Creating a certain JSON data structure in Swift - json

Question

For backend communication, my app requires a method to create a certainly structured JSON, and thats where i struggle.
The created JSON is supposed to look like this:
{
"data": {
"color":"yellow",
"size":"big"
}
}
Serializing a Dictionary with the required Data does not really seem to have the option to format the content properly, my best results look like this:
Optional({
Kategorie = Strassenschaeden;
PLZ = 46282;
Strasse = Erftweg;
Unterkategorie = Schlagloch;
})
I didnt find any helpful weblinks for my problem, and since im new to Swift and its documentation Im kinda stuck at the moment.
So my questions are:
Whats the preferred data structure for my JSON data (Dictionary/Array) and how do I create a JSON that is well-formated?
Thanks in advance :)
Edit: This is the interesting part of what i have used to achieve my "best result":
var data: [String: String] = ["Kategorie": "\(Kategorie)", "Unterkategorie": "\(Unterkategorie)", "Strasse": "\(Strasse)","PLZ": "\(PLZ)"]
self.post(data, url: "http://*************") { (succeeded: Bool, msg: String) -> () in
var alert = UIAlertView(title: "Success!", message: msg, delegate: nil, cancelButtonTitle: "Okay.")
func post(params : Dictionary<String, String>, url : String, postCompleted : (succeeded: Bool, msg: String) -> ()) {
var request = NSMutableURLRequest(URL: NSURL(string: url)!)
let JSONData:NSData = NSJSONSerialization.dataWithJSONObject(params, options: NSJSONWritingOptions.PrettyPrinted, error: &err)!
var json = NSJSONSerialization.JSONObjectWithData(JSONData, options: nil, error: &err) as? NSDictionary
println(json)

Answer 1

Here
let JSONData:NSData = NSJSONSerialization.dataWithJSONObject(params, options: NSJSONWritingOptions.PrettyPrinted, error: &err)!
var json = NSJSONSerialization.JSONObjectWithData(JSONData, options: nil, error: &err) as? NSDictionary
you are converting the params dictionary to JSON data – and then you convert the
JSON data back do a dictionary! What you probably want is to create a string
from the JSON data:
let jsonData = NSJSONSerialization.dataWithJSONObject(params, options: .PrettyPrinted, error: &err)!
let json = NSString(data: jsonData, encoding: NSUTF8StringEncoding)!
println(json)
Remarks:
Properties and variables should have names starting with lower case letters, e.g.
jsonData.
The explicit type annotation :NSData is not needed here, the Swift compiler can
infer the type automatically.
The option can be given as .PrettyPrinted instead of NSJSONWritingOptions.PrettyPrinted, the compiler infers the enumeration type
automatically.
Instead of forced unwrapping with ! you should use optional binding to check
for success.

Answer 2

Just an itch, that no one here recommend swiftyJSON for working with JSON in Swift.
Try it, you will lose your pain of dealing with JSON.
https://github.com/SwiftyJSON/SwiftyJSON
To Read JSON
let jsonData = jsonString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
let jsonObject = JSON(data: jsonData!)
To Write JSON
let jsonString = jsonObject.rawString()