Store custom data type in #AppStorage with optional initializer? - swift

Question

I'm trying to store a custom data type into AppStorage. To do so, the model conforms to RawRepresentable (followed this tutorial). It's working fine, but when I initialize the #AppStorage variable, it requires an initial UserModel value. I want to make the variable optional, so it can be nil if the user is signed out. Is this possible?
Within a class / view, I can init like this:
#AppStorage("user_model") private(set) var user: UserModel = UserModel(id: "", name: "", email: "")
But I want to init like this:
#AppStorage("user_model") private(set) var user: UserModel?
Model:
struct UserModel: Codable {
let id: String
let name: String
let email: String
enum CodingKeys: String, CodingKey {
case id
case name
case email
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
do {
id = try String(values.decode(Int.self, forKey: .id))
} catch DecodingError.typeMismatch {
id = try String(values.decode(String.self, forKey: .id))
}
self.name = try values.decode(String.self, forKey: .name)
self.email = try values.decode(String.self, forKey: .email)
}
init(id: String, name: String, email: String) {
self.id = id
self.name = name
self.email = email
}
}
// MARK: RAW REPRESENTABLE
extension UserModel: RawRepresentable {
// RawRepresentable allows a UserModel to be store in AppStorage directly.
public init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let result = try? JSONDecoder().decode(UserModel.self, from: data)
else {
return nil
}
self = result
}
var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let result = String(data: data, encoding: .utf8)
else {
return "[]"
}
return result
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(id, forKey: .id)
try container.encode(name, forKey: .name)
try container.encode(email, forKey: .email)
}
}

Answer 1

The code below works because you added a conformance UserModel: RawRepresentable:
#AppStorage("user_model") private(set) var user: UserModel = UserModel(id: "", name: "", email: "")
You need to do the same for UserModel? if you want the following to work:
#AppStorage("user_model") private(set) var user: UserModel? = nil
Here is a possible solution:
extension Optional: RawRepresentable where Wrapped == UserModel {
public init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let result = try? JSONDecoder().decode(UserModel.self, from: data)
else {
return nil
}
self = result
}
public var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let result = String(data: data, encoding: .utf8)
else {
return "[]"
}
return result
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: UserModel.CodingKeys.self)
try container.encode(self?.id, forKey: .id)
try container.encode(self?.name, forKey: .name)
try container.encode(self?.email, forKey: .email)
}
}
Note: I reused the implementation you already had for UserModel: RawRepresentable - it might need some corrections for this case.
Also because you conform Optional: RawRepresentable you need to make
UserModel public as well.

Answer 2

A possible generic approach for any optional Codable:
extension Optional: RawRepresentable where Wrapped: Codable {
public var rawValue: String {
guard let data = try? JSONEncoder().encode(self),
let json = String(data: data, encoding: .utf8)
else {
return "{}"
}
return json
}
public init?(rawValue: String) {
guard let data = rawValue.data(using: .utf8),
let value = try? JSONDecoder().decode(Self.self, from: data)
else {
return nil
}
self = value
}
}
With that in place, any Codable can now be persisted in app storage:
#AppStorage("user_model") var user: UserModel? = nil