What is the problem?
Currently I am building an app-extension on my main app which communicates via a JSON. Theming and data is located in the JSON and is being parsed via the codable protocol from Apple. The problem I am experiencing right now is making NSAttributedString codable compliant. I know it is not build in but I know it can be converted to data and back to an nsattributedstring.
What I have so far?
Cast a NSAttributedString to data in order to share it via a JSON.
if let attributedText = something.attributedText {
do {
let htmlData = try attributedText.data(from: NSRange(location: 0, length: attributedText.length), documentAttributes: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType])
let htmlString = String(data: htmlData, encoding: .utf8) ?? ""
} catch {
print(error)
}
}
Cast a html JSON string back to NSAttributedString:
do {
return try NSAttributedString(data: self, options: [.documentType: NSAttributedString.DocumentType.html, .characterEncoding: String.Encoding.utf8.rawValue], documentAttributes: nil)
} catch {
print("error:", error)
return nil
}
My Question?
How to make a struct that has a property nsAttributedTitle which is of type NSAttributedString and make it codable compliant with custom encoder decoder?
Example of the struct (without thinking about codable compliance):
struct attributedTitle: Codable {
var title: NSAttributedString
enum CodingKeys: String, CodingKey {
case title
}
public func encode(to encoder: Encoder) throws {}
public init(from decoder: Decoder) throws {}
}
NSAttributedString conforms to NSCoding so you can use NSKeyedArchiver to get a Data object.
This is a possible solution
class AttributedString : Codable {
let attributedString : NSAttributedString
init(nsAttributedString : NSAttributedString) {
self.attributedString = nsAttributedString
}
public required init(from decoder: Decoder) throws {
let singleContainer = try decoder.singleValueContainer()
guard let attributedString = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(singleContainer.decode(Data.self)) as? NSAttributedString else {
throw DecodingError.dataCorruptedError(in: singleContainer, debugDescription: "Data is corrupted")
}
self.attributedString = attributedString
}
public func encode(to encoder: Encoder) throws {
var singleContainer = encoder.singleValueContainer()
try singleContainer.encode(NSKeyedArchiver.archivedData(withRootObject: attributedString, requiringSecureCoding: false))
}
}
Update:
In Swift 5.5 native AttributedString has been introduced which conforms to Codable.
Related
I have such field in my json response:
"title": [2402, "Dr.", "Prof.", "Prof. Dr.", "HM"]
And I would like to parse it. I have my model class:
struct AppDataModel:Decodable {
...
let title = Dictionary<String,Any>()
enum CodingKeys: String,CodingKey{
case title
...
}
...
}
As you can see I tried to use Dictionary<String,Any>() for it. And also I thought about array of Any -> [Any] but I usually get such error:
Type 'AppDataModel' does not conform to protocol 'Decodable'
I think that I have to process it like an ordinary json. But I didn't find such data type in Swift, only dictionary. So, maybe someone knows how to process such response fields?
This is an example to decode a single key as heterogenous array
let jsonString = """
{"title": [2402, "Dr.", "Prof.", "Prof. Dr.", "HM"], "name":"Foo"}
"""
struct AppDataModel : Decodable {
let titles : [String]
let name : String
private enum CodingKeys: String, CodingKey { case title, name }
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
var titlesContainer = try container.nestedUnkeyedContainer(forKey: .title)
var titleArray = [String]()
let _ = try titlesContainer.decode(Int.self) // decode and drop the leading integer
while !titlesContainer.isAtEnd { // decode all following strings
titleArray.append(try titlesContainer.decode(String.self))
}
titles = titleArray
self.name = try container.decode(String.self, forKey: .name)
}
}
let data = Data(jsonString.utf8)
do {
let result = try JSONDecoder().decode(AppDataModel.self, from: data)
print(result)
} catch {
print(error)
}
struct AppDataModel: Codable {
let title: [Title]?
