Can't get NSKeyedArchiver to work: unrecognized selector [closed] - swift

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In a UITableView when deleting a row and saving the data source I also want to save to persistent storage.
I'm using NSKeyedArchiver to save an array of my custom object type Participant and it fails straight away with:
2018-02-13 23:01:41.818945+0000 ProjectName[28680:5720571]
-[_SwiftValue encodeWithCoder:]: unrecognized selector sent to instance 0x60800004d290
2018-02-13 23:01:41.826553+0000 ProjectName[28680:5720571] *** Terminating app due to uncaught
exception 'NSInvalidArgumentException', reason: '-[_SwiftValue
encodeWithCoder:]: unrecognized selector sent to instance
0x60800004d290'
I've searched everywhere and can't find anything that's applicable to me. So far as I can tell my data class for Participant object conforms to NSObject and NSCoding with the necessary methods implemented.
EDIT: Thank you all for your feedback so quickly. Code is below and as I said before, if I've neglected to post something necessary that likely speaks to my experience so any help gratefully received!
Data Class (excerpt)
class Participant: NSObject, NSCoding {
//MARK: Properties
var name: String
var jobTitle: String?
var picture: UIImage?
var rate: Float
var ratePeriod: ratePeriods
//MARK: Archiving Paths
static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
static let ArchiveURL = DocumentsDirectory.appendingPathComponent("participants")
//MARK: Types
struct PropertyKey {
//THESE MUST NOT CHANGE ONCE BUILT
static let name = "name"
static let jobTitle = "jobTitle"
static let picture = "picture"
static let rate = "rate"
static let ratePeriod = "ratePeriod"
}
//MARK: Initialisation
init?(name: String, jobTitle: String?, picture: UIImage?, rate: Float?, ratePeriod: ratePeriods?) {
//The name must not be empty
guard !name.isEmpty else {
return nil
}
//Init stored properties
self.name = name
self.jobTitle = jobTitle ?? ""
self.picture = picture
self.rate = rate ?? 0.0
self.ratePeriod = ratePeriod ?? .annually
}
//MARK: NSCoding
func encode(with aCoder: NSCoder) {
aCoder.encode(name, forKey: PropertyKey.name)
aCoder.encode(jobTitle, forKey: PropertyKey.jobTitle)
aCoder.encode(picture, forKey: PropertyKey.picture)
aCoder.encode(rate, forKey: PropertyKey.rate)
aCoder.encode(ratePeriod, forKey: PropertyKey.ratePeriod)
}
required convenience init?(coder aDecoder: NSCoder) {
//The name is required. If we cannot decode a name string, the init should fail.
guard let name = aDecoder.decodeObject(forKey: PropertyKey.name) as? String else {
return nil
}
let jobTitle = aDecoder.decodeObject(forKey: PropertyKey.jobTitle) as? String
let picture = aDecoder.decodeObject(forKey: PropertyKey.picture) as? UIImage
let rate = aDecoder.decodeFloat(forKey: PropertyKey.rate)
let ratePeriod = aDecoder.decodeObject(forKey: PropertyKey.ratePeriod) as? ratePeriods
//Must call designated init
self.init(name: name, jobTitle: jobTitle, picture: picture, rate: rate, ratePeriod: ratePeriod)
}
}
From inside Private Func where I'm trying to make use of it and it breaks
let archivePath = Participant.ArchiveURL.path
let isSuccessfulSave = NSKeyedArchiver.archiveRootObject(participants, toFile: archivePath)
Thank you again for any help I can get on this.
EDIT 2: I've done a bit more debugging and I guess my inexperience with the Xcode IDE and debugging has hindered this but it looks to be the ratePeriod property of the object being stored that's throwing the error. This property is a Struct which I think somebody else leaned to as being an issue. Is this resolvable or do I need to look at a different method for persisting storage of Structs?
EDIT 3: I've solved the problem but don't know how to mark this as resolved. The issue wasn't the Struct (which I wasn't storing) but rather an Enum. When using NSKeyedArchiver and NSCoding to store Enums you need to store the .rawValue and reconstitute it as an Int. ie: -
Encoding
aCoder.encode(ratePeriod.rawValue, forKey: PropertyKey.ratePeriod)
and
Decoding
let ratePeriodIntValue = (aDecoder.decodeObject(forKey: PropertyKey.ratePeriod) as? Int) ?? ratePeriods.annually.rawValue
let ratePeriod = ratePeriods(rawValue: ratePeriodIntValue)

Answer 1

Your custom object type, Participant, needs to be a class (not a struct), and in particular it must be a subclass of NSObject. Now you can adopt NSCoding successfully.

Answer 2

There is a very simple article on NSHipster about how to make your custom classes NSCoding/NSKeyedArchiver compliant. I recommend giving that a look.
As a basic answer, in order to make your object work with NSKeyedArchiver you need to tell the coder/decoder how to encode/decode your object. For example, if this is your class:
class Participant {
let name: String
let id: String
let age: Int
init(name: String, id: String, age: Int) {
self.name = name
self.id = id
self.age = age
}
}
You would need to make the following modifications to make it work with NSKeyedArchiver. First, declare that you are conforming to NSObject and NSCoding protocols. Then implement the encode methods and the convenience init?(coder:_) initializer:
class Participant: NSObject, NSCoding {
let name: String
let id: String
let age: Int
init(name: String, id: String, age: Int) {
self.name = name
self.id = id
self.age = age
}
required convenience init?(coder aDecoder: NSCoder) {
guard let name = aDecoder.decodeObject(forKey: "name") as? String,
let id = aDecoder.decodeObject(forKey: "id") as? String,
let age = aDecoder.decodeObject(forKey: "age") as? Int else { return nil }
self.init(name: name, id: id, age: age)
}
func encode(with aCoder: NSCoder) {
aCoder.encode(self.name, forKey: "name")
aCoder.encode(self.id, forKey: "id")
aCoder.encode(self.age, forKey: "age")
}
}

Answer 3

Try adding #objc to your swift equivalent encodeWithCoder: method. Ditto for the decode init method. I doubt it's the solution but might be.
Also, please show how you wrote the NSCoding methods in Swift. Maybe they don't match up, given the inherent conversion between Swift and ObjC for how they are to be written?
func encode(with aCoder: NSCoder) {