title: Retaining Data in a View Controller When Switching from One VC to Another
body: <p>I have three views, each with its own view controller:  VC1, VC2, VC3.
  The user will frequently switch back and forth between each of the three views, both forward and backward.
  Each view contains data: both shared from the previous view and data unique to that view.
  When the user goes back to a View that he has already visited, the data displayed on that view needs to be retained (the same data as he saw the last time he visited that view), and not set to the default values the first time he visited the view. </p>
  
  <p>In the first view controller, VC1, I am using a prepare for segue to push data from VC1 to VC2 or VC3:</p>
  
  <pre><code>    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
      if segue.identifier == "segueToVC2” {
          let destinationViewController: VC2 = segue.destination as! VC2;
      destinationViewController.passedData1 = firstAmount
      destinationViewController.passedData2 = secondAmount
      destinationViewController.passedData3 = thirdAmount
  
      } else {
          let destinationViewController: VC3 = segue.destination as! VC3;
      destinationViewController.passedData1 = firstAmount
      destinationViewController.passedData2 = secondAmount
      destinationViewController.passedData3 = thirdAmount
      destinationViewController.passedData4 = fourthAmount
    }
  </code></pre>
  
  <p>By tapping the GO BACK button on each view, I return to the previous view:</p>
  
  <pre><code>@IBAction func goBackButtonPressed(_ sender: Any) {
      print("Back Button Pressed!")
      self.view.window?.rootViewController?.dismiss(animated: true, completion: nil)
  }
  </code></pre>
  
  <p>I am having trouble passing data backwards.  And when I return to VC2 from VC1, data has been reset to 0.  I have no segues going back from VC2 to VC1 or from VC3 to VC2.  Would that be the cleanest way to pass the data back: to create another segue in Main.storyboard from VC2 to VC1 and then add another ‘if’ to my prepare for segue that checks for VC1?</p>
  
  <p>I am passing ALL these variables back and forth between view controllers but only using some of them in each view controller.  It seems like a waste and I don't think I am on the right track here. </p>
  
  <p>Any help or suggestions?</p>