}
extension AppDataModel {
init(data: Data) throws {
self = try newJSONDecoder().decode(AppDataModel.self, from: data)
}
init(_ json: String, using encoding: String.Encoding = .utf8) throws {
guard let data = json.data(using: encoding) else {
throw NSError(domain: "JSONDecoding", code: 0, userInfo: nil)
}
try self.init(data: data)
}
init(fromURL url: URL) throws {
try self.init(data: try Data(contentsOf: url))
}
func with(
title: [Title]?? = nil
) -> AppDataModel {
return AppDataModel(
title: title ?? self.title
)
}
func jsonData() throws -> Data {
return try newJSONEncoder().encode(self)
}
func jsonString(encoding: String.Encoding = .utf8) throws -> String? {
return String(data: try self.jsonData(), encoding: encoding)
}
}
enum Title: Codable {
case integer(Int)
case string(String)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let x = try? container.decode(Int.self) {
self = .integer(x)
return
}
if let x = try? container.decode(String.self) {
self = .string(x)
return
}
throw DecodingError.typeMismatch(Title.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for Title"))
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .integer(let x):
try container.encode(x)
case .string(let x):
try container.encode(x)
}
}
}
func newJSONDecoder() -> JSONDecoder {
let decoder = JSONDecoder()
if #available(iOS 10.0, OSX 10.12, tvOS 10.0, watchOS 3.0, *) {
decoder.dateDecodingStrategy = .iso8601
}
return decoder
}
func newJSONEncoder() -> JSONEncoder {
let encoder = JSONEncoder()
if #available(iOS 10.0, OSX 10.12, tvOS 10.0, watchOS 3.0, *) {
encoder.dateEncodingStrategy = .iso8601
}
return encoder
}
//use
do {
let appDataModel = try AppDataModel(json)
}
catch{
//handle error
}
I am attempting to decode a JSON response from a third-party API which contains nested/child JSON that has been base64 encoded.
Contrived Example JSON
{
"id": 1234,
"attributes": "eyAibmFtZSI6ICJzb21lLXZhbHVlIiB9",
}
PS "eyAibmFtZSI6ICJzb21lLXZhbHVlIiB9" is { 'name': 'some-value' } base64 encoded.
I have some code that is able to decode this at present but unfortunately I have to reinstanciate an additional JSONDecoder() inside of the init in order to do so, and this is not cool...
Contrived Example Code
struct Attributes: Decodable {
let name: String
}
struct Model: Decodable {
let id: Int64
let attributes: Attributes
private enum CodingKeys: String, CodingKey {
case id
case attributes
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.id = try container.decode(Int64.self, forKey: .id)
let encodedAttributesString = try container.decode(String.self, forKey: .attributes)
guard let attributesData = Data(base64Encoded: encodedAttributesString) else {
fatalError()
}
// HERE IS WHERE I NEED HELP
self.attributes = try JSONDecoder().decode(Attributes.self, from: attributesData)
}
}
Is there anyway to achieve the decoding without instanciating the additional JSONDecoder?
PS: I have no control over the response format and it cannot be changed.
If attributes contains only one key value pair this is the simple solution.
It decodes the base64 encoded string directly as Data – this is possible with the .base64 data decoding strategy – and deserializes it with traditional JSONSerialization. The value is assigned to a member name in the Model struct.
If the base64 encoded string cannot be decoded a DecodingError will be thrown
let jsonString = """
{
"id": 1234,
"attributes": "eyAibmFtZSI6ICJzb21lLXZhbHVlIiB9",
}
"""
struct Model: Decodable {
let id: Int64
let name: String
private enum CodingKeys: String, CodingKey {
case id, attributes
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.id = try container.decode(Int64.self, forKey: .id)
let attributeData = try container.decode(Data.self, forKey: .attributes)
guard let attributes = try JSONSerialization.jsonObject(with: attributeData) as? [String:String],
let attributeName = attributes["name"] else { throw DecodingError.dataCorruptedError(forKey: .attributes, in: container, debugDescription: "Attributes isn't eiter a dicionary or has no key name") }
self.name = attributeName
}
}
let data = Data(jsonString.utf8)
do {
let decoder = JSONDecoder()
decoder.dataDecodingStrategy = .base64
let result = try decoder.decode(Model.self, from: data)
print(result)
} catch {
print(error)
}
I find the question interesting, so here is a possible solution which would be to give the main decoder an additional one in its userInfo:
extension CodingUserInfoKey {
static let additionalDecoder = CodingUserInfoKey(rawValue: "AdditionalDecoder")!
