NSCoding and NSSecureCoding in iOS

NSCoding protocol for object serialization and archiving in iOS

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iOS Development

✍️ Note

Some codes and contents are sourced from Apple’s official documentation. This post is for personal notes where I summarize the original contents to grasp the key concepts

Reference

Archives and serializations are two ways in which you can create architecture-independent byte streams of hierarchical data. Byte streams can then be written to a file or transmitted to another process, perhaps over a network. When the byte stream is decoded, the hierarchy is regenerated. Archives provide a detailed record of a collection of interrelated objects and values. Serializations record only the simple hierarchy of property-list values
Apple

Example 1, Conforms NSCoding

			
class Person: NSObject, NSCoding {
    var name: String
    var age: Int
    var friend: Person?
    
    init(name: String, age: Int, friend: Person? = nil) {
        self.name = name
        self.age = age
        self.friend = friend
    }
    
    required convenience init?(coder: NSCoder) {
        guard let name = coder.decodeObject(forKey: "name") as? String
        else {
            return nil
        }
        let age = coder.decodeInteger(forKey: "age")
        let friend = coder.decodeObject(forKey: "friend") as? Person
        
        self.init(name: name, age: age, friend: friend)
    }
    
    func encode(with coder: NSCoder) {
        coder.encode(name, forKey: "name")
        coder.encode(age, forKey: "age")
        coder.encode(friend, forKey: "friend")
    }
}

		

			
func savePerson(_ person: Person, to path: String) {
    do {
        let data = try NSKeyedArchiver.archivedData(withRootObject: person, requiringSecureCoding: false)
        try data.write(to: URL(fileURLWithPath: path))
        print("Saved Person")
    } catch {
        print("Failed: \(error)")
    }
}
func loadPerson(from path: String) -> Person? {
    do {
        let data = try Data(contentsOf: URL(fileURLWithPath: path))
//Instead unarchiveTopLevelObjectWithData You can use unarchivedObject(ofClass:from:) when you conforms NSSecureCoding protocol
        if let loadedPerson = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) as? Person {
            return loadedPerson
        }
    } catch {
        print("Failed: \(error)")
    }
    return nil
}
let friend = Person(name: "Bob", age: 35)
let person = Person(name: "Alice", age: 30, friend: friend)
let filePath = NSTemporaryDirectory() + "person_with_friend.archive"
savePerson(person, to: filePath)
if let loadedPerson = loadPerson(from: filePath) {
    if let loadedFriend = loadedPerson.friend {
        print("Person: \(loadedPerson.name), \(loadedPerson.age)")
        print("Friend: \(loadedFriend.name), \(loadedFriend.age)")
    } else {
        print("No friends")
    }
}

		

screenshot 2024 03 16 at 10.21.56e280afpm

Example 2. Conforms NSSecureCoding

screenshot 2024 03 17 at 10.53.19e280afam

In example 1, You may see this warning. unarchiveTopLevelObjectWithData was deprecated. To resolve it, let’s conforms NSSecureCoding.

screenshot 2024 03 17 at 10.55.43e280afam

screenshot 2024 03 17 at 10.54.56e280afam

			
class Person: NSObject, NSSecureCoding {
    static var supportsSecureCoding = true
    var name: String
    var age: Int
    var friend: Person?
    
    init(name: String, age: Int, friend: Person? = nil) {
        self.name = name
        self.age = age
        self.friend = friend
    }
    
    required convenience init?(coder: NSCoder) {
        guard let name = coder.decodeObject(forKey: "name") as? String
        else {
            return nil
        }
        let age = coder.decodeInteger(forKey: "age")
        let friend = coder.decodeObject(forKey: "friend") as? Person
        
        self.init(name: name, age: age, friend: friend)
    }
    
    func encode(with coder: NSCoder) {
        coder.encode(name, forKey: "name")
        coder.encode(age, forKey: "age")
        coder.encode(friend, forKey: "friend")
    }
}

		

			
func savePerson(_ person: Person, to path: String) {
    do {
        let data = try NSKeyedArchiver.archivedData(withRootObject: person, requiringSecureCoding: true)
        try data.write(to: URL(fileURLWithPath: path))
        print("Saved Person")
    } catch {
        print("Failed: \(error)")
    }
}
func loadPerson(from path: String) -> Person? {
    do {
        let data = try Data(contentsOf: URL(fileURLWithPath: path))
        if let loadedPerson = try NSKeyedUnarchiver.unarchivedObject(ofClass: Person.self, from: data) {
            return loadedPerson
        }
    } catch {
        print("Failed: \(error)")
    }
    
    return nil
}
let friend = Person(name: "Bob", age: 35)
let person = Person(name: "Alice", age: 30, friend: friend)
let filePath = NSTemporaryDirectory() + "person_with_friend.archive"
savePerson(person, to: filePath)
if let loadedPerson = loadPerson(from: filePath) {
    if let loadedFriend = loadedPerson.friend {
        print("Person: \(loadedPerson.name), \(loadedPerson.age)")
        print("Friend: \(loadedFriend.name), \(loadedFriend.age)")
    } else {
        print("No friends")
    }
}

		

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