MainActor for UI updates in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to ensure the UI update runs on the main thread using MainActor.

iOS Swift

func updateLabel() {
  Task {
    await [1] {
      label.text = "Hello, world!"
    }
  }
}

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

AMainActor.run

BDispatchQueue.global().async

CTask.sleep

DDispatchQueue.main.asyncAfter

Attempts:

3 left

💡 Hint

Common Mistakes

Using background queues like DispatchQueue.global() causes UI update errors.

Forgetting to use await with MainActor.run.

Using MainActor.run ensures the code inside runs on the main thread, which is required for UI updates.

2fill in blank

medium

Complete the function declaration to mark it as running on the main actor.

iOS Swift

@[1]
func refreshUI() {
  label.text = "Updated"
}

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

AGlobalActor

BUIActor

CMainActor

DBackgroundActor

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect actor names like @GlobalActor or @BackgroundActor.

Omitting the @ symbol.

Marking the function with @MainActor ensures it always runs on the main thread for UI safety.

3fill in blank

hard

Fix the error in this async function to update UI safely on the main thread.

iOS Swift

func loadData() async {
  let data = await fetchData()
  await [1] {
    label.text = data
  }
}

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

ADispatchQueue.global().async

BDispatchQueue.main.sync

CTask.detached

DMainActor.run

Attempts:

3 left

💡 Hint

Common Mistakes

Using background queues for UI updates.

Using synchronous dispatch on main queue inside async code.

Using MainActor.run inside async functions ensures UI updates happen on the main thread safely.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters keys with length greater than 3 and converts keys to uppercase.

iOS Swift

let filteredDict = Dictionary(uniqueKeysWithValues: data.compactMap { key, value in
  guard key.count [1] 3 else { return nil }
  return (key.[2](), value)
})

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

A>

Blowercased

Cuppercased

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in the guard condition.

Using lowercased() instead of uppercased() for keys.

The guard checks keys longer than 3 characters using >. The keys are converted to uppercase with uppercased().

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that filters values greater than 10, converts keys to uppercase, and uses the value as is.

iOS Swift

let result = Dictionary(uniqueKeysWithValues: items.compactMap { key, value in
  guard value [1] 10 else { return nil }
  return (key.[2](), [3])
})

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

A<

B>

Cvalue

Duppercased

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > in the guard.

Swapping key and value in the return tuple.

The guard filters values greater than 10 using >. Keys are converted to uppercase with uppercased(). The value is returned as is.