How to conform UIImage to Codable?

Question

Swift 4 has Codable and it\'s awesome. But UIImage does not conform to it by default. How can we do that?

I tried with singleValueContainer

Answer 1

You can use very elegant solution using extension for KeyedDecodingContainer and KeyedEncodingContainer classes:

enum ImageEncodingQuality {
    case png
    case jpeg(quality: Double)
}

extension KeyedEncodingContainer {
    
    mutating func encode(_ value: UIImage,
                         forKey key: KeyedEncodingContainer.Key,
                         quality: ImageEncodingQuality = .png) throws {
        var imageData: Data!
        switch quality {
        case .png:
            imageData = value.pngData()
        case .jpeg(let quality)
            imageData = value.jpegData(compressionQuality: quality)
        }
        try encode(imageData, forKey: key)
    }
    
}

extension KeyedDecodingContainer {
    
    public func decode(_ type: UIImage.Type, forKey key: KeyedDecodingContainer.Key) throws -> UIImage {
        let imageData = try decode(Data.self, forKey: key)
        if let image = UIImage(data: imageData) {
            return image
        } else {
            throw SDKError.imageConversionError
        }
    }
    
}

Here is an usage example:

class DocumentScan: Codable {

    private enum CodingKeys: String, CodingKey {
        case scanDate
        case image
    }

    let scanDate: Date
    let image: UIImage

    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        scanDate = try container.decode(Date.self, forKey: .scanDate)
        image = try container.decode(UIImage.self, forKey: .image)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(scanDate, forKey: .scanDate)
        try container.encode(image, forKey: .image, quality: .png)
    }
}

PS: You can use such way to adopt Codable to any class type