App crashes when trying to encode custom objects that conform to codable protocol and I can't figure out why, any thoughts?

So I have two custom objects, Exercises and Workouts. Exercises conforms to Codable and is able to be encoded and decoded just fine using JSONEncoder. I have an array of Exercise objects that I archive. The issue is with the Workout object. For some reason it does not get encoded using the JSON encoder. I am trying to encode an object which contains two arrays of Workout objects.

Any thoughts as to why this is crashing? I earlier had the manual implementation of Codable in Workout object but it would crash at this line:

let exercisesData = try NSKeyedArchiver.archivedData(withRootObject: exercises, requiringSecureCoding: true)

Then I realized all attributes of Workout already conform to Codable so I commented it out. Code is below.

With the manual implementation of Codable in the Workout object removed, the error message I get is:

>The data couldn't be written because it isn't in the correct format

(again I'm using JSONEncoder to encode an object with 2 arrays of Workout objects).
If I leave the manual implementation uncommented, it crashes at this line:

let exercisesData = try NSKeyedArchiver.archivedData(withRootObject: exercises, requiringSecureCoding: true)

with the message:

>Exercise does not implement methodSignatureForSelector -- trouble ahead Unrecognized selector Exercise replacementObjectForKeyedArchiver

I'm new to Swift programming and I was following some guides on how to set this up. It has worked for me a few weeks ago with simpler data.

class Exercise: Equatable, Codable, NSCopying {
    var name: String
    var muscleGroup: String
    var description: String
    var image: UIImage
    var logs = [(weight: String, reps: String, complete: Bool)]()
    private let isPrimary: Bool
    
    //Init function
    init(name: String, muscleGroup: String, description: String, image: UIImage, isPrimary: Bool = false) {
        self.name = name //Treat this as unique
        self.muscleGroup = muscleGroup
        self.description = description
        self.image = image
        self.isPrimary = isPrimary
    }
    
    //Override equatable to check for uniqueness
    static func == (lhs: Exercise, rhs: Exercise) -> Bool {
        return lhs.name.lowercased() == rhs.name.lowercased()
    }
    
    public enum CodingKeys: String, CodingKey {
        case name
        case muscleGroup
        case description
        case image
        case logs
        case isPrimary
    }
    
    //Decoder function implementation
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        
        // Decoding the name property
        let nameData = try container.decode(Data.self, forKey: .name)
        self.name = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(nameData) as? String ?? "No Exercise Name"

        // Decoding the muscleGroup property
        let muscleGroupData = try container.decode(Data.self, forKey: .muscleGroup)
        self.muscleGroup = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(muscleGroupData) as? String ?? "Other"

        // Decoding the description property
        let descriptionData = try container.decode(Data.self, forKey: .description)
        self.description = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(descriptionData) as? String ?? "None"
        
        // Decoding the image property
        let imageData = try container.decode(Data.self, forKey: .image)
        self.image = try (NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(imageData) as? UIImage)!
        
        // Deocding the logs property
        let logsData = try container.decode(Data.self, forKey: .logs)
        self.logs = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(logsData) as? [(weight: String, reps: String, complete: Bool)] ?? [(weight: String, reps: String, complete: Bool)]()
        
        // Deocding the primary property
        let isPrimaryData = try container.decode(Data.self, forKey: .isPrimary)
        self.isPrimary = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(isPrimaryData) as? Bool ?? false
    }

    //Encoder function implementation
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        
        // Encoding the name property
        let nameData = try NSKeyedArchiver.archivedData(withRootObject: name, requiringSecureCoding: true)
        try container.encode(nameData, forKey: .name)

        // Encoding the muscleGroup property
        let muscleGroupData = try NSKeyedArchiver.archivedData(withRootObject: muscleGroup, requiringSecureCoding: true)
        try container.encode(muscleGroupData, forKey: .muscleGroup)

        // Encoding the description property
        let descriptionData = try NSKeyedArchiver.archivedData(withRootObject: description, requiringSecureCoding: true)
        try container.encode(descriptionData, forKey: .description)
        
        // Encoding the image property
        let imageData = try NSKeyedArchiver.archivedData(withRootObject: image, requiringSecureCoding: true)
        try container.encode(imageData, forKey: .image)
        
        // Encoding the logs property
        let logsData = try NSKeyedArchiver.archivedData(withRootObject: logs, requiringSecureCoding: true)
        try container.encode(logsData, forKey: .logs)
        
        // Encoding the primary property
        let isPrimaryData = try NSKeyedArchiver.archivedData(withRootObject: isPrimary, requiringSecureCoding: true)
        try container.encode(isPrimaryData, forKey: .isPrimary)
     }
}

class Workout: Codable {
    var title: String
    var date: Date
    let duration: String //in minutes
    var exercises = [Exercise]()
    private let isPrimary: Bool
    
    //Init function
    init(title: String, date: Date, duration: String, exercises: [Exercise], isPrimary: Bool = false) {
        self.title = title
        self.date = date
        self.duration = duration
        self.exercises = exercises
        self.isPrimary = isPrimary
    }
    
