Swift creating JSON data from AnyObject - json

Question

Unfortunately I didn't find anything useful for writing JSON data on the internet. I wanted to ask what I have to do to let a class become a 'valid JSON object' that can be converted to JSON using NSJSONSerialization.dataWithJSONObject(<AnyObject>, options: .allZeros, error: nil). Does data have to be either a value like String or NSNumber or an object such as Array<AnyObject> or Dictionary<String, AnyObject>, which are objects that can easily be represented in JSON or are there any other possibilities to convert a JSON object? Thanks for your answers

Answer 1

NSJSONSerialization Class Reference:
An object that may be converted to JSON must have the following
properties:
The top level object is an NSArray or NSDictionary.
All objects are instances of NSString, NSNumber, NSArray,
NSDictionary, or NSNull.
All dictionary keys are instances of NSString.
Numbers are not NaN or infinity.
If you have other objects you have to manually convert them to one of these basic objects. So basically String and NSNumber. As far as I know there is no protocol that you can implement to turn your class into a JSONSerializable object.
In my opinion the best way to get your own objects into JSON is to create a method that returns a dictionary that only contains the allowed types. For the opposite way you can create a init that takes a dictionary.
Such an implementation would look like this:
class FancyObject {
let color: UIColor
let creationDate: NSDate
let title: String
init(title: String, color: UIColor) {
self.color = color
self.title = title
self.creationDate = NSDate()
}
init(dictionary: [String : AnyObject]) {
let colorString = dictionary["color"] as String
self.color = UIColor(rgbaString: colorString)!
self.title = dictionary["title"] as String
let dateString = dictionary["creationDate"] as String
self.creationDate = posixDateFormatter().dateFromString(dateString)!
}
func jsonRepresentation() -> [String : AnyObject] {
var json = [String : AnyObject]()
json["color"] = self.color.rgbaString()
json["title"] = self.title
json["creationDate"] = posixDateFormatter().stringFromDate(self.creationDate)
return json
}
}
If you want to play around in the Playground here is the other stuff that is referenced:
extension UIColor {
func rgbaString() -> String? {
var red: CGFloat = 0
var green: CGFloat = 0
var blue: CGFloat = 0
var alpha: CGFloat = 0
if self.getRed(&red, green: &green, blue: &blue, alpha: &alpha) {
return "\(red),\(green),\(blue),\(alpha)"
}
return nil
}
public convenience init?(rgbaString: String) {
var red: Float = 0
var green: Float = 0
var blue: Float = 0
var alpha: Float = 1
let scanner = NSScanner(string: rgbaString)
scanner.scanFloat(&red)
scanner.scanString(",", intoString: nil)
scanner.scanFloat(&green)
scanner.scanString(",", intoString: nil)
scanner.scanFloat(&blue)
scanner.scanString(",", intoString: nil)
scanner.scanFloat(&alpha)
self.init(red: CGFloat(red), green: CGFloat(green), blue: CGFloat(blue), alpha: CGFloat(alpha))
}
}
func posixDateFormatter() -> NSDateFormatter {
let posixDateFormatter = NSDateFormatter()
posixDateFormatter.locale = NSLocale(localeIdentifier:"en_US_POSIX")
posixDateFormatter.timeZone = NSTimeZone(forSecondsFromGMT: 0)
posixDateFormatter.dateFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"
return posixDateFormatter
}
let originalObject = FancyObject(title: "Object 1", color: UIColor.magentaColor())
let originalJSONDictionary = originalObject.jsonRepresentation()
var error: NSError?
let json = NSJSONSerialization.dataWithJSONObject(originalJSONDictionary, options: NSJSONWritingOptions.PrettyPrinted, error: &error)
if json == nil {
println("Can't create json \(error)")
}
/* JSON:
{
"title" : "Object 1",
"creationDate" : "2015-03-14T23:04:35Z",
"color" : "1.0,0.0,1.0,1.0"
}
*/
let dictionaryFromJSON = NSJSONSerialization.JSONObjectWithData(json!, options: nil, error: &error) as? [String : AnyObject]
if dictionaryFromJSON == nil {
println("Can't create dict \(error)")
}
let objectFromJSON = FancyObject(dictionary: dictionaryFromJSON!)

Answer 2

According to the docs the definitive way is to call isValidJSONObject: or try:
An object that may be converted to JSON must have the following
properties:
The top level object is an NSArray or NSDictionary.
All objects are instances of NSString, NSNumber, NSArray, NSDictionary, or NSNull.
All dictionary keys are instances of NSString.
Numbers are not NaN or infinity.
Other rules may apply. Calling isValidJSONObject: or attempting a
conversion are the definitive ways to tell if a given object can be
converted to JSON data.