Saving an instance of a ViewController

Question

I have a program in which the user will enter data in one view controller and the information is calculated in another. I've gotten to the point where I can enter the data and when I segue to the SecondViewController I can access my data. But when I switch back to the first ViewController, the UITextFields are blank because the ViewController is re-instantiated.

Basically my application so far has one ViewController with two UITextfields and a SecondViewController that shows the data. I need a way to save the instance of the first ViewController when I am switching between the two.

I've tried using the answer from iOS Swift, returning to the same instance of a view controller , but yourVariable cannot be set to nil, so I got stuck there.

This is my code for segue-ing from the first ViewController to the SecondViewController

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) 
  {
  if (segue.identifier == "Show")
     {
      var destinationVC = segue.destinationViewController as! MainViewController
     }
  }

I only have a button that I press to go back to the first ViewController.

Answer 1

You can create a class to store your text file, create instance of it in appdelegate(in a global scope) and get your text data to the textfield using observer. global instance of a class may not be the best choice if your app is not as simple as you described it in which case you can use NSUsersDefault to save it as plist. I hope I helped :)

//in first view controller
@IBOutlet weak var textfield: UITextField!{
    didSet{
        textfield.text = text
    }
}
var text:String = ""{
    didSet{
        textfield?.text = text
    }
}
func override viewWillAppear(animated: Bool) {
    //set value of text from your global class instance or
    //decode it here from the archive file if you used NSUsersDefault 
    text = 
}