Passing data to destination in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable to hold data to pass.

iOS Swift

var message[1] String?

Drag options to blanks, or click blank then click option'

A?

B:

C=

D!

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of ':' when declaring a variable type.

Using '!' or '?' incorrectly here.

In Swift, to declare a variable with a type, use a colon : after the variable name.

2fill in blank

medium

Complete the code to override the prepare method for passing data.

iOS Swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showDetail" {
        let destination = segue.[1] as! DetailViewController
    }
}

Drag options to blanks, or click blank then click option'

Adestination

BdestinationVC

CdestinationViewController

DdestinationView

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong property name like 'destinationVC' or 'destinationView'.

Forgetting to cast to the correct controller type.

The correct property to get the destination view controller from a segue is destination.

3fill in blank

hard

Fix the error in passing data to the destination view controller.

iOS Swift

destination.message = [1]

Drag options to blanks, or click blank then click option'

Aself.message

Bself.message()

C"message"

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes which assign a string literal instead of the variable value.

Calling the variable like a function with parentheses.

You assign the variable message directly without self. or parentheses.

4fill in blank

hard

Fill both blanks to safely unwrap and pass data in prepare method.

iOS Swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let destination = segue.[1] as? DetailViewController, let data = [2] {
        destination.message = data
    }
}

Drag options to blanks, or click blank then click option'

AdestinationViewController

Bself.message

Cmessage

Dsender

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sender' instead of the data variable.

Using forced cast instead of optional cast.

Use destination to get the destination safely and unwrap the message variable.

5fill in blank

hard

Fill all three blanks to create a dictionary and pass filtered data to destination.

iOS Swift

let filteredData = data.filter { $0.[1] [2] [3] }
destination.filteredItems = filteredData

Drag options to blanks, or click blank then click option'

Acount

B>

C5

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' which is not a Swift property.

Using '<' instead of '>' causing wrong filtering.

Use count to get the length of each item, filter those with count greater than 5.

Practice

1. What is the main purpose of passing data to a destination view controller in iOS Swift?

easy

A. To change the app's theme colors dynamically

B. To handle user authentication automatically

C. To improve app performance by caching data

D. To share information so the next screen can display relevant content

Solution

1. Step 1: Understand data sharing between screens

   Passing data allows one screen to send information to another so the next screen can show content based on that data.

2. Step 2: Identify the purpose of passing data

   This process is mainly to make the user experience relevant by showing specific information on the destination screen.

3. Final Answer:

   To share information so the next screen can display relevant content -> Option D

4. Quick Check:

   Passing data = share info for relevant display [OK]

Hint: Passing data means sharing info for next screen display [OK]

Common Mistakes:

• Confusing data passing with UI styling
• Thinking it improves performance directly
• Assuming it handles authentication

2. Which method is commonly overridden to pass data to the destination view controller before a segue?

easy

A. prepare(for:sender:)

B. applicationDidBecomeActive()

C. viewWillAppear()

D. viewDidLoad()

Solution

1. Step 1: Identify the method for segue preparation

   The method prepare(for:sender:) is called before a segue happens and is used to set data on the destination controller.

2. Step 2: Confirm other methods are unrelated

   viewDidLoad() and viewWillAppear() are lifecycle methods but not used for passing data during segue. applicationDidBecomeActive() is an app lifecycle method.

3. Final Answer:

   prepare(for:sender:) -> Option A

4. Quick Check:

   Data passing before segue = prepare(for:sender:) [OK]

Hint: Use prepare(for:sender:) to pass data before segue [OK]

Common Mistakes:

• Using viewDidLoad() to pass data
• Confusing lifecycle methods with segue methods
• Trying to pass data after segue completes

3. Given the code snippet below, what will be the value of destinationVC.userName after the segue?

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

medium

A. "Alice"

B. nil

C. An empty string ""

D. Causes a runtime crash

Solution

1. Step 1: Check the segue identifier and casting

   The code checks if the segue identifier is "showDetail" and casts the destination to DetailViewController safely using forced cast.

2. Step 2: Assign the userName property

   It sets destinationVC.userName to "Alice" before the segue completes.

3. Final Answer:

   "Alice" -> Option A

4. Quick Check:

   prepare sets userName = "Alice" [OK]

Hint: Check identifier and cast before assigning data [OK]

Common Mistakes:

• Forgetting to check segue.identifier
• Not casting destinationVC correctly
• Assuming userName remains nil

4. What is the error in the following code that causes a crash when performing the segue?

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

medium

A. Assigning data after the segue completes

B. Using forced cast instead of optional cast

C. Missing check for segue.identifier before casting

D. Not calling super.prepare(for:sender:)

Solution

1. Step 1: Identify missing segue identifier check

   The code casts destinationVC without checking if the segue.identifier matches the expected one, risking wrong destination type.

2. Step 2: Understand crash cause

   If the segue is not to DetailViewController, forced cast fails and crashes the app.

3. Final Answer:

   Missing check for segue.identifier before casting -> Option C

4. Quick Check:

   Always check segue.identifier before casting [OK]

Hint: Always check segue.identifier before casting destination [OK]

Common Mistakes:

• Skipping identifier check causes crash
• Assuming forced cast is always safe
• Ignoring optional cast or guard statements

5. You want to pass a user's score (an Int) from GameViewController to ResultViewController using a segue with identifier "showResult". Which code snippet correctly passes the score safely?

hard

A. override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showResult" {
let dest = segue.destination as! ResultViewController
dest.score = userScore
}
}

B. override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showResult" {
guard let dest = segue.destination as? ResultViewController else { return }
dest.score = userScore
}
}

C. override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let dest = segue.destination as? ResultViewController
dest?.score = userScore
}

D. override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showResult" {
let dest = segue.destination
dest.score = userScore
}
}

Solution

1. Step 1: Check segue identifier and safely cast destination

   override func prepare(for segue: UIStoryboardSegue, sender: Any?) { if segue.identifier == "showResult" { guard let dest = segue.destination as? ResultViewController else { return } dest.score = userScore } } uses a guard let to safely cast segue.destination to ResultViewController only if the identifier matches "showResult".

2. Step 2: Assign the score property safely

   Inside the guard, dest.score is assigned userScore safely, avoiding crashes if cast fails.

3. Final Answer:

   Checks identifier and uses guard let for safe casting -> Option B

4. Quick Check:

   Safe cast + identifier check = override func prepare(for segue: UIStoryboardSegue, sender: Any?) { if segue.identifier == "showResult" { guard let dest = segue.destination as? ResultViewController else { return } dest.score = userScore } } [OK]

Hint: Use guard let with identifier check for safe data passing [OK]

Common Mistakes:

• Forcing cast without identifier check (Option A)
• Not checking identifier before casting (Option B)
• Not casting destination at all (Option D)