Why network calls fetch remote data in Android Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a network call using Kotlin coroutines.

Android Kotlin

GlobalScope.launch {
    val response = [1]("https://example.com/data.json")
}

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

AfetchData

BfetchFromNetwork

CfetchRemoteData

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that does not exist or is not standard.

Trying to call a network function without coroutine scope.

The fetch function is used here to represent a network call that fetches remote data asynchronously.

2fill in blank

medium

Complete the code to convert the network response to a string.

Android Kotlin

val data = response.[1]()

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

AreadText

BtoString

CtoJson

DtoByteArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using toString() which does not read the content but returns object info.

Using toJson() which is not a standard function.

The readText() function reads the response body as a string, which is common after fetching remote data.

3fill in blank

hard

Fix the error in the code to make the network call on the main thread safe.

Android Kotlin

runBlocking {
    val result = withContext([1]) {
        fetch("https://example.com")
    }
}

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

ADispatchers.Main

BDispatchers.IO

CDispatchers.Default

DDispatchers.Unconfined

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.Main which blocks the UI.

Using Dispatchers.Default which is for CPU-intensive tasks.

Network calls should run on Dispatchers.IO to avoid blocking the main thread and keep the app responsive.

4fill in blank

hard

Fill both blanks to create a simple function that fetches remote data and returns it as a string.

Android Kotlin

suspend fun getData(url: String): String {
    return withContext([1]) {
        val response = fetch(url)
        response.[2]()
    }
}

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

ADispatchers.IO

BDispatchers.Main

CreadText

DtoString

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dispatchers.Main which blocks UI.

Using toString() which does not read response content.

The function uses Dispatchers.IO to run the network call safely and readText() to get the response as a string.

5fill in blank

hard

Fill all three blanks to create a coroutine that fetches data and updates the UI safely.

Android Kotlin

GlobalScope.launch {
    val data = withContext([1]) {
        fetch("https://api.example.com")
            .[2]()
    }
    withContext([3]) {
        textView.text = data
    }
}

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

ADispatchers.IO

BreadText

CDispatchers.Main

DtoString

Attempts:

3 left

💡 Hint

Common Mistakes

Updating UI on IO dispatcher causing crashes.

Not reading response content properly.

The network call runs on Dispatchers.IO, the response is read as text with readText(), and the UI update runs on Dispatchers.Main to keep the app responsive.

Practice

1. Why do mobile apps use network calls to fetch data from the internet?

easy

A. To get the most up-to-date information that changes frequently

B. To save battery by avoiding local storage

C. To make the app run faster without internet

D. To store data permanently on the device

Solution

1. Step 1: Understand the purpose of network calls

   Network calls are used to get fresh data from the internet, especially when data changes often.

2. Step 2: Compare options with this purpose

   Only To get the most up-to-date information that changes frequently matches this reason; others are incorrect because network calls do not save battery or store data locally.

3. Final Answer:

   To get the most up-to-date information that changes frequently -> Option A

4. Quick Check:

   Network calls fetch fresh data = A [OK]

Hint: Network calls get fresh data from internet, not local storage [OK]

Common Mistakes:

• Thinking network calls save battery
• Assuming network calls store data locally
• Believing network calls make app work offline

2. Which Kotlin code snippet correctly starts a network call on a background thread?

easy

A. fetchDataFromNetwork()

B. Thread.sleep(1000); fetchDataFromNetwork()

C. runOnUiThread { fetchDataFromNetwork() }

D. GlobalScope.launch { fetchDataFromNetwork() }

Solution

1. Step 1: Identify correct background thread usage in Kotlin

   Using GlobalScope.launch starts a coroutine on a background thread for network calls.

2. Step 2: Check other options for thread usage

   fetchDataFromNetwork() runs on main thread, runOnUiThread { fetchDataFromNetwork() } forces main thread, Thread.sleep(1000); fetchDataFromNetwork() just delays but runs on main thread.

3. Final Answer:

   GlobalScope.launch { fetchDataFromNetwork() } -> Option D

4. Quick Check:

   Background thread with coroutine = B [OK]

Hint: Use coroutines (launch) for background network calls in Kotlin [OK]

Common Mistakes:

• Calling network on main thread causing app freeze
• Using runOnUiThread for network calls
• Using Thread.sleep to delay network calls

3. What will this Kotlin code print if the network call returns "Hello" asynchronously?

GlobalScope.launch {
  val result = fetchDataFromNetwork()
  println(result)
}
println("Done")

medium

A. Hello\nDone

B. Done\nHello

C. HelloHello

D. DoneDone

Solution

1. Step 1: Understand coroutine asynchronous behavior

   The println("Done") runs immediately on main thread before coroutine finishes.

2. Step 2: Determine print order

   Coroutine prints "Hello" after network call completes, so output is "Done" then "Hello".

3. Final Answer:

   Done\nHello -> Option B

4. Quick Check:

   Async coroutine prints after main thread = A [OK]

Hint: Main thread prints first, coroutine prints after network call [OK]

Common Mistakes:

• Assuming coroutine blocks main thread
• Expecting prints in code order
• Ignoring asynchronous nature of network calls

4. Identify the error in this Kotlin code that fetches data from network:

fun fetch() {
  val data = fetchDataFromNetwork()
  println(data)
}

fun fetchDataFromNetwork(): String {
  Thread.sleep(2000)
  return "Data"
}

medium

A. Thread.sleep is not allowed in Kotlin

B. fetchDataFromNetwork() returns wrong data type

C. Network call is blocking main thread causing app freeze

D. println cannot print strings

Solution

1. Step 1: Analyze fetchDataFromNetwork() behavior

   Thread.sleep(2000) blocks the thread it runs on, here main thread, freezing UI.

2. Step 2: Understand impact on app

   Blocking main thread causes app to freeze, so network calls must run on background thread.

3. Final Answer:

   Network call is blocking main thread causing app freeze -> Option C

4. Quick Check:

   Blocking main thread with sleep = C [OK]

Hint: Never block main thread with network calls or sleep [OK]

Common Mistakes:

• Ignoring UI freeze caused by blocking calls
• Thinking Thread.sleep is forbidden syntax
• Assuming println cannot print strings

5. You want to fetch a large list of user data from a server that updates every minute. Which approach is best to keep your Android app smooth and up-to-date?

hard

A. Use background network calls with caching and refresh every minute

B. Fetch data on main thread every time user opens screen

C. Avoid network calls and use static data bundled in app

D. Fetch data once at app start and store locally forever

Solution

1. Step 1: Consider data freshness and app performance

   Data updates every minute, so app needs fresh data regularly without freezing UI.

2. Step 2: Evaluate options for smoothness and freshness

   Use background network calls with caching and refresh every minute uses background calls with caching and periodic refresh, balancing smooth UI and fresh data.

3. Final Answer:

   Use background network calls with caching and refresh every minute -> Option A

4. Quick Check:

   Background fetch + caching = D [OK]

Hint: Combine background fetch with caching for smooth, fresh data [OK]

Common Mistakes:

• Fetching on main thread causing freezes
• Not refreshing data causing stale info
• Using static data ignoring updates