    // public enum CodingKeys: String, CodingKey {
    //    case title
    //    case date
    //    case duration
    //    case exercises
    //    case isPrimary
    // }

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

    //     // Decoding the title property
    //     let titleData = try container.decode(Data.self, forKey: .title)
    //     self.title = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(titleData) as? String ?? "New Workout"

    //     // Decoding the date property
    //     let dateData = try container.decode(Data.self, forKey: .date)
    //     self.date = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(dateData) as? Date ?? Date()

    //     // Decoding the duration property
    //     let durationData = try container.decode(Data.self, forKey: .duration)
    //     self.duration = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(durationData) as? String ?? "0"

    //     //Decoding the exercises property
    //     let exercisesData = try container.decode(Data.self, forKey: .exercises)
    //     self.exercises = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(exercisesData) as? [Exercise] ?? [Exercise]()

    //     // Deocding the primary property
    //     let isPrimaryData = try container.decode(Data.self, forKey: .isPrimary)
    //     self.isPrimary = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(isPrimaryData) as? Bool ?? false
    // }

    // //Encoder function implementation
    // func encode(to encoder: Encoder) throws {
    //     var container = encoder.container(keyedBy: CodingKeys.self)

    //     // Encoding the title property
    //     let titleData = try NSKeyedArchiver.archivedData(withRootObject: title, requiringSecureCoding: true)
    //     try container.encode(titleData, forKey: .title)

    //     // Encoding the date property
    //     let dateData = try NSKeyedArchiver.archivedData(withRootObject: date, requiringSecureCoding: true)
    //     try container.encode(dateData, forKey: .date)

    //     // Encoding the duration property
    //     let durationData = try NSKeyedArchiver.archivedData(withRootObject: duration, requiringSecureCoding: true)
    //     try container.encode(durationData, forKey: .duration)

    //     // Encoding the exercises property
    //     let exercisesData = try NSKeyedArchiver.archivedData(withRootObject: exercises, requiringSecureCoding: true)
    //     try container.encode(exercisesData, forKey: .exercises)

    //     // Encoding the primary property
    //     let isPrimaryData = try NSKeyedArchiver.archivedData(withRootObject: isPrimary, requiringSecureCoding: true)
    //     try container.encode(isPrimaryData, forKey: .isPrimary)
    // }
}

There's no reason at all to be using NSKeyedArchiver in your encode and no reason to use NSKeyedUnarchiver in your init. Just use the APIs provided by Encoder and Decoder.

Here's your code all cleaned up. I replaced the tuple being used for the logs with another struct. I changed your two classes to be struct. Only the Exercise struct needs a custom init and encode since UIImage doesn't conform to Codable. The only need for the custom init with all of the properties is to support default values for some of the properties.

Note that if a struct has properties that are all Codable then the whole struct is Codable without writing any code. Same for Equatable.

struct Log: Codable {
let weight: String
let reps: String
let complete: Bool
}
struct Exercise: Equatable, Codable {
let name: String
let muscleGroup: String
let description: String
let image: UIImage
let logs: [Log]
let isPrimary: Bool
init(name: String, muscleGroup: String, description: String, image: UIImage, logs: [Log] = [], isPrimary: Bool = false) {
self.name = name
self.muscleGroup = muscleGroup
self.description = description
self.image = image
self.logs = logs
self.isPrimary = isPrimary
}
//Override equatable to check for uniqueness
static func == (lhs: Exercise, rhs: Exercise) -> Bool {
return lhs.name.lowercased() == rhs.name.lowercased()
}
public enum CodingKeys: String, CodingKey {
case name
case muscleGroup
case description
case image
case logs
case isPrimary
}
//Decoder function implementation
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
// Decoding the name property
name = try container.decode(String.self, forKey: .name)
// Decoding the muscleGroup property
muscleGroup = try container.decode(String.self, forKey: .muscleGroup)
// Decoding the description property
description = try container.decode(String.self, forKey: .description)
// Decoding the image property
let imageData = try container.decode(Data.self, forKey: .image)
image = UIImage(data: imageData)!
// Deocding the logs property
logs = try container.decode([Log].self, forKey: .logs)
// Deocding the primary property
isPrimary = try container.decode(Bool.self, forKey: .isPrimary)
}
//Encoder function implementation
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
// Encoding the name property
try container.encode(name, forKey: .name)
// Encoding the muscleGroup property
try container.encode(muscleGroup, forKey: .muscleGroup)
// Encoding the description property
try container.encode(description, forKey: .description)
// Encoding the image property
let imageData = image.pngData()
try container.encode(imageData, forKey: .image)
// Encoding the logs property
try container.encode(logs, forKey: .logs)
// Encoding the primary property
try container.encode(isPrimary, forKey: .isPrimary)
}
}
struct Workout: Codable {
let title: String
let date: Date
let duration: String //in minutes
let exercises: [Exercise]
let isPrimary: Bool
init(title: String, date: Date, duration: String, exercises: [Exercise], isPrimary: Bool = false) {
self.title = title
self.date = date
self.duration = duration
self.exercises = exercises
self.isPrimary = isPrimary
}
}