Swift NSCoding - How to read an encoded array - arrays

Question

I'm using Swift playground to write a parent-child relationship using NSCoding.
The relationship can be described as:
One Author can write many Books
However, it causes an error when I try to save the collection of books;
Playground execution aborted: error: Execution was interrupted,
reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0). The
process has been left at the point where it was interrupted, use
"thread return -x" to return to the state before expression
evaluation.
My Swift playground code is as follows;
// Author model
class Author: NSObject, NSCoding
{
var name: String
var books:[Book] = [Book]()
init(name:String, books:[Book]?) {
self.name = name
guard let bookList = books else {
return
}
self.books = bookList
}
required convenience init?(coder aDecoder: NSCoder) {
let name = aDecoder.decodeObject(forKey:"name") as! String
let books = aDecoder.decodeObject(forKey:"books") as! [Book]
self.init(name:name, books:books)
}
func encode(with aCoder: NSCoder) {
aCoder.encode(name, forKey:"name")
aCoder.encode(books, forKey:"books")
}
}
// Book model
class Book: NSObject, NSCoding {
var title: String
var author: Author?
init(title:String, author: Author?) {
self.title = title
self.author = author
}
public convenience required init?(coder aDecoder: NSCoder) {
let title = aDecoder.decodeObject(forKey: "title") as! String
let author = aDecoder.decodeObject(forKey: "author") as! Author
self.init(title:title, author:author)
}
func encode(with aCoder: NSCoder) {
aCoder.encode(title, forKey: "title")
aCoder.encode(author, forKey: "author")
}
}
// Create the data
var author:Author = Author(name: "Tom Clancy", books: nil)
let book0 = Book(title: "The Hunt for Red October", author: author)
let book1 = Book(title: "Red Storm Rising", author: author)
author.books.append(contentsOf: [book0, book1])
// -----------
// Save data
let manager = FileManager.default
let url = manager.urls(for: .documentDirectory, in: .userDomainMask).first! as URL
let writePath: URL = url.appendingPathComponent("archive.plist")
print("Attempting to save to: \(writePath)")
let saveData = NSMutableData()
let archiver = NSKeyedArchiver(forWritingWith: saveData)
archiver.encode(books, forKey:"books")
archiver.encode(author, forKey: "author")
//NSKeyedArchiver.archiveRootObject(books, toFile: writePath.path)
archiver.finishEncoding()
_ = saveData.write(to: writePath, atomically: true)
// -----------
// Load data
print("Attempting to load from: \(writePath)")
if FileManager.default.fileExists(atPath: writePath.path) {
if let saveData = try? Data(contentsOf: writePath) {
let unarchiver = NSKeyedUnarchiver(forReadingWith: saveData)
// Crash occurs here
var authorData = unarchiver.decodeObject(forKey: "author") as! Author
print (authorData.name)
}
} else {
print("No data archive exists")
}
So my question is: What is causing the error and how can I rectify the issue?
Many thanks

Answer 1

I was able to solve this problem by refactoring my code.
class Author: NSObject, NSCoding
{
var name: String
var books:[Book] = [Book]()
init(name:String, books:[Book]?) {
self.name = name
guard let bookList = books else {
return
}
self.books = bookList
}
required convenience init?(coder aDecoder: NSCoder) {
let name = aDecoder.decodeObject(forKey:"name") as! String
let books = aDecoder.decodeObject(forKey:"books") as! [Book]
self.init(name:name, books:books)
}
func encode(with aCoder: NSCoder) {
aCoder.encode(name, forKey:"name")
aCoder.encode(books, forKey:"books")
}
}
class Book: NSObject, NSCoding {
var title: String
var author: Author
init(title:String, author: Author) {
self.title = title
self.author = author
}
public convenience required init?(coder aDecoder: NSCoder) {
let title = aDecoder.decodeObject(forKey: "title") as! String
let author = aDecoder.decodeObject(forKey: "author") as! Author
self.init(title:title, author:author)
}
func encode(with aCoder: NSCoder) {
aCoder.encode(title, forKey: "title")
aCoder.encode(author, forKey: "author")
}
}
let author:Author = Author(name: "Tom Clancy", books: nil)
let books = [
Book(title: "The Hunt for Red October", author: author)
, Book(title: "Red Storm Rising", author: author)
]
//author.books.append(contentsOf: books)
// -----------
// Save data
let manager = FileManager.default
let url = manager.urls(for: .documentDirectory, in: .userDomainMask).first! as URL
let writeFile: URL = url.appendingPathComponent("books.data")
print ("Attempting to write to: \(writeFile.path)")
NSKeyedArchiver.archiveRootObject(books, toFile: writeFile.path)
if let bookData = NSKeyedUnarchiver.unarchiveObject(withFile: writeFile.path) as? [Book] {
for book in bookData {
print ("\(book.title) - \(book.author.name)")
}
}
This seems to work.
Issue closed