Pass parameters / strings between view controllers programmatically (without using storyboard segues)

1. Create a new file called MyClass.swift as:

class MyClass {

    var string1 : String = ""

    var string2 : String = ""

    static let myInstance = MyClass()

}

2. Modify ViewController.swift as:

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {

        super.viewDidLoad()

        

        view.backgroundColor = UIColor.cyanColor()

        

        let myLabel = UILabel(frame: CGRectMake(50, 100, 300, 20))

        myLabel.text = "ViewController"

        view.addSubview(myLabel)

        

        let myButton = UIButton(frame: CGRectMake(50, 200, 100, 20))

        myButton.addTarget(self, action: "btnPressed:", forControlEvents: UIControlEvents.TouchUpInside)

        myButton.setTitle("Button", forState: UIControlState.Normal)

        myButton.setTitleColor(UIColor.blueColor(), forState: UIControlState.Normal)

        view.addSubview(myButton)

    }

    

    override func viewWillAppear(animated: Bool) {

        super.viewWillAppear(animated)

        

        let myLabelFrom = UILabel(frame: CGRectMake(50, 150, 300, 20))

        myLabelFrom.text = "From 2nd VC:\(MyClass.myInstance.string2)"

        myLabelFrom.tag = 50

        view.addSubview(myLabelFrom)

    }

    

    func btnPressed(sender: UIButton){

        //Remove myLabelFrom label because it will be drawn again in viewWillAppear()

        view.viewWithTag(50)?.removeFromSuperview()

        

        //Set the string to be passed to the second view controller.

        MyClass.myInstance.string1 = "String from VC"

        

        let secondVC = SecondViewController()

        

        //Set view controller transition animation style

        secondVC.modalTransitionStyle = UIModalTransitionStyle.CoverVertical

        self.presentViewController(secondVC, animated: true, completion: nil)

    }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

    }

}

3. Create a new file called SecondViewController.swift as:

import UIKit

class SecondViewController: UIViewController {

    override func viewDidLoad() {

        super.viewDidLoad()

        view.backgroundColor = UIColor.yellowColor()

        

        let myLabelSecond = UILabel(frame: CGRectMake(70, 150, 300, 20))

        myLabelSecond.text = "SecondViewController:"

        view.addSubview(myLabelSecond)

        let myLabelSecondFrom = UILabel(frame: CGRectMake(70, 200, 300, 20))

        myLabelSecondFrom.text = "From VC:\(MyClass.myInstance.string1)"

        view.addSubview(myLabelSecondFrom)

        

        let myButtonSecond = UIButton(frame: CGRectMake(70, 250, 100, 20))

        myButtonSecond.addTarget(self, action: "btnPressedSecond:", forControlEvents: UIControlEvents.TouchUpInside)

        myButtonSecond.setTitle("Back", forState: UIControlState.Normal)

        myButtonSecond.setTitleColor(UIColor.blueColor(), forState: UIControlState.Normal)

        view.addSubview(myButtonSecond)

    }

    func btnPressedSecond(sender: UIButton){

        //Set the string to be passed to the original view controller.

        MyClass.myInstance.string2 = "String from 2nd VC"

        dismissViewControllerAnimated(true, completion: nil)

    }

    

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

    }

}

Run the iOS simulator and the first view controller is shown as:

Press 'Button' and the second view controller with yellow background is shown as:

 After pressing the 'Back' button, the screen returns to the first view controller. The string from the second VC is now displayed.