How do you write a JSON object encoded via Swift 4 Codable protocol to a file? Before Swift 4 I used JSONSerialization.writeJSONObject
but JSONSerialization.isValidJSONObject
now returns false
on the created data (or string). An example:
import Foundation
class Shark : Codable
{
var name:String = ""
var carnivorous:Bool = true
var numOfTeeth:Int = 0
var hobbies:[String] = []
}
class JSON
{
class func encode<T:Encodable>(_ obj:T) -> String?
{
if let encodedData = try? JSONEncoder().encode(obj)
{
return String(data: encodedData, encoding: .utf8)
}
return nil
}
class func writeToStream(data:Any, path:String) -> Bool
{
var success = false
if JSONSerialization.isValidJSONObject(data)
{
if let stream = OutputStream(toFileAtPath: "\(path)", append: false)
{
stream.open()
var error:NSError?
JSONSerialization.writeJSONObject(data, to: stream, options: [], error: &error)
stream.close()
if let error = error
{
print("Failed to write JSON data: \(error.localizedDescription)")
success = false
}
}
else
{
print("Could not open JSON file stream at \(path).")
success = false
}
}
else
{
print("Data is not a valid format for JSON serialization: \(data)")
success = false
}
return success
}
}
let shark = Shark()
shark.name = "Nancy"
shark.carnivorous = true
shark.numOfTeeth = 48
shark.hobbies = ["Dancing", "Swiming", "Eating people"]
if let jsonString = JSON.encode(shark)
{
let success = JSON.writeToStream(data: jsonString.data(using: .utf8), path: "\(NSHomeDirectory())/Documents")
}
Both of these formats are invalid for JSONSerialization.isValidJSONObject()
:
JSON.writeToStream(data: jsonString, path: "\(NSHomeDirectory())/Documents")
JSON.writeToStream(data: jsonString.data(using: .utf8), path: "\(NSHomeDirectory())/Documents")
Data is not a valid format for JSON serialization:
{"numOfTeeth":48,"hobbies":["Dancing","Swiming","Eating people"],"name":"Nancy","carnivorous":true}
Data is not a valid format for JSON serialization: Optional(99 bytes)
How do I get it passed for JSON validation and then write it to a file?
JSONSerialization. Your JSONSerialization.isValidJSONObject
usage is wrong. As the documentation states:
A Foundation object that may be converted to JSON must have the following properties:
• The top level object is anNSArray
orNSDictionary
.
• All objects are instances ofNSString
,NSNumber
,NSArray
,NSDictionary
, orNSNull
.
• All dictionary keys are instances ofNSString
.
As such, Data
or String
types aren’t valid at all ;)
Writing the encoded data. To actually write the generated Data
, use the corresponding Data.write(to: URL)
method instead. For instance:
if let encodedData = try? JSONEncoder().encode(obj) {
let path = "/path/to/obj.json"
let pathAsURL = URL(fileURLWithPath: path)
do {
try encodedData.write(to: pathAsURL)
}
catch {
print("Failed to write JSON data: \(error.localizedDescription)")
}
}
As long as the JSON data is generated by the standard JSONEncoder
no additional validation is really made necessary ;)