Composable functions in Android Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Composable function in Jetpack Compose?

A Composable function is a special Kotlin function annotated with @Composable that describes part of the app's UI. It can be combined with other composables to build the interface.

beginner

How do you mark a function as composable in Kotlin?

By adding the @Composable annotation before the function definition.

intermediate

Why should composable functions be side-effect free and idempotent?

Because composable functions can be called many times during UI updates, they should not change data or state directly and should always produce the same UI output for the same inputs.

beginner

What is the role of the setContent function in an Android app using Compose?

It sets the UI content of an activity by calling composable functions inside it, replacing the traditional XML layout inflation.

beginner

Can composable functions call other composable functions?

Yes, composable functions can call other composable functions to build complex UI by combining smaller UI pieces.

Which annotation marks a function as composable in Jetpack Compose?

A @UIFunction

B @Composable

C @AndroidEntryPoint

D @Layout

The @Composable annotation tells the compiler that the function describes UI and can be used in Compose.

What does a composable function return?

A A View object

B A Layout XML

C Nothing (Unit)

D A Fragment

Composable functions return Unit and describe UI declaratively instead of returning View objects.

Which function is used to set the UI content in a Compose-based Android activity?

A setContent()

B setContentView()

C inflate()

D setLayout()

setContent() replaces setContentView() in Compose to set composable UI content.

Why should composable functions avoid side effects?

A To support older Android versions

B To improve app performance

C To reduce APK size

D Because they can be called multiple times during recomposition

Composable functions may be called many times during UI updates, so side effects can cause bugs or inconsistent UI.

Can composable functions have parameters?

A Yes, to customize UI based on input

B Only default parameters are allowed

C Only primitive types are allowed

D No, they cannot take parameters

Composable functions can take parameters to customize the UI they display.

Explain what a composable function is and how it is used in Jetpack Compose.

Think about how UI pieces are built in Compose.

Describe why composable functions should be side-effect free and what could happen if they are not.

Consider how UI updates happen in Compose.