Swift 2.2 singleton

Question

I am new in Swift. I am trying to parse some JSON data from web service and want a singleton class of user.But I got stuck to create the singleton. Here is my code:

import Foundation
class User {
   private var success: String
   private var userId: String
   private var name: String
   private var gender: String
   private var email: String
   private var userObject = [User]()

    class  var sharedInstane:User {
        struct Singleton {
            static var onceToken: dispatch_once_t = 0
            static var instance:User? = nil
        }
        dispatch_once(&Singleton.onceToken){
            Singleton.instance = User()
        }
        return Singleton.instance!
    }

    private init(success: String, userId: String, name: String, gender:  String, email: String)
    {
        self.success = success
        self.userId = userId
        self.name = name
        self.gender = gender
        self.email = email
    }
    convenience init(dictionary: [String:AnyObject]) {
    let success = dictionary["success"] as? String
    let userId = dictionary["userId"] as? String
    let name = dictionary["name"] as? String
    let gender = dictionary["gender"] as? String
    let email = dictionary["email"] as? String
     self.init(success: success!, userId: userId!, name: name!,  gender: gender!, email: email!, )
    }

    func callWebserviceToLoadUserInfo (url:String, param:[String:AnyObject],completeHandler:(Bool?,String) -> ())

    {
     let connection = ServerConnection()
     connection.getJSONDataForWebService(url, params: param) { (response, error) in
     // code goes here
            var responseDict = response as! [String : AnyObject]
            responseDict = responseDict["responseDict"] as! [String : AnyObject]
               if responseDict["success"] as! String == "1" {
                   for dict in responseDict {
                    let user = User(dictionary: (dict as! [String:AnyObject]))
                       self.userObject.append(user)
                }
             print("user : \(self.userObject[0].name)")
            }else{
                // error goes here
            }
        }
  }

}

Can any one please help me how should I do this code?

Answer 1

The singleton in the single line sample code.

class TheOneAndOnlyKraken {
    static let sharedInstance = TheOneAndOnlyKraken()
    private init() {} //This prevents others from using the default '()' initializer for this class.
}

For more details.

Answer 2

Using Krakendev's single-line singleton code, cited by Maheshwar, and turning your convenience init into an instance function to be called with User.sharedInstance.initialize(dictionary):

import Foundation
class User {

    // Here you declare all your properties
    // "private var" and all that jazz

    static let sharedInstance = User()

    private init() {
        // If you have something to do at the initialization stage
        // you can add it here, as long as it does not involve
        // arbitrary values that you would pass as parameters.
    }

    func initialize(dictionary: [String:AnyObject]) {
        // Transfer the values of the dictionary to each `self.property`.
        // Be careful while using `as?` as you may have to deal with    
        // optionals. No need to call `self.init` at the end, because 
        // this is now a regular `func`.
    }

    // Add the rest of your stuff here

}

One note about how you were working inside of that convenience initializer: if you do property = SomeClass.someMethod().someProperty as? SomeType, then property will be of type SomeType?, or Optional(SomeType). According to The Swift Programming Language,

The conditional form, as?, returns an optional value of the type you are trying to downcast to.

Answer 3

While User was not instantiated at least one time sharedInstance will return nil. After the first successful instantiation of the User, sharedInstance starts return it and that's became impossible to instantiate another one User as singleton pattern requires it. Consider this:

class User {

    private static var sharedUser: User?

    class var sharedInstance: User? {

        return sharedUser
    }

    private init(success: String, userId: String, name: String, gender:  String, email: String)
    {
        //User initialization code here
        User.sharedUser = self
    }

    convenience init?(dictionary: [String:AnyObject]) {

        guard User.sharedUser == nil else {
            return nil
        }

        //dictionary parsing code is here
        self.init(success: success!, userId: userId!, name: name!,  gender: gender!, email: email!)
    }
}

Client's code:

User.sharedUser
//return nil

let dict: [String:AnyObject] = ["success": "success", "userId":"userId", "name":"name", "gender":"gender","email":"email"]
User(dictionary: dict)
//creates User

User.sharedUser
//returns just created user

User(dictionary: dict)
//return nil

Answer 4

You should think about making this two classes, so that User is your model class and then create a manager to handle all the users (which seems to be your goal).

So in User remove the sharedInstane part and create a second singleton class, e.g. called UserManager, with the standard way to create a singleton in Swift. Then you can keep the way you're creating your user and in the end just assign it to the singleton:

class UserManager {
    static let sharedInstance = UserManager()

    var users = [User]()
}

// in your code:
...
for dict in responseDict {
    let user = User(dictionary: (dict as! [String:AnyObject]))
    UserManager.sharedInstance.users.append(user)
}
...