Question 66680 in IOS Swift Question posted in
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Encode AttributedString with custom attributes to JSON – Ios swift

Swift 5.5 introduced AttributedString conforming to Codable however this is not working for me as I’d expect.

Take the following example:

Here I define a custom attribute TextCase

public enum TextCase: Codable {
    case lowercase
    case uppercase
}

public struct TextCaseAttribute: CodableAttributedStringKey {
    public typealias Value = TextCase
    public static var name = "TextCaseAttribute"
}

public extension AttributeScopes {
    struct ExtendedTextAttributes: AttributeScope {
        public let textCase: TextCaseAttribute
        public let foundation: FoundationAttributes
    }
    var customAttributes: ExtendedTextAttributes.Type { ExtendedTextAttributes.self }
}

public extension AttributeDynamicLookup {
    subscript<T: AttributedStringKey>(
        dynamicMember keyPath: KeyPath<AttributeScopes.ExtendedTextAttributes, T>
    ) -> T {
        get { self[T.self] }
    }
}

and use it like this:

    var hello: AttributedString {
        var result = AttributedString("Hello")
        result.textCase = .uppercase
        result.font = .largeTitle
        return result
    }

when I use JSONEncoder to encode the AttributedString it gives me the following:

po String(decoding: JSONEncoder().encode(hello), as: UTF8.self)
->
"["Hello",{"SwiftUI.Font":{}}]"

Notice that my textCase is missing plus I expected SwiftUI.Font to have a value.

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    Implementing custom encoding and decoding seems to work:

    struct NonCodableType: Hashable {
    var inner: String
}

extension AttributeScopes {
    enum CustomCodableAttribute: CodableAttributedStringKey {
        typealias Value = NonCodableType
        static let name = "NonCodableConvertible"

        static func encode(_ value: NonCodableType, to encoder: Encoder) throws {
            var c = encoder.singleValueContainer()
            try c.encode(value.inner)
        }

        static func decode(from decoder: Decoder) throws -> NonCodableType {
            let c = try decoder.singleValueContainer()
            let inner = try c.decode(String.self)
            return NonCodableType(inner: inner)
        }
    }
}

extension AttributeDynamicLookup {
    subscript<T: AttributedStringKey>(
        dynamicMember keyPath: KeyPath<AttributeScopes.CustomCodableAttribute, T>
    ) -> T {
        self[T.self]
    }
}

struct UnifiedAttributes: AttributeScope {
    var customCodable: AttributeScopes.CustomCodableAttribute
}

struct CodableType: Codable {
    @CodableConfiguration(from: UnifiedAttributes.self)
    var attributedString = AttributedString()
}

    print it like this

    po String(decoding: JSONEncoder().encode(CodableType(attributedString: hello)), as: UTF8.self)

    Source: Apple swift-corelibs-foundation test code here https://github.com/apple/swift-corelibs-foundation/blob/main/Tests/Foundation/Tests/TestAttributedString.swift

    still curious why encoding a Codable type won't work.


  2. 0

    This solution is for NSAttributedString but you can convert it to AttributedString with init function:
    https://developer.apple.com/forums/thread/682431

    You can packing the NSAttributedString in a Codable container, and the container is Data: you can convert the NSAttributedString to Data. Because Data is codable so your custom Struct will able to be codable:

    Code to convert NSAttributedString to Data:

    extension NSAttributedString {
   
    func data() throws -> Data { try 
    NSKeyedArchiver.archivedData(withRootObject: self, requiringSecureCoding: false) }

}

    Code to convert Data back to NSAttributedString:

    extension Data {
    func topLevelObject() throws -> Any? { try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(self) }
    func unarchive<T>() throws -> T? { try topLevelObject() as? T }
    func attributedString() throws -> NSAttributedString? { try unarchive() }
}

    Add it to your custom Struct and make the whole struct Codable:

    struct CustomStruct : Codable {
    
    /// NSAttributedString in Data
    var attStringData : Data
}

    Pack it in a computedVariable for better syntax:

    extension CustomStruct {
    var string : NSAttributedString? {
        get {
            return attStringData.attributedString()
        }
        set {
            let attData =  newValue.data()
            attStringData = attData
        }
    }
}
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