Core Data Update in swift while selecting any row

I have got a scenario in which I have 2 VC which are -

VC1 - To enter detail & save the data. VC2 - To display the datas in a table view.

Now I want that whenever I select any particular row I would update my Database at the particular row. For that I am passing the selected managed object at that particular row for which I use the following code.

VC2 class name - ViewController

Code to fetch request -

func fetchData()
{
    let appdelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    let managedContext = appdelegate.managedObjectContext

    let fetchRequest = NSFetchRequest(entityName: "Person")

    do
    {
        people = try managedContext.executeFetchRequest(fetchRequest) as! [NSManagedObject]
        print(people)
        print("FETCHING DATA")

    }
    catch let error as NSError
    {
        print("could not fetch \(error), \(error.userInfo)")
    }

    }

Code to pass the data in selected row -

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?)
    {
        if segue.identifier == "segueupdate"
        {

            let update = segue.destinationViewController as! EnterDetailViewController
          //  var managedobject = NSManagedObject()
            let indexpath = self.tableview.indexPathForSelectedRow

            let row = indexpath?.row
          let  managedobject = people[row!]

            update.managedobjectt = managedobject

        }
    }

VC2 class name - EnterDetailViewController

class EnterDetailViewController: UIViewController {

    @IBOutlet weak var nametextfield: UITextField!
    var managedobjectt = NSManagedObject()
    override func viewDidLoad() {
        super.viewDidLoad()
        if let s = managedobjectt.valueForKey("name") as? String
        {
            nametextfield.text = s //here I show the user the existing name value
        }

    }

Now in my save function I do -

@IBAction func savedata(sender: AnyObject)
    {

    let appdelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    let managedcontext = appdelegate.managedObjectContext

    let entity = NSEntityDescription.entityForName("Person", inManagedObjectContext: managedcontext)

    let person = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: managedcontext)
    person.setValue(self.nametextfield.text, forKey: "name")

    do
    {
        try managedcontext.save()
        print("SAVED")

    }
    catch let error as NSError
    {
        print("could not save \(error), \(error.userInfo)")
    }

    self.navigationController?.popToRootViewControllerAnimated(true)

}

Here I want the compiler to check the received managed object and update any changes to the database which I am unable to do because SWIFT doesn't accept a managedobject type as condition but I was able to achieve update of database by this concept in ObjC.

And another problem is when I try to compile I get an error as -

failed to call designated initializer on NSManagedObject class 'NSManagedObject'

in the prepereforsegue() method. So how to solve the problem and perform update.

This line is wrong because you're trying to create an invalid managed object instance:

var managedobjectt = NSManagedObject()

It should be

var managedobjectt : NSManagedObject?

And when you update you aren't changing the current item if it exists, you're just always creating a new instance. You should

if let person = self.managedobjectt {
    // update (if anything other than below)
} else {
    // create new (insert and set any default values)
}

person.setValue(self.nametextfield.text, forKey: "name")

// save