Side effects (LaunchedEffect, SideEffect) in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a side effect in Jetpack Compose?

A side effect is an operation that affects something outside the scope of a composable function, like launching a coroutine, updating a variable, or interacting with the system.

beginner

What does LaunchedEffect do in Jetpack Compose?

LaunchedEffect runs a suspend function when the key(s) change or when the composable enters the composition. It is used to launch coroutines tied to the composable lifecycle.

intermediate

How does SideEffect differ from LaunchedEffect?

SideEffect runs synchronously after every successful recomposition to perform non-suspending side effects, while LaunchedEffect launches coroutines asynchronously.

beginner

When should you use LaunchedEffect in your composable?

Use LaunchedEffect when you want to run suspend functions or launch coroutines that depend on some state or key and should be cancelled and restarted when that key changes.

intermediate

Give an example of a side effect that SideEffect is suitable for.

SideEffect is suitable for updating external objects like logging, analytics, or updating a mutable state outside Compose after recomposition.

What happens when the key passed to LaunchedEffect changes?

A The composable is removed from the UI.

B Nothing, it runs only once.

C The coroutine inside <code>LaunchedEffect</code> restarts.

D The app crashes.

LaunchedEffect cancels the previous coroutine and launches a new one when the key changes.

Which of these is NOT true about SideEffect?

A It can run suspend functions.

B It is used for non-suspending side effects.

C It runs after every recomposition.

D It runs synchronously.

SideEffect cannot run suspend functions; it runs synchronously after recomposition.

Which Jetpack Compose API would you use to launch a coroutine tied to a composable's lifecycle?

A DisposableEffect

B remember

C SideEffect

D LaunchedEffect

LaunchedEffect launches coroutines that are cancelled when the composable leaves the composition.

If you want to log a message every time a composable recomposes, which API is best?

A LaunchedEffect

B SideEffect

C remember

D produceState

SideEffect runs after every recomposition, perfect for logging.

What is a key benefit of using LaunchedEffect over launching coroutines manually inside composables?

A It automatically cancels coroutines when composable leaves composition.

B It runs on the main thread only.

C It prevents recomposition.

D It disables side effects.

LaunchedEffect ties coroutine lifecycle to the composable lifecycle, cancelling coroutines when no longer needed.

Explain the difference between LaunchedEffect and SideEffect in Jetpack Compose.

Think about when and how each runs and what kind of side effects they handle.

Describe a scenario where you would use LaunchedEffect in a composable function.

Consider asynchronous tasks that depend on UI state.