EDIT - 10/31/2017: This answer mostly applies to Swift 3 and possibly earlier versions. As of late 2017, we now have Swift 4 and you should be using the Encodable and Decodable protocols to convert data between representations including JSON and file encodings. (You can add the Codable protocol to use both encoding and decoding)
The usual solution for working with JSON in Swift is to use dictionaries. So you could do:
extension Date {
var dataDictionary {
return [
"year": self.year,
"month": self.month,
"day": self.day
];
}
}
extension Lad {
var dataDictionary {
return [
"firstName": self.firstName,
"lastName": self.lastName,
"dateOfBirth": self.dateOfBirth.dataDictionary
];
}
}
and then serialize the dictionary-formatted data using JSONSerialization.
//someLad is a Lad object
do {
// encoding dictionary data to JSON
let jsonData = try JSONSerialization.data(withJSONObject: someLad.dataDictionary,
options: .prettyPrinted)
// decoding JSON to Swift object
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
// after decoding, "decoded" is of type `Any?`, so it can't be used
// we must check for nil and cast it to the right type
if let dataFromJSON = decoded as? [String: Any] {
// use dataFromJSON
}
} catch {
// handle conversion errors
}
If you just need to do this for few classes, providing methods to turn them into dictionaries is the most readable option and won't make your app noticeably larger.
However, if you need to turn a lot of different classes into JSON it would be tedious to write out how to turn each class into a dictionary. So it would be useful to use some sort of reflection API in order to be able to list out the properties of an object. The most stable option seems to be EVReflection. Using EVReflection, for each class we want to turn into json we can do:
extension SomeClass: EVReflectable { }
let someObject: SomeClass = SomeClass();
let someObjectDictionary = someObject.toDictionary();
and then, just like before, we can serialize the dictionary we just obtained to JSON using JSONSerialization. We'll just need to use object.toDictionary() instead of object.dataDictionary.
If you don't want to use EVReflection, you can implement reflection (the ability to see which fields an object has and iterate over them) yourself by using the Mirror class. There's an explanation of how to use Mirror for this purpose here.
So, having defined either a .dataDictionary computed variable or using EVReflection's .toDictionary() method, we can do
class ApiService {
func postDataToTheServer(lad: Lad) {
//if using a custom method
let dict = lad.dataDictionary
//if using EVReflection
let dict = lad.toDictionary()
//now, we turn it into JSON
do {
let jsonData = try JSONSerialization.data(withJSONObject: dict,
options: .prettyPrinted)
// send jsonData to server
} catch {
// handle errors
}
}
}