}
var decoder = JSONDecoder()
let additionalDecoder = JSONDecoder() //here you can put the same one, you can add different options, same ones, etc.
decoder.userInfo = [CodingUserInfoKey.additionalDecoder: additionalDecoder]
Because the main method we use from JSONDecoder() is func decode<T>(_ type: T.Type, from data: Data) throws -> T where T : Decodable and I wanted to keep it as such, I created a protocol:
protocol BasicDecoder {
func decode<T>(_ type: T.Type, from data: Data) throws -> T where T : Decodable
}
extension JSONDecoder: BasicDecoder {}
And I made JSONDecoder respects it (and since it already does...)
Now, to play a little and check what could be done, I created a custom one, in the idea of having like you said a XML Decoder, it's basic, and it's just for the fun (ie: do no replicate this at home ^^):
struct CustomWithJSONSerialization: BasicDecoder {
func decode<T>(_ type: T.Type, from data: Data) throws -> T where T : Decodable {
guard let dict = try JSONSerialization.jsonObject(with: data) as? [String: Any] else { fatalError() }
return Attributes(name: dict["name"] as! String) as! T
}
}
So, init(from:):
guard let attributesData = Data(base64Encoded: encodedAttributesString) else { fatalError() }
guard let additionalDecoder = decoder.userInfo[.additionalDecoder] as? BasicDecoder else { fatalError() }
self.attributes = try additionalDecoder.decode(Attributes.self, from: attributesData)
Let's try it now!
var decoder = JSONDecoder()
let additionalDecoder = JSONDecoder()
decoder.userInfo = [CodingUserInfoKey.additionalDecoder: additionalDecoder]
var decoder2 = JSONDecoder()
let additionalDecoder2 = CustomWithJSONSerialization()
decoder2.userInfo = [CodingUserInfoKey.additionalDecoder: additionalDecoder]
let jsonStr = """
{
"id": 1234,
"attributes": "eyAibmFtZSI6ICJzb21lLXZhbHVlIiB9",
}
"""
let jsonData = jsonStr.data(using: .utf8)!
do {
let value = try decoder.decode(Model.self, from: jsonData)
print("1: \(value)")
let value2 = try decoder2.decode(Model.self, from: jsonData)
print("2: \(value2)")
}
catch {
print("Error: \(error)")
}
Output:
$> 1: Model(id: 1234, attributes: Quick.Attributes(name: "some-value"))
$> 2: Model(id: 1234, attributes: Quick.Attributes(name: "some-value"))
After reading this interesting post, I came up with a reusable solution.
You can create a new NestedJSONDecodable protocol which gets also the JSONDecoder in it's initializer:
protocol NestedJSONDecodable: Decodable {
init(from decoder: Decoder, using nestedDecoder: JSONDecoder) throws
}
Implement the decoder extraction technique (from the aforementioned post) together with a new decode(_:from:) function for decoding NestedJSONDecodable types:
protocol DecoderExtractable {
func decoder(for data: Data) throws -> Decoder
}
extension JSONDecoder: DecoderExtractable {
struct DecoderExtractor: Decodable {
let decoder: Decoder
init(from decoder: Decoder) throws {
self.decoder = decoder
}
}
func decoder(for data: Data) throws -> Decoder {
return try decode(DecoderExtractor.self, from: data).decoder
}
func decode<T: NestedJSONDecodable>(_ type: T.Type, from data: Data) throws -> T {
return try T(from: try decoder(for: data), using: self)
}
}
And change your Model struct to conform to NestedJSONDecodable protocol instead of Decodable:
struct Model: NestedJSONDecodable {
let id: Int64
let attributes: Attributes
private enum CodingKeys: String, CodingKey {
case id
case attributes
}
init(from decoder: Decoder, using nestedDecoder: JSONDecoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.id = try container.decode(Int64.self, forKey: .id)
let attributesData = try container.decode(Data.self, forKey: .attributes)
self.attributes = try nestedDecoder.decode(Attributes.self, from: attributesData)
}
}
The rest of your code will remain the same.
