func == from equatable protocol does not work for custom object, swift - ios

Question

My goal is to show a user list of history logins ( such as username ) if there are any. In order to do that, I am doing
1. Create an custom object named User like below
class User: NSObject
{
var login: String
init(login: String)
{
self.login = login
}
required init(coder aDecoder: NSCoder) {
login = aDecoder.decodeObjectForKey("login") as! String
}
func encodeWithCoder(aCoder: NSCoder) {
aCoder.encodeObject(login, forKey: "login")
}
}
// This conform to make sure that I compare the `login` of 2 Users
func ==(lhs: User, rhs: User) -> Bool
{
return lhs.login == rhs.login
}
At UserManager, Im doing save and retrieve an User. Before saving, I'm doing a check if the the list of history logins contains a User, I wont add it in, otherwise.
class UserManager : NSObject
{
static let sharedInstance = UserManager()
var userDefaults = NSUserDefaults.standardUserDefaults()
func saveUser(user:User)
{
var users = retrieveAllUsers()
// Check before adding
if !(users.contains(user))
{
users.append(user)
}
let encodedData = NSKeyedArchiver.archivedDataWithRootObject(users)
userDefaults.setObject(encodedData, forKey: "users")
userDefaults.synchronize()
}
func retrieveAllUsers() -> [User]
{
guard let data = userDefaults.objectForKey("users") as? NSData else
{
return [User]()
}
let users = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! [User]
// Testing purpose
for user in users
{
print(user.login)
}
return users
}
}
At first time trying, I do
UserManager.sharedInstance.saveUser(User(login: "1234"))
Now it saves the first login. At second time, I also do
UserManager.sharedInstance.saveUser(User(login: "1234"))
UserManager still adds the second login into nsuserdefault. That means the function contains fails and it leads to
func ==(lhs: User, rhs: User) -> Bool
{
return lhs.login == rhs.login
}
does not work properly.
Does anyone know why or have any ideas about this.

Answer 1

The problem is that User derives from NSObject. This means that (as you rightly say) your == implementation is never being consulted. Swift's behavior is different for objects that derive from NSObject; it does things the Objective-C way. To implement equatability on an object that derives from NSObject, override isEqual:. That is what makes an NSObject-derived object equatable in a custom way, in both Objective-C and Swift.
Just paste this code right into your User class declaration, and contains will start working as you wish:
override func isEqual(object: AnyObject?) -> Bool {
if let other = object as? User {
if other.login == self.login {
return true
}
}
return false
}

Answer 2

What's going on?
As #matt already said, the problem is about equality.
Look
var users = [User]()
users.append(User(login: "1234"))
users.contains(User(login: "1234")) // false
Look again
var users = [User]()
let user = User(login: "1234")
users.append(user)
users.contains(user) // true <---- THIS HAS CHANGED
contains
The contains function is NOT using the logic you defined here
func ==(lhs: User, rhs: User) -> Bool {
return lhs.login == rhs.login
}
Infact it is simply comparing the memory addresses of the objects.
Solution
You can solve the issue passing your own logic to contains, just replace this
if !(users.contains(user)) {
users.append(user)
}
with this
if !(users.contains { $0.login == user.login }) {
users.append(user)
}