Why does @Published removes the codable protocol conformance

Question

Created Dec ’19

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I have a simple class conforming to the codable protocol. Here is an example which is the same like in the developer documentation...

class Landmark: Codable {
    var name: String
    var foundingYear: Int
}

Because the two properties inside the class body are basic Swift types the compiler has nothing to complain.

But if I want to edit these properties using SwiftUI I must also make sure that the class conforms also to the ObservableObject protocol.

class Landmark: Codable, ObservableObject {
    @Published var name: String
    @Published var foundingYear: Int
}

Now I get an Xcode error message that type Landmark does not conform to the codable protocol anymore.

This is something I cannot understand. The property wrapper @Published should not change the type of the properties String and Int. The codable conformance should imho still be given to the class without additional lines of codes.

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Answer 1

Claude31 OP

Dec ’19

Look at detailed explanation here:

h ttps://www.hackingwithswift.com/books/ios-swiftui/adding-codable-conformance-for-published-properties

You have to declare Landmark as:

class Landmark: Codable, ObservableObject {

    enum CodingKeys: CodingKey {
        case name
        case foundingYear
    }

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        name = try container.decode(String.self, forKey: .name)
        foundingYear = try container.decode(Int.self, forKey: .foundingYear)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(name, forKey: .name)
        try container.encode(foundingYear, forKey: .foundingYear)
    }
  
    @Published var name: String = ""
    @Published var foundingYear: Int = 0
}

1

Answer 2

Claude31 OP

Jan ’20

Does it work now ?, If so, don't forget to close the thread. You could also move it to SwiftUI section.

Good continuation.

0

Answer 3

Confused Vorlon OP

Jan ’20

I figured out a way to add Codable support to @Published<Value> where Value is Codable

it has a bit of a hack to access the value of the Published struct, but it seems to work

https://blog.hobbyistsoftware.com/2020/01/adding-codeable-to-published/

0

Answer 4

Claude31 OP

Feb ’20

Reimplementing the Codable protocol works as well.

0