SharedFlow for events in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a MutableSharedFlow for events.

Android Kotlin

val eventFlow = MutableSharedFlow<[1]>()

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

AString

BBoolean

CInt

DFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using a numeric type when events are text messages.

Forgetting to specify the type parameter.

The MutableSharedFlow is declared with the type of events it will emit. Here, String is used for simple text events.

2fill in blank

medium

Complete the code to emit an event string into the SharedFlow.

Android Kotlin

viewModelScope.launch {
  eventFlow.[1]("ButtonClicked")
}

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

Acollect

Bsubscribe

Cemit

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using collect which is for receiving, not sending.

Using send which is for Channels, not SharedFlow.

To send an event to the SharedFlow, use the emit function inside a coroutine.

3fill in blank

hard

Fix the error in collecting events from the SharedFlow in a lifecycle-aware way.

Android Kotlin

lifecycleScope.launchWhenStarted {
  eventFlow.[1] { event ->
    handleEvent(event)
  }
}

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

Asubscribe

Bemit

Claunch

Dcollect

Attempts:

3 left

💡 Hint

Common Mistakes

Using emit which is for sending events.

Using subscribe which is not a Kotlin Flow function.

To receive events from a SharedFlow, use the collect function inside a coroutine.

4fill in blank

hard

Fill both blanks to create a SharedFlow that replays the last event and has no extra buffer.

Android Kotlin

val eventFlow = MutableSharedFlow<String>(replay = [1], extraBufferCapacity = [2])

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

A1

B0

C2

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Setting replay to zero loses the last event for new subscribers.

Setting extraBufferCapacity too high can cause unexpected buffering.

Setting replay = 1 makes the flow replay the last event to new subscribers. extraBufferCapacity = 0 means no extra buffering.

5fill in blank

hard

Fill all three blanks to collect events from SharedFlow in a Compose UI using LaunchedEffect.

Android Kotlin

LaunchedEffect(Unit) {
  eventFlow.[1] { event ->
    when(event) {
      [2] -> showToast("Clicked")
      [3] -> showToast("Error")
    }
  }
}

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

Acollect

B"ButtonClicked"

C"ErrorOccurred"

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using emit instead of collect to receive events.

Using incorrect event string literals in the when statement.

Use collect to receive events. Match event strings to show appropriate messages.

Practice

1. What is the primary purpose of using SharedFlow in Android Kotlin apps?

easy

A. To manage background threads automatically

B. To store large amounts of data persistently

C. To send events to multiple listeners safely and efficiently

D. To replace all UI components with reactive streams

Solution

1. Step 1: Understand SharedFlow's role

   SharedFlow is designed to broadcast events to multiple collectors without losing any events.

2. Step 2: Compare with other options

   It is not for data storage, UI replacement, or thread management.

3. Final Answer:

   To send events to multiple listeners safely and efficiently -> Option C

4. Quick Check:

   SharedFlow = event broadcasting [OK]

Hint: SharedFlow broadcasts events to many listeners [OK]

Common Mistakes:

• Confusing SharedFlow with data storage solutions
• Thinking SharedFlow manages threads automatically
• Assuming SharedFlow replaces UI components

2. Which of the following is the correct way to emit an event using a MutableSharedFlow named eventFlow?

easy

A. eventFlow.emit("New Event")

B. eventFlow.collect { "New Event" }

C. eventFlow.send("New Event")

D. eventFlow.postValue("New Event")

Solution

1. Step 1: Identify the correct emission method

   MutableSharedFlow uses emit() to send events.

2. Step 2: Eliminate incorrect methods

   collect() is for receiving, send() is for Channels, and postValue() is for LiveData.

3. Final Answer:

   eventFlow.emit("New Event") -> Option A

4. Quick Check:

   Emit events with emit() [OK]

Hint: Use emit() to send events on SharedFlow [OK]

Common Mistakes:

• Using collect() to send events
• Confusing SharedFlow with Channel's send()
• Using LiveData's postValue() with SharedFlow

3. Given the following code snippet, what will be printed when the event is emitted?

val eventFlow = MutableSharedFlow<String>()

fun observe() {
  eventFlow.collect { println(it) }
}

fun sendEvent() {
  eventFlow.emit("Hello")
}

sendEvent()
observe()

medium

A. Compilation error

B. Hello printed twice

C. No output

D. Hello

Solution

1. Step 1: Analyze suspend function calls

   Both emit() and collect() are suspend functions called from non-suspend functions and top-level code without a coroutine scope.

2. Step 2: Result of invalid calls

   Suspend functions cannot be called from non-suspend contexts, causing a compilation error.

3. Final Answer:

   Compilation error -> Option A

4. Quick Check:

   suspend emit/collect outside coroutine = compile error [OK]

Hint: emit() and collect() must be called in coroutines [OK]

Common Mistakes:

• Overlooking that emit() and collect() are suspend functions
• Assuming the code compiles and runs to test replay behavior
• Forgetting coroutine requirements for Flow operations

4. Identify the problem in this code snippet using SharedFlow:

val eventFlow = MutableSharedFlow<String>()

fun start() {
  eventFlow.emit("Start")
}

fun listen() {
  eventFlow.collect { println(it) }
}

start()
listen()

medium

A. No problem, code works fine

B. collect() is called without a coroutine

C. MutableSharedFlow cannot emit strings

D. emit() is called outside a coroutine

Solution

1. Step 1: Check emit() usage

   emit() is a suspend function and must be called inside a coroutine.

2. Step 2: Check collect() usage

   collect() is also suspend and needs a coroutine, but the question focuses on emit() first.

3. Final Answer:

   emit() is called outside a coroutine -> Option D

4. Quick Check:

   emit() requires coroutine context [OK]

Hint: emit() must run inside a coroutine [OK]

Common Mistakes:

• Calling emit() directly without coroutine
• Ignoring suspend nature of collect()
• Thinking MutableSharedFlow restricts data types

5. You want to show a toast message every time a button is clicked using SharedFlow. Which approach correctly ensures the toast shows for each click even if the UI is recreated?

hard

A. Use a MutableSharedFlow with no replay and emit on button click

B. Use a MutableSharedFlow with replay = 1 and emit on button click

C. Use a StateFlow to hold the last toast message and emit on button click

D. Use LiveData to send the toast message on button click

Solution

1. Step 1: Understand event replay needs

   To show toast after UI recreation, events must replay at least once.

2. Step 2: Choose correct flow type and replay

   MutableSharedFlow with replay=1 replays last event to new collectors, ensuring toast shows.

3. Step 3: Compare other options

   No replay means missed events; StateFlow holds state, not events; LiveData is not SharedFlow.

4. Final Answer:

   Use a MutableSharedFlow with replay = 1 and emit on button click -> Option B

5. Quick Check:

   Replay 1 ensures event delivery after UI recreation [OK]

Hint: Set replay=1 to resend last event to new collectors [OK]

Common Mistakes:

• Using no replay and missing events after UI changes
• Confusing StateFlow state with event replay
• Using LiveData instead of SharedFlow for events