Passing data to destination in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Passing data using prepare(for:sender:)

What will be the value of destinationVC.receivedText after this segue is performed?

iOS Swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  if segue.identifier == "showDetail" {
    let destinationVC = segue.destination as! DetailViewController
    destinationVC.receivedText = "Hello Swift"
  }
}

A "Hello Swift"

B nil

C "showDetail"

D Crash due to wrong cast

💡 Hint

Remember that prepare(for:sender:) is called before the segue happens and you can set properties on the destination view controller.

The code safely casts the destination view controller and sets its receivedText property to "Hello Swift" before the segue happens, so the destinationVC.receivedText will be "Hello Swift".

❓ navigation

intermediate

Passing data with programmatic navigation

What will be printed when the button is tapped?

iOS Swift

class FirstViewController: UIViewController {
  @IBAction func buttonTapped(_ sender: UIButton) {
    let secondVC = SecondViewController()
    secondVC.data = "Swift Rocks"
    navigationController?.pushViewController(secondVC, animated: true)
  }
}

class SecondViewController: UIViewController {
  var data: String?
  override func viewDidLoad() {
    super.viewDidLoad()
    print(data ?? "No data")
  }
}

A No data

B nil

C Swift Rocks

D Crash due to missing storyboard

💡 Hint

Check when viewDidLoad is called and if the data property is set before that.

The data property is set before pushing the view controller, so when viewDidLoad runs, data contains "Swift Rocks" and it prints that.

❓ lifecycle

advanced

Data availability timing in destination VC

Why might receivedText be nil inside viewDidLoad() of the destination view controller when using a segue?

iOS Swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  let destinationVC = segue.destination as! DetailViewController
  DispatchQueue.main.async {
    destinationVC.receivedText = "Delayed Data"
  }
}

class DetailViewController: UIViewController {
  var receivedText: String?
  override func viewDidLoad() {
    super.viewDidLoad()
    print(receivedText ?? "No data")
  }
}

A Because prepare(for:sender:) is called after viewDidLoad

B Because the data is set asynchronously after viewDidLoad runs

C Because receivedText is private and inaccessible

D Because the segue identifier is missing

💡 Hint

Think about when the DispatchQueue.main.async block executes relative to viewDidLoad.

The data is assigned asynchronously on the main queue, which happens after viewDidLoad runs, so receivedText is still nil during viewDidLoad.

📝 Syntax

advanced

Correct syntax for passing data with segue

Which option correctly passes a string to the destination view controller's property message in prepare(for:sender:)?

iOS Swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  if segue.identifier == "showMessage" {
    let dest = segue.destination as! MessageViewController
    // Pass data here
  }
}

A dest.message := "Hello from source"

B dest.message == "Hello from source"

C dest.message <- "Hello from source"

D dest.message = "Hello from source"

💡 Hint

Remember the assignment operator in Swift.

Option D uses the correct assignment operator '=' to set the property. The others use invalid operators causing syntax errors.

🔧 Debug

expert

Why does data not appear in destination VC?

Given this code, why does the destination view controller's label show empty text after navigation?

iOS Swift

class FirstVC: UIViewController {
  var textToSend = "Important Data"
  override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let dest = segue.destination as! SecondVC
    dest.receivedText = textToSend
  }
}

class SecondVC: UIViewController {
  var receivedText: String?
  @IBOutlet weak var label: UILabel!
  override func viewDidLoad() {
    super.viewDidLoad()
    label.text = receivedText
  }
}

A The label outlet is not connected in storyboard, so label is nil

B receivedText is nil because prepare(for:) is not called

C viewDidLoad runs before prepare(for:), so label.text is empty

D The segue identifier is incorrect, so prepare(for:) is skipped

💡 Hint

Check if the label outlet is properly connected in Interface Builder.

If the label outlet is not connected, label is nil and setting label.text does nothing, so the label appears empty.