objects.

let's convert back base64 string to array:

var getArray: [Int] {
    guard let array = array else { return [] }
    guard let data = Data(base64Encoded: array) else { return [] }
    guard let val = try? JSONDecoder().decode([Int].self, from: data) else { return [] }
    return val
}

Do not convert your own object to Base64 and store as String in CoreData and vice versa because we have something that named Relation in CoreData (databases).

You can try this.

func convertToJSONString(value: AnyObject) -> String? {
        if JSONSerialization.isValidJSONObject(value) {
            do{
                let data = try JSONSerialization.data(withJSONObject: value, options: [])
                if let string = NSString(data: data, encoding: String.Encoding.utf8.rawValue) {
                    return string as String
                }
            }catch{
            }
        }
        return nil
    }