Swift framework for iOS and macOS - ios

Question

currently i'm developing an app for my graduation project. The problem is, that it's not just one app, it consists of an iOS app that is made for the users and a macOS app for the "Owner". In the mac App the owner can create a file that should then be red in the iOS app.
Until now I have made a script that has all the necessary variables to transport the information, it can serialise and deserialise a file and assign it to the UI. Everything worked fine as long as I was working on the macOS app, the files can be created, deserialised and so on, however when I tried to go to the iOS app, I copied the exact same script that serves as the dataModel into the project and when I tried to deserialise a file created in the macOS file the app crashed and gave me an error saying:
cannot decode object of class (ExcursionCreator.ExcursionDataModel)
for key (root); the class may be defined in source code or a library
that is not linked'
I investigated on the error and found out that i cannot just copy the script from one project to the other, so I found a source that said that I should create a framework with just this file, however i haven't found any useful topics that talk about frameworks for cross platform.
So my question in a few words is, is it true that I have to create a framework for this purpose and if so how would I do it so it works on macOS as well on iOS. Any other advice would also be greatly appreciated. Thanks in advance Jorge. :)
Update
As asked by danielv here is my code where I store the information, it also conforms to the NSCoding protocol so i can serialise and deserialise it:
import Foundation
class ExcursionDataModel: NSObject, NSCoding {
var title: String
var imagesData = [Data]()
var thumbnailImageData: Data?
var shortText = String()
var completeText = String()
var difficulty: String = "Hard"
var duration: String = "Long"
var isFavourite: Bool = false
var type: excursionType = .other
enum excursionType: String {
case biking
case rafting
case other
}
static let possibleDifficulties = ["Hard", "Medium", "Easy"]
static let possibleDurations = ["Long", "Medium", "Short"]
init (title: String) {
self.title = title
}
override init() {
self.title = "Title"
}
struct PropertyKey {
static let titleKey = "title"
static let imagesKey = "images"
static let thumbnailImageKey = "thumbnailImage"
static let shortTextKey = "shortText"
static let completeTextKey = "completeText"
static let difficultyKey = "difficulty"
static let durationKey = "duration"
static let isFavouriteKey = "isFavourite"
static let typeKey = "type"
}
//MARK: - NSCoding
func encode(with aCoder: NSCoder) {
aCoder.encode(title, forKey: PropertyKey.titleKey)
aCoder.encode(imagesData, forKey: PropertyKey.imagesKey)
aCoder.encode(thumbnailImageData, forKey: PropertyKey.thumbnailImageKey)
aCoder.encode(shortText, forKey: PropertyKey.shortTextKey)
aCoder.encode(completeText, forKey: PropertyKey.completeTextKey)
aCoder.encode(difficulty, forKey: PropertyKey.difficultyKey)
aCoder.encode(duration, forKey: PropertyKey.durationKey)
aCoder.encode(isFavourite, forKey: PropertyKey.isFavouriteKey)
aCoder.encode(type.rawValue, forKey: PropertyKey.typeKey)
}
required convenience init?(coder aDecoder: NSCoder) {
let title = aDecoder.decodeObject(forKey: PropertyKey.titleKey) as! String
self.init(title: title)
self.imagesData = aDecoder.decodeObject(forKey: PropertyKey.imagesKey) as! [Data]
self.thumbnailImageData = aDecoder.decodeObject(forKey: PropertyKey.thumbnailImageKey) as? Data
self.shortText = aDecoder.decodeObject(forKey: PropertyKey.shortTextKey) as! String
self.completeText = aDecoder.decodeObject(forKey: PropertyKey.completeTextKey) as! String
self.difficulty = aDecoder.decodeObject(forKey: PropertyKey.difficultyKey) as! String
self.duration = aDecoder.decodeObject(forKey: PropertyKey.durationKey) as! String
self.isFavourite = aDecoder.decodeObject(forKey: PropertyKey.isFavouriteKey) as! Bool
self.type = excursionType(rawValue: aDecoder.decodeObject(forKey: PropertyKey.typeKey) as! String)!
}
}

Answer 1

From NSCoder documentation:
NSCoder operates on objects, scalars, C arrays, structures, and
strings, and on pointers to these types. It does not handle types
whose implementation varies across platforms, such as union, void *,
function pointers, and long chains of pointers. A coder object stores
object type information along with the data, so an object decoded from
a stream of bytes is normally of the same class as the object that was
originally encoded into the stream.
The class that you encoded in your MacOS app is ExcursionCreator.ExcursionDataModel. Your iOS app, however, probably has different module name, so even if you include the exact same swift class in your iOS app, the actual namespaced class name would be different, e.g ExcursionIOSApp.ExcursionDataModel.
NSCoder has no idea these are the same classes, when it tries to decode the ExcursionDataModel it doesn't find it, so you get the error.
Your options are:
Option #1
Use an open portable format for your serializations. JSON is a popular choice but there are others. This has a benefit of reusability in platforms outside of Apple's ecosystem, if you later decide to port your app to, say, Android.
There is a foundation JSON serialization support in MacOS/iOS and many open source projects that offer better/additional JSON support.
Option #2
Use a different class that shares same implementation and name across platform. For example, you could use NSDictionary as your data structure. Just be sure that everything you put there is compliant with the restrictions required by NSCoder
Option #3
Put your data class in a framework. This will force the class to have the same name when used from both projects.
To create a framework, choose a MacOS framework project when creating a new projects. Add your ExcursionDataModel to this framework.
Note that you will need to compile this framework for each platform separately. So once you have it for MacOS you will need to add additional target for it in xcode to compile it for iOS.
Then include your framework's project in each of you apps. Make sure to remove the class from your app's sources.
Check Apple's Framework Programming Guide,
Personally, I'd go with option #1 and use open and popular format and stay away from Apple's proprietary serialization.