NSCoding class chaining with Swift
While I was trying to get some Swift classes to conform to NSCoding so that I could serialize them, I found out that it can be a little annoying to get the init(coder:) calls to chain through your class hierarchy. All of the resources I found online suggested that my initializers need to be declared as convenience, however if I declared them as such, they would complain that you need to call self’s designated initializer. I could remove the convenience, but this is quite annoying because it forced me to do all of my initialization with a coder. After a little research, I discovered that I needed to remove the convenience AND make sure I also override the default init. I believe the issue is that the default init is marked as designated and forces your subclasses to call init(), if you override without required, you can call a different initializer from a subclass. Here is a short example and a Playground
class Person: NSObject, NSCoding {
var name: String = "Bob"
override init() {
super.init()
}
required init(coder aDecoder: NSCoder) {
self.name = aDecoder.decodeObjectForKey("name") as! String
}
func encodeWithCoder(aCoder: NSCoder) {
aCoder.encodeObject(self.name, forKey: "name")
}
}
class Employee: Person {
var position: String = "Manager"
override init() {
super.init()
}
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.position = aDecoder.decodeObjectForKey("position") as! String
}
override func encodeWithCoder(aCoder: NSCoder) {
super.encodeWithCoder(aCoder)
aCoder.encodeObject(self.position, forKey: "position")
}
}
var person = Employee()
person.name = "Bill"
person.position = "Worker"
print(person.name)
print(person.position)
let data = NSKeyedArchiver.archivedDataWithRootObject(person)
let newPerson = NSKeyedUnarchiver.unarchiveObjectWithData(data) as? Employee
print(person.name)
print(person.position)
This has been tested with Swift 1.2