You could create a single decoder as a static property of Model, configure it once, and use it for all your Model decoding needs, both externally and internally.
Unsolicited thought:
Honestly, I would only recommend doing that if you're seeing a measurable loss of CPU time or crazy heap growth from the allocation of additional JSONDecoders… they're not heavyweight objects, less than 128 bytes unless there's some trickery I don't understand (which is pretty common though tbh):
let decoder = JSONDecoder()
malloc_size(Unmanaged.passRetained(decoder).toOpaque()) // 128
func encode(to encoder: Encoder) throws is required for the Codable protocol.
Is there any reason to implement this in your code for an NSManagedObject subclass?
Is there something I'm missing, or should a fatal error simply be returned from this function.
The example subclass is the same for all such subclasses
#objc(Commit)
public class Commit: NSManagedObject, Codable {
public func encode(to encoder: Encoder) throws {
// Note encode is blank here
}
required convenience public init(from decoder: Decoder) throws {
// return the context from the decoder userinfo dictionary
guard let contextUserInfoKey = CodingUserInfoKey.context,
let managedObjectContext = decoder.userInfo[contextUserInfoKey] as? NSManagedObjectContext,
let entity = NSEntityDescription.entity(forEntityName: "Commit", in: managedObjectContext)
else {
fatalError("decode failure")
}
// Super init of the NSManagedObject
self.init(entity: entity, insertInto: managedObjectContext)
let values = try decoder.container(keyedBy: CodingKeys.self)
do {
sha = try values.decode(String.self, forKey: .sha)
url = try values.decode(String.self, forKey: .url)
html_url = try values.decode(String.self, forKey: .html_url)
gitcommit = try values.decode(GitCommit.self, forKey: .gitcommit)
} catch {
print ("error")
}
}
enum CodingKeys: String, CodingKey {
case sha = "sha"
case gitcommit = "commit"
case url = "url"
case html_url = "html_url"
}
}
Adopting Codable implies that you want to decode and encode the objects.
If you have no reason to encode the class adopt only Decodable
I need write and read NSAttributedString data into a json file, using this previously answered question I can encode the it but it throws an error while decoding.
class AttributedString : Codable {
let attributedString : NSAttributedString
init(attributedString : NSAttributedString) {
self.attributedString = attributedString
}
public required init(from decoder: Decoder) throws {
let singleContainer = try decoder.singleValueContainer()
let base64String = try singleContainer.decode(String.self)
guard let data = Data(base64Encoded: base64String) else { throw DecodingError.dataCorruptedError(in: singleContainer, debugDescription: "String is not a base64 encoded string") }
guard let attributedString = try NSKeyedUnarchiver.unarchivedObject(ofClasses: [NSAttributedString.self], from: data) as? NSAttributedString else { throw DecodingError.dataCorruptedError(in: singleContainer, debugDescription: "Data is not NSAttributedString") }
self.attributedString = attributedString
}
func encode(to encoder: Encoder) throws {
let data = try NSKeyedArchiver.archivedData(withRootObject: attributedString, requiringSecureCoding: false)
var singleContainer = encoder.singleValueContainer()
try singleContainer.encode(data.base64EncodedString())
}
}
And:
do {
let jsonEncoder = JSONEncoder()
let jsonData = try jsonEncoder.encode(attributedString)
let jsonString = String(data: jsonData, encoding: .utf8)
print("***\n\(String(describing: jsonString))\n***") // It works
let jsonDecoder = JSONDecoder()
let attrib = try jsonDecoder.decode(AttributedString.self, from: jsonData)
print(attrib.attributedString.string)
}catch{
print(error) // throws error
}
Error Domain=NSCocoaErrorDomain Code=4864 "value for key 'NS.objects'
was of unexpected class 'NSShadow'. Allowed classes are '{(
NSGlyphInfo,
UIColor,
NSDictionary,
UIFont,
NSURL,
NSParagraphStyle,
NSString,
NSAttributedString,
NSArray,
NSNumber )}'." UserInfo={NSDebugDescription=value for key 'NS.objects' was of unexpected class 'NSShadow'. Allowed classes are
'{(
NSGlyphInfo,
UIColor,
NSDictionary,
UIFont,
NSURL,
NSParagraphStyle,
NSString,
NSAttributedString,
NSArray,
NSNumber )}'.}
PS: I need to keep attributes
You can try unarchiveTopLevelObjectWithData to unarchive your AttributedString object data:
NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data)
Your AttributedString implemented as a struct should look something like this:
struct AttributedString {
let attributedString: NSAttributedString
init(attributedString: NSAttributedString) { self.attributedString = attributedString }
init(string str: String, attributes attrs: [NSAttributedString.Key: Any]? = nil) { attributedString = .init(string: str, attributes: attrs) }
}
Archiving / Encoding
extension NSAttributedString {
func data() throws -> Data { try NSKeyedArchiver.archivedData(withRootObject: self, requiringSecureCoding: false) }
}
extension AttributedString: Encodable {
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(attributedString.data())
}
}
Unarchiving / Decoding
extension Data {
func topLevelObject() throws -> Any? { try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(self) }
func unarchive<T>() throws -> T? { try topLevelObject() as? T }
func attributedString() throws -> NSAttributedString? { try unarchive() }
}
extension AttributedString: Decodable {
public init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
guard let attributedString = try container.decode(Data.self).attributedString() else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "Corrupted Data")
}
self.attributedString = attributedString
}
}
Before you answer:
I'm aware:
That an empty string is an invalid URL
That I could write a custom decoder for Employee
That I could declare url as a String
What I'm looking for is a better solution for decoding the optional URL itself. I'm hoping there's some Codable magic I'm missing!
So, I have JSON such as
let json = Data("""
{
"name": "Fred",
"url": ""
}
""".utf8)
and a corresponding object that contains an optional URL…
struct Employee: Decodable {
let name: String
let url: URL?
}
As url in the JSON is invalid, I'd like it to decode as nil, rather than throwing an error.
Trying the following doesn't work (it doesn't get called)…
extension Optional where Wrapped == URL {
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
self = try container.decode(URL.self)
} catch {
self = nil
}
}
}
In the past I've used…
struct FailableDecodable<T: Decodable>: Deodable {
let wrapped: T?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
do {
self.wrapped = try container.decode(T.self)
} catch {
print("Error decoding failable object: \(error)")
self.wrapped = nil
}
}
}
struct Employee: Decodable {
let name: String
let url: FailableDecodable<URL>?
}
but this requires me to continually refer to url.wrapped.
Is there a better solution?
If you are using Swift 5.1, you can use #propertyWrapper:
let json = """
{
"name": "Fred",
"url": ""
}
""".data(using: .utf8)!
#propertyWrapper
struct FailableDecodable<Wrapped: Decodable>: Decodable {
var wrappedValue: Wrapped?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
wrappedValue = try? container.decode(Wrapped.self)
}
}
struct Employee: Decodable {
let name: String
#FailableDecodable
private(set) var url: URL?
}
let employee = try! JSONDecoder().decode(Employee.self, from: json)
employee.url // nil
Edit — Codable version
If you need the top level struct to be Encodable as well you can use Codable conformance to the property wrapper.
#propertyWrapper
struct FailableDecodable<Wrapped: Codable>: Codable {
var wrappedValue: Wrapped?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
wrappedValue = try? container.decode(Wrapped.self)
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(wrappedValue)
}
}
If url is nil this will output a JSON with url: null
{"name":"Fred","url":null}
If you wish to don't output the url property when nil you will need to implement a custom encoding (with encode(to:)) in Employee (which would mitigate the benefit of using a property wrapper).
Note: Using the default implementation of encode(to:) (not implementing it) works, but output an empty object when url is nil:
{"name":"Fred","url":{}}
If you get Return from initializer without initializing all stored properties warning for your Codable struct initializer that contains #FailableDecodable below will resolve it.
#propertyWrapper
struct FailableDecodable<Wrapped: Codable>: Codable {
var wrappedValue: Wrapped?
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
wrappedValue = try? container.decode(Wrapped.self)
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
try container.encode(wrappedValue)
}
init() {
self.wrappedValue = nil
}
}