Coroutines for async networking in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you launch a coroutine on the Main dispatcher?

Consider this Kotlin coroutine code snippet in an Android app:

GlobalScope.launch(Dispatchers.Main) {
  val data = fetchDataFromNetwork()
  updateUI(data)
}

What is the expected behavior of this code?

Android Kotlin

GlobalScope.launch(Dispatchers.Main) {
  val data = fetchDataFromNetwork()
  updateUI(data)
}

A The network call runs asynchronously on a background thread, then updates the UI on the main thread.

B The network call runs on the main thread, freezing the UI until it finishes.

C The coroutine throws an exception because network calls are not allowed on the main thread.

D The updateUI function runs on a background thread, causing UI errors.

💡 Hint

Remember that Dispatchers.Main runs coroutine code on the UI thread but suspend functions can switch threads internally.

Using Dispatchers.Main launches the coroutine on the UI thread. However, suspend functions like fetchDataFromNetwork() typically switch to a background thread internally, so the UI stays responsive. After the network call completes, updateUI runs on the main thread safely.

❓ lifecycle

intermediate

What is the risk of using GlobalScope for network calls in Android?

In Android, what problem can occur if you launch network coroutines using GlobalScope.launch without tying them to a lifecycle?

A The coroutine may continue running after the activity is destroyed, causing memory leaks or crashes.

B The coroutine will automatically cancel when the activity is destroyed.

C GlobalScope does not support network calls, so the coroutine will fail immediately.

D The coroutine will run on the main thread and block the UI.

💡 Hint

Think about what happens when the user leaves the screen while a coroutine is still running.

GlobalScope coroutines live as long as the app process. If the activity is destroyed, the coroutine keeps running and may try to update a non-existent UI, causing crashes or memory leaks.

📝 Syntax

advanced

Which code snippet correctly performs a network call asynchronously using coroutines?

Choose the Kotlin code that correctly fetches data from a network on a background thread and updates the UI on the main thread.

A

launch {
  val data = withContext(Dispatchers.Main) { fetchData() }
  updateUI(data)
}

B

launch(Dispatchers.Main) {
  val data = fetchData()
  updateUI(data)
}

C

launch(Dispatchers.IO) {
  val data = fetchData()
  withContext(Dispatchers.Main) {
    updateUI(data)
  }
}

D

launch(Dispatchers.IO) {
  val data = fetchData()
  updateUI(data)
}

💡 Hint

Network calls should run on IO dispatcher, UI updates on Main dispatcher.

Option C runs fetchData() on the IO dispatcher (background thread), then switches to Main dispatcher to update UI safely. Option C runs fetchData() on Main thread, blocking UI. Option C runs fetchData() on Main thread inside withContext, blocking UI. Option C updates UI from IO thread, causing errors.

🔧 Debug

advanced

Why does this coroutine code cause a crash when updating UI?

Given this code:

GlobalScope.launch(Dispatchers.IO) {
  val data = fetchData()
  updateUI(data)
}

Why does the app crash when updateUI is called?

Android Kotlin

GlobalScope.launch(Dispatchers.IO) {
  val data = fetchData()
  updateUI(data)
}

A fetchData() is not a suspend function, causing a runtime error.

B updateUI is called from a background thread, which is not allowed for UI updates.

C GlobalScope does not support Dispatchers.IO, causing a crash.

D The coroutine is not launched, so updateUI is never called.

💡 Hint

UI updates must happen on the main thread.

Dispatchers.IO runs on a background thread. Calling updateUI from there causes Android to crash because UI changes must happen on the main thread.

🧠 Conceptual

expert

What is the main advantage of using suspend functions with coroutines for networking?

Why do suspend functions combined with coroutines improve networking code in Android apps?

A They run all network calls on the main thread for faster UI updates.

B They automatically retry failed network calls without extra code.

C They block the main thread until the network call finishes, ensuring data consistency.

D They allow writing asynchronous code in a sequential style without blocking threads.

💡 Hint

Think about how suspend functions let you write code that looks simple but runs asynchronously.

Suspend functions let you write code that looks like normal sequential code but actually suspends without blocking threads. This makes asynchronous networking code easier to read and maintain.