StateFlow for reactive state in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a MutableStateFlow with initial value 0.

Android Kotlin

val counter = MutableStateFlow([1])

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

Afalse

B"0"

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "0" instead of integer 0

Leaving the initial value null

Using a boolean false instead of a number

The MutableStateFlow must be initialized with a starting value. Here, 0 is the correct integer initial value.

2fill in blank

medium

Complete the code to expose the StateFlow as a read-only flow from MutableStateFlow.

Android Kotlin

val _counter = MutableStateFlow(0)
val counter: StateFlow<Int> = _counter.[1]

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AtoFlow()

BtoStateFlow()

CasStateFlow()

Dstate()

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent function like toStateFlow()

Trying to assign MutableStateFlow directly without conversion

Using toFlow() which returns a Flow, not StateFlow

Use asStateFlow() to expose a read-only StateFlow from a MutableStateFlow.

3fill in blank

hard

Fix the error in updating the MutableStateFlow value inside a function.

Android Kotlin

fun increment() {
  _counter.[1] = _counter.value + 1
}

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Avalue

BsetValue

Cemit

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using emit which is a suspend function and not available on MutableStateFlow

Trying to call setValue which does not exist

Using update which is an extension function but not a property

To update the value of a MutableStateFlow, assign the new value to its value property.

4fill in blank

hard

Fill both blanks to collect the StateFlow in a lifecycle-aware way inside a Fragment.

Android Kotlin

viewLifecycleOwner.lifecycleScope.launchWhenStarted {
  counter.[1] { value ->
    textView.text = value.toString()
  }
}

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Acollect

BcollectLatest

Claunch

Dobserve

Attempts:

3 left

💡 Hint

Common Mistakes

Using collectLatest which cancels previous collector but not necessary here

Using launch which is for starting coroutines, not collecting flows

Using observe which is for LiveData, not StateFlow

Use collect to observe StateFlow emissions inside a coroutine.

5fill in blank

hard

Fill both blanks to create a StateFlow that holds a list of strings and add a new item.

Android Kotlin

private val _items = MutableStateFlow<List<String>>([1])
val items: StateFlow<List<String>> = _items.asStateFlow()

fun addItem(newItem: String) {
  _items.value = _items.value [2] listOf(newItem)
}

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

AemptyList()

B+

Cplus

DlistOf()

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing with listOf() without elements

Using + operator which works but plus() is clearer for lists

Trying to modify the list directly instead of creating a new list

Initialize with an empty list using emptyList(). Use plus to add an item to the list immutably.