Swift Use array in Json [duplicate] - arrays

Question

This question already has an answer here:
JSON with "(" ")" brackets istead of "[" "]" [closed]
(1 answer)
Closed 5 years ago.
When I add an array in my JSON object and convert it to JSON, after printing there is parenthesis instead of curly brace.
var jsonObject : [String: Any] = [:]
var x = [1,2,3,4]
jsonObject["arr"] = x
do{
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: [])
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
print(decoded)
} ...
And the result of printing:
{
arr = (
1,
2,
3,
4
);
}
But in JSON, to show an array it uses [ instead of (.
What's wrong?

Answer 1

You are converting the dictionary(!) to JSON and then you convert it back and print it.
To print the JSON string you have to write
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject)
let jsonString = String(data: jsonData, encoding: .utf8)
print(jsonString ?? "Wrong data")

Answer 2

When you print a Swift object, Swift debugger is free to print it however it wants. It's just for convenience, there are no guarantees about the format. So, it prints arrays in parenthesis.
When you convert it to JSON, on the other hand, it creates a JSON string, and JSON has a specified format for arrays, which includes square brackets.
UPDATE: after reading the question again, it seems to me you're under the impression that you're printing a JSON representation of your object. You're not. What you do currently is you convert your Swift object to JSON, and then convert it back to a Swift object. And then you print the resulting Swift object (see paragraph 1 of my answer).
So, if your goal is to print the JSON representation, you need to convert jsonData to String (see other answers), and print that string. You shouldn't use NSJSONSerialization again for backward conversion.

Answer 3

You should use this to print your JSON.
public extension Collection {
/// Convert self to JSON String.
/// - Returns: Returns the JSON as String or empty string if error while parsing.
func json() -> String {
do {
let jsonData = try JSONSerialization.data(withJSONObject: self, options: [.prettyPrinted])
guard let jsonString = String(data: jsonData, encoding: String.Encoding.utf8) else {
print("Error creating string with data.")
return "{}"
}
return jsonString
} catch let parseError {
print("json serialization error: \(parseError)")
return "{}"
}
}
}
The conversion is correct, It's just that you are printing decoded version, which is swift dictionary, not JSON.
var jsonObject : [String: Any] = [:]
var x = [1,2,3,4]
jsonObject["arr"] = x
print(jsonObject.json())
do{
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: [])
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
print(decoded)
}
Output:-
{
"arr" : [
1,
2,
3,
4
]
}

Answer 4

I added some print clauses to you code, and pasted the console log as comments.
var jsonObject : [String: Any] = [:]
var x = [1,2,3,4]
jsonObject["arr"] = x
print(type(of: jsonObject)) // Dictionary<String, Any>
do{
let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: .prettyPrinted)
let decoded = try JSONSerialization.jsonObject(with: jsonData, options: .allowFragments)
print(type(of: decoded)) // __NSSingleEntryDictionaryI
let str = String(data: jsonData, encoding: .utf8)
print(str!) /* {
"arr" : [
1,
2,
3,
4
]
}*/
}
As you can see, the type of decoded is __NSSingleEntryDictionaryI, so its result of printing is not as what you expected, with "(" instead of "[". If you want the right representation in JSON, you should convert the jsonData to String.