How to conform an ObservableObject to the Codable protocols?

问题

In SwiftUI beta 5, Apple introduced the @Published annotation. This annotation is currently blocking this class from conforming to the Codable protocols.

How can I conform to these protocols so I can encode and decode this class to JSON? You can ignore the image property for now.

class Meal: ObservableObject, Identifiable, Codable {

    enum CodingKeys: String, CodingKey {
        case id
        case name
        case ingredients
        case numberOfPeople
    }

    var id = Globals.generateRandomId()
    @Published var name: String = "" { didSet { isInputValid() } }
    @Published var image = Image("addImage")
    @Published var ingredients: [Ingredient] = [] { didSet { isInputValid() } }
    @Published var numberOfPeople: Int = 2
    @Published var validInput = false

    func isInputValid() {
        if name != "" && ingredients.count > 0 {
            validInput = true
        }
    }
}

回答1:

Add the init() and encode() methods to your class:

required init(from decoder: Decoder) throws {
    let values = try decoder.container(keyedBy: CodingKeys.self)

    id = try values.decode(Int.self, forKey: .id)
    name = try values.decode(String.self, forKey: .name)
    ingredients = try values.decode([Ingredient].self, forKey: .ingredients)
    numberOfPeople = try values.decode(Int.self, forKey: .numberOfPeople)
}

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(ingredients, forKey: .ingredients)
    try container.encode(numberOfPeople, forKey: .numberOfPeople)
}

回答2:

After much hacking around, I managed to add Codable directly to @Published

Just add the code below in a file and your @Published variables will be automatically Codable (provided they are based on a Codable type)

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

code here:

import Foundation
import SwiftUI

extension Published:Decodable where Value:Decodable {
    public init(from decoder: Decoder) throws {
        let decoded = try Value(from:decoder)
        self = Published(initialValue:decoded)
    }
}

extension Published:Encodable where Value:Decodable {

    public func encode(to encoder: Encoder) throws {

        let mirror = Mirror(reflecting: self)
        if let valueChild = mirror.children.first(where: { $0.label == "value"
        }) {
            if let value = valueChild.value as? Encodable {
                do {
                    try value.encode(to: encoder)
                    return
                } catch let error {
                    assertionFailure("Failed encoding: \(self) - \(error)")
                }
            }
            else {
                assertionFailure("Decodable Value not decodable. Odd \(self)")
            }
        }
        else {
            assertionFailure("Mirror Mirror on the wall - why no value y'all : \(self)")
        }
    }
}

来源：https://stackoverflow.com/questions/57444059/how-to-conform-an-observableobject-to-the-codable-protocols

标签

swift

swiftui

codable