withContext for thread switching in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to switch to the IO dispatcher using withContext.

Android Kotlin

suspend fun fetchData() {
  withContext([1]) {
    // perform IO operation
  }
}

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ADispatchers.Main

BDispatchers.Default

CDispatchers.Unconfined

DDispatchers.IO

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.Main causes UI blocking.

Using Dispatchers.Default is for CPU-intensive tasks, not IO.

The Dispatchers.IO is used for IO-bound tasks like reading from disk or network calls.

2fill in blank

medium

Complete the code to switch back to the Main dispatcher after an IO operation.

Android Kotlin

suspend fun updateUI() {
  withContext(Dispatchers.IO) {
    // fetch data
  }
  withContext([1]) {
    // update UI
  }
}

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ADispatchers.IO

BDispatchers.Unconfined

CDispatchers.Main

DDispatchers.Default

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.IO for UI updates causes exceptions.

Using Dispatchers.Default does not guarantee main thread execution.

UI updates must happen on the Main dispatcher to avoid crashes.

3fill in blank

hard

Fix the error in the code by choosing the correct dispatcher for CPU-intensive work.

Android Kotlin

suspend fun calculate() {
  withContext([1]) {
    // heavy computation
  }
}

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ADispatchers.IO

BDispatchers.Default

CDispatchers.Main

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.IO for CPU work can cause thread starvation.

Using Dispatchers.Main blocks the UI.

Dispatchers.Default is optimized for CPU-intensive tasks like calculations.

4fill in blank

hard

Fill both blanks to correctly switch context for network call and UI update.

Android Kotlin

suspend fun loadData() {
  withContext([1]) {
    // network call
  }
  withContext([2]) {
    // update UI
  }
}

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ADispatchers.IO

BDispatchers.Main

CDispatchers.Default

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the dispatchers causes UI crashes or blocking.

Using Dispatchers.Default for network calls is inefficient.

Network calls run on Dispatchers.IO, UI updates on Dispatchers.Main.

5fill in blank

hard

Fill all three blanks to create a map of word lengths filtering words longer than 4 characters.

Android Kotlin

suspend fun processWords(words: List<String>): Map<String, Int> = withContext([1]) {
  words.associateWith { word -> word.length }
}.filter { (word, length) -> length [2] [3] }

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ADispatchers.Default

B>

C4

DDispatchers.IO

Attempts:

3 left

💡 Hint

Common Mistakes

Using IO dispatcher for length calculation is inefficient.

Using wrong comparison operator or number in filter.

Use Dispatchers.Default for CPU work, filter lengths greater than 4.