Crash : Convert dictionary to Json string in Swift 3 - json

Question

I'm trying to convert my swift dictionary to Json string but getting strange crash by saying
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Invalid type in JSON write (_SwiftValue)'
My code:
let jsonObject: [String: AnyObject] = [
"firstname": "aaa",
"lastname": "sss",
"email": "my_email",
"nickname": "ddd",
"password": "123",
"username": "qqq"
]
do {
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: .prettyPrinted)
// here "jsonData" is the dictionary encoded in JSON data
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
// here "decoded" is of type `Any`, decoded from JSON data
// you can now cast it with the right type
if let dictFromJSON = decoded as? [String:String] {
// use dictFromJSON
}
} catch {
print(error.localizedDescription)
}
Please help me!
Regards.

Answer 1

String is not of type AnyObject. Objects are reference types, but String in swift has value semantics. A String however, can be of type Any, so the code below works. I suggest you read up on reference types and value semantic types in Swift; its a subtle but important distinction and its also different from what you expect from most other languages, where String is often a reference type (including objective C).
let jsonObject: [String: Any] = [
"firstname": "aaa",
"lastname": "sss",
"email": "my_email",
"nickname": "ddd",
"password": "123",
"username": "qqq"
]
do {
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: .prettyPrinted)
// here "jsonData" is the dictionary encoded in JSON data
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
// here "decoded" is of type `Any`, decoded from JSON data
// you can now cast it with the right type
if let dictFromJSON = decoded as? [String:String] {
print(dictFromJSON)
}
} catch {
print(error.localizedDescription)
}