Swift Codable protocol… encoding / decoding NSCoding classes

Question

I have the following struct…

struct Photo: Codable {

    let hasShadow: Bool
    let image: UIImage?

    enum CodingKeys: String, CodingKey {
        case `self`, hasShadow, image
    }

    init(hasShadow: Bool, image: UIImage?) {
        self.hasShadow = hasShadow
        self.image = image
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        hasShadow = try container.decode(Bool.self, forKey: .hasShadow)

        // This fails
        image = try container.decode(UIImage?.self, forKey: .image) 
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(hasShadow, forKey: .hasShadow)

        // This also fails
        try container.encode(image, forKey: .image)
    }
}

Encoding a Photo fails with …

Optional does not conform to Encodable because UIImage does not conform to Encodable

Decoding fails with…

Key not found when expecting non-optional type Optional for coding key \"image\""))

Is there a way to encode Swift objects that include NSObject subclass properties that conform to NSCoding (UIImage, UIColor, etc)?

You have to write custom encode / decode code to archive / unarchive the objects to and from `Data`. Please read [Encoding and Decoding Custom Types](https://developer.apple.com/documentation/foundation/archives_and_serialization/encoding_and_decoding_custom_types) — vadian, Jul 26 '17 at 09:16

Ashley Mills · Accepted Answer · 2018-09-13T06:51:29.367

9

Thanks to @vadian pointing me in the direction of encoding/decoding Data…

class Photo: Codable {

    let hasShadow: Bool
    let image: UIImage?

    enum CodingKeys: String, CodingKey {
        case hasShadow, imageData
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        hasShadow = try container.decode(Bool.self, forKey: .hasShadow)

        if let imageData = try container.decodeIfPresent(Data.self, forKey: .imageData) {
            image = NSKeyedUnarchiver.unarchiveObject(with: imageData) as? UIImage
        } else {
            image = nil
        }
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(hasShadow, forKey: .hasShadow)

        if let image = image {
            let imageData = NSKeyedArchiver.archivedData(withRootObject: image)
            try container.encode(imageData, forKey: .imageData)
        }
    }
}

edited Sep 13 '18 at 06:51

answered Jul 26 '17 at 09:28

Ashley Mills

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So in the end `Codable` doesn't really make anything easier, when using "custom types"? :-| – d4Rk Sep 13 '17 at 14:34
Well - it allows you to encode / decode non-`NSObject` subclasses (enums & structs) – Ashley Mills Sep 13 '17 at 15:38
@AshleyMills, I am getting this error "Type 'Photo' does not conform to protocol 'Decodable'" while copying this code in my file. – Gopal Devra Nov 25 '17 at 07:38
@GopalDevra Please ask this as another question. – Ashley Mills Dec 04 '17 at 13:15

Swift Codable protocol… encoding / decoding NSCoding classes

1 Answers1