What is Object mapping that helping Jon parsing?

Ans. : Object mapping is convert to JSON to SomeOtherObject, BussinessModel to PersistenceModel, etc or map fields of JSON to SomeOtherObject fields.

There are many third party library available for same purpose.

1. We use mapping using init method without third party library :

struct User {

  let id: Int

  let name: String

  

  init?(dictionary: [String: Any]) {

    guard let id = dictionary["id"] as? Int else { return nil }

    guard let name = dictionary["user_name"] as? String else { return nil }

    

    self.id = id

    self.name = name

  }

}

do {

  if let userDictionary = try JSONSerialization.jsonObject(with: jsonData, options: []) as? [String: Any] {

    let user = User(dictionary: userDictionary)

    //Do something with user

  }

} catch {

  print(error)

}

2. Lyft’s Mapper Library

3. Using codable protocol  (Without third party)

4. SwiftyJson 

In today's world mostly people using 3rd option for  object mapping.

Different task available in NSURLSession

Ans : 

NSURLSession   :       The NSURLSession class and related classes provide an API for downloading data from and uploading data to endpoints indicated by URLs. Your app can also use this API to perform background downloads when your app isn’t running or, in iOS, while your app is suspended.
It is replacement of NSURLConnection from iOS 7.

Types of URL Sessions :

1. default sessions: behaviour like NSURLConnection 
2. ephemeral sessions: not cache any content to disk 
3. download sessions: store the result in file and transferring data even when app is suspended, exits or crashes

Based on above sessions, developers can schedule three types of tasks: 

1. data tasks: retrieve data to memory 
2. download tasks: download file to disk 
3. upload tasks: uploading file from disk and receiving response as data in memory 

func httpGet(request: NSURLRequest!, callback: (String, String?) -> Void) {

            var session = NSURLSession.sharedSession()

            var task = session.dataTaskWithRequest(request){

                 (data, response, error) -> Void in

                 if error != nil {

                     callback(“”, error.localizedDescription)

                 } else {

                     var result = NSString(data: data, encoding:

                                           NSASCIIStringEncoding)!

                     callback(result, nil)

                 }

            }

            task.resume()

        }

        

Which type inheritance objective c support?

Ans : Objective-C supports multi-level and hierarchical inheritance.

How many times Viewdidload and viewDidLayoutSubviews called?

Ans : 

ViewDidLoad called once only when all views are loaded.

viewDidLayoutSubviews :  Apple gave a very good explanation on this by saying that it is called to notify the view controller that its view has just laid out its subviews.

In another word, viewDidLayoutSubviews is called every time the view is updated, rotated or changed or it’s bounds change.

But know that with viewDidLayoutSubviews, it only take places after all the auto layout or auto resizing calculations on the views have been applied. Meaning the method viewDidLayoutSubviews is called every time the view size changes and the view layout has been recalculated.

Read More : AppCoda

Which method will first called if I came from back button?

Ans : 

The navigation controller sends viewWillAppear: to a view controller before putting its view on the screen, and viewDidAppear: after.

Inside viewWillAppear: and viewDidAppear:, the view controller can check self.isMovingToParentViewController.

If isMovingToParentViewController is YES, the view controller is being added to the navigation controller in the first place (presumably because it's the navigation controller's root view controller, or because it is being pushed).

If isMovingToParentViewController is NO, the view controller is already in the navigation controller's stack, and another view controller is being popped to reveal it.

How can we store object in user default?

Ans : 

Actually, you will need to archive the custom object into NSData then save it to user defaults and retrieve it from user defaults and unarchive it again. You can archive it like this

let teams = [Team(id: 1, name: "team1", shortname: "t1"), Team(id: 2, name: "team2", shortname: "t2")]

var userDefaults = UserDefaults.standard
let encodedData: Data = NSKeyedArchiver.archivedData(withRootObject: teams)
userDefaults.set(encodedData, forKey: "teams")
userDefaults.synchronize()

and unarchive it like this

let decoded  = userDefaults.data(forKey: "teams")
let decodedTeams = NSKeyedUnarchiver.unarchiveObject(with: decoded) as! [Team]

But if you just did that you will get

.Team encodeWithCoder:]: unrecognized selector sent to instance

You will have to make Team conform to NSCoding just like this

class Team: NSObject, NSCoding {
    var id: Int
    var name: String
    var shortname: String


    init(id: Int, name: String, shortname: String) {
        self.id = id
        self.name = name
        self.shortname = shortname

    }

    required convenience init(coder aDecoder: NSCoder) {
        let id = aDecoder.decodeInteger(forKey: "id")
        let name = aDecoder.decodeObject(forKey: "name") as! String
        let shortname = aDecoder.decodeObject(forKey: "shortname") as! String
        self.init(id: id, name: name, shortname: shortname)
    }

    func encode(with aCoder: NSCoder) {
        aCoder.encode(id, forKey: "id")
        aCoder.encode(name, forKey: "name")
        aCoder.encode(shortname, forKey: "shortname")
    } 

}