Task and TaskGroup in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple asynchronous task that prints a message.

iOS Swift

Task {
    print([1])
}

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

ATask.sleep(1_000_000_000)

BHello from Task!

Cprint("Hello from Task!")

D"Hello from Task!"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the string.

Trying to print without a string argument.

The print function requires a string argument in quotes. Option D correctly provides a string literal.

2fill in blank

medium

Complete the code to create a TaskGroup that runs two tasks concurrently.

iOS Swift

Task {
    await withTaskGroup(of: Void.self) { group in
        group.addTask {
            print("Task 1")
        }
        group.addTask {
            print([1])
        }
    }
}

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

Aprint("Task 2")

BTask 2

C"Task 2"

DTask.sleep(1_000_000_000)

Attempts:

3 left

💡 Hint

Common Mistakes

Missing quotes around the string.

Trying to call print inside print.

Inside the print function, the argument must be a string literal with quotes. Option C is correct.

3fill in blank

hard

Fix the error in the TaskGroup code by completing the blank with the correct keyword to wait for all tasks.

iOS Swift

Task {
    [1] withTaskGroup(of: Int.self) { group in
        group.addTask { 1 }
        group.addTask { 2 }
    }
}

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

Aawait

Basync

Ctry

Dyield

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' instead of 'await'.

Omitting the keyword entirely.

The 'await' keyword is needed to wait for the TaskGroup to complete its tasks asynchronously.

4fill in blank

hard

Fill both blanks to create a TaskGroup that returns the sum of two asynchronous tasks.

iOS Swift

let sum = await withTaskGroup(of: Int.self) { group in
    group.addTask { 5 }
    group.addTask { 10 }
    var total = 0
    for await [1] in group {
        total [2] [1]
    }
    return total
}

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

Avalue

B+=

C-=

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' instead of '+='.

Using a loop variable name not matching the code.

The loop variable should be 'value' to hold each task result, and '+=' adds it to total.

5fill in blank

hard

Fill all three blanks to create a TaskGroup that returns the maximum value from three asynchronous tasks.

iOS Swift

let maxValue = await withTaskGroup(of: Int.self) { group in
    group.addTask { 3 }
    group.addTask { 7 }
    group.addTask { 5 }
    var maxVal = Int.min
    for await [1] in group {
        if [1] [2] maxVal {
            maxVal = [1]
        }
    }
    return maxVal
}

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

Aresult

B>

C<

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the comparison.

Using inconsistent variable names.

The loop variable is 'result'. We compare if result > maxVal, then update maxVal with result.

Practice

1. What is the main purpose of a Task in Swift concurrency?

easy

A. To run a single background job asynchronously

B. To group multiple tasks and run them together

C. To update the UI on the main thread

D. To pause the app execution

Solution

1. Step 1: Understand what Task does

   A Task is designed to run one asynchronous job in the background.

2. Step 2: Differentiate from TaskGroup

   TaskGroup runs many jobs together, not a single job.

3. Final Answer:

   To run a single background job asynchronously -> Option A

4. Quick Check:

   Task = single background job [OK]

Hint: Task runs one job; TaskGroup runs many [OK]

Common Mistakes:

• Confusing Task with TaskGroup
• Thinking Task updates UI directly
• Assuming Task pauses app execution

2. Which of the following is the correct syntax to create a Task that prints "Hello" asynchronously?

easy

A. async Task { print("Hello") }

B. TaskGroup { print("Hello") }

C. Task.run { print("Hello") }

D. Task { print("Hello") }

Solution

1. Step 1: Recall correct Task syntax

   The correct way to create a Task is using Task { ... } with a closure.

2. Step 2: Check other options for errors

   TaskGroup is not used like this; async Task and Task.run are invalid syntax.

3. Final Answer:

   Task { print("Hello") } -> Option D

4. Quick Check:

   Correct Task syntax = Task { print("Hello") } [OK]

Hint: Use Task { } with closure for async code [OK]

Common Mistakes:

• Using TaskGroup instead of Task
• Adding 'async' keyword before Task
• Trying to call Task.run which doesn't exist

3. What will be printed by this Swift code using TaskGroup?

func fetchData() async {
  await withTaskGroup(of: String.self) { group in
    group.addTask { "A" }
    group.addTask { "B" }
    for await result in group {
      print(result)
    }
  }
}
fetchData()

medium

A. Either A then B or B then A (order not guaranteed)

B. B then A in order

C. A then B in order

D. No output because of syntax error

Solution

1. Step 1: Understand TaskGroup concurrency

   TaskGroup runs tasks concurrently and collects results as they finish, order is not guaranteed.

2. Step 2: Analyze the code output

   Since tasks return "A" and "B" concurrently, the print order can be either "A" then "B" or "B" then "A".

3. Final Answer:

   Either A then B or B then A (order not guaranteed) -> Option A

4. Quick Check:

   TaskGroup results order is unpredictable [OK]

Hint: TaskGroup runs tasks concurrently; output order varies [OK]

Common Mistakes:

• Assuming TaskGroup results are always ordered
• Thinking tasks run sequentially
• Believing syntax error prevents output

4. Identify the error in this Swift code using TaskGroup:

await withTaskGroup(of: Int.self) { group in
  group.addTask { 1 }
  group.addTask { 2 }
  for result in group {
    print(result)
  }
}

medium

A. Incorrect type in 'withTaskGroup' declaration

B. Using 'for' instead of 'for await' to iterate the group

C. Missing 'await' before 'for' loop

D. Cannot add tasks inside 'withTaskGroup'

Solution

1. Step 1: Check iteration over TaskGroup

   Iteration over a TaskGroup is asynchronous, so it requires for await.

2. Step 2: Identify the error in the code

   The code uses for result in group without await, causing a compile error.

3. Final Answer:

   Using 'for' instead of 'for await' to iterate the group -> Option B

4. Quick Check:

   Async iteration needs 'for await' [OK]

Hint: Use 'for await' to loop over TaskGroup results [OK]

Common Mistakes:

• Forgetting 'await' in asynchronous loops
• Confusing TaskGroup type declaration
• Thinking tasks can't be added inside withTaskGroup

5. You want to fetch user data from three different servers concurrently and combine the results. Which Swift concurrency pattern using TaskGroup is best to achieve this?

hard

A. Create three separate Task instances and wait for each sequentially

B. Run three synchronous functions one after another on the main thread

C. Use a TaskGroup to add three tasks fetching data, then collect all results asynchronously

D. Use a single Task that fetches data from all servers sequentially

Solution

1. Step 1: Understand concurrency needs

   Fetching from three servers concurrently requires running tasks in parallel to save time.

2. Step 2: Choose the best Swift concurrency pattern

   TaskGroup allows adding multiple tasks and collecting results asynchronously, perfect for this use case.

3. Final Answer:

   Use a TaskGroup to add three tasks fetching data, then collect all results asynchronously -> Option C

4. Quick Check:

   TaskGroup = concurrent multiple tasks [OK]

Hint: Use TaskGroup for multiple concurrent tasks and results [OK]

Common Mistakes:

• Running tasks sequentially losing concurrency benefits
• Using synchronous calls blocking main thread
• Using single Task for sequential fetches