Compose

Question 1

What is Compose used for?

Answer 1

Compose is used to develop UI in a declarative and flexible way instead of using XML.

Question 2

How does Compose simplify UI development?

Answer 2

It simplifies UI development by making it easier to manage state, handle updates efficiently, and create reusable UI elements.

Question 3

How are UI elements defined in Compose?

Answer 3

UI elements are defined as composable functions in Kotlin.

Question 4

What is declarative UI?

Answer 4

Declarative UI describes what the UI should look like, and it automatically updates when the state changes. It makes UI development more efficient and eliminates the need for manual updates.

Question 5

How is traditional UI different from declarative UI?

Answer 5

Traditional UI describes how the UI should be built, requiring manual updates when the state changes.

Question 6

What is the remember keyword used for in Compose?

Answer 6

It is used to retain data across recompositions until the composable is removed.

Question 7

What happens if you don’t use remember in a composable function?

Answer 7

Without remember, all variables inside a composable function would be created on every recomposition.

Question 8

What is Recomposition in Compose?

Answer 8

Recomposition is the process of updating the UI when the state changes.

Question 9

How does Recomposition improve efficiency in Compose?

Answer 9

Instead of recreating the entire UI, Compose only re-executes the parts that depend on the updated state, making UI updates more efficient and avoiding unnecessary recomputation.

Question 10

What is state hoisting in Compose?

Answer 10

State hoisting means that a composable doesn’t manage its own state but instead receives the state and a way to update it from its parent.

Question 11

What are the benefits of state hoisting?

Answer 11

It makes the composable stateless, more reusable, and easier to manage.

Question 12

What are side effects in Compose?

Answer 12

Side effects indicate changes to the state or other app behaviors that happen outside the scope of a composable function.

Question 13

What typically triggers side effects in Compose?

Answer 13

Side effects are typically triggered by user interactions or external events and can affect the state and UI.

Question 14

What is CompositionLocal in Compose?

Answer 14

CompositionLocal is used to pass data down the UI tree without passing it as a parameter to every composable.

Question 15

What are the benefits of CompositionLocal?

Answer 15

It helps reduce boilerplate code while keeping the data accessible only within the defined scope.

Question 16

How do you use CompositionLocal in Compose?

Answer 16

• Create a CompositionLocal variable.
• Use CompositionLocalProvider to set a value for the CompositionLocal.
• Retrieve the value using .current inside a composable.

Question 17

What is State Management in Compose?

Answer 17

Compose encourages unidirectional data flow, meaning the state flows down, events flow up, and the UI reacts to state changes.

Question 18

How does unidirectional data flow help in Compose?

Answer 18

It ensures better state control, predictability, and easier debugging by keeping state changes centralized.

Question 19

What is rememberCoroutineScope in Compose?

Answer 19

It provides a coroutine scope tied to the lifecycle of a composable, ensuring all launched coroutines are automatically canceled when the composable is destroyed.

Question 20

Why use rememberCoroutineScope?

Answer 20

It helps manage coroutines safely within a composable, preventing memory leaks and unnecessary background tasks.

Question 21

How do you convert a Flow or LiveData into a Compose state?

Answer 21

Use collectAsState for Flow and observeAsState for LiveData.

Question 22

How do you convert regular data into a Compose state?

Answer 22

Use remember with mutableStateOf.

Question 23

How do you transform asynchronous results or side effects into a Compose state?

Answer 23

Use produceState, which requires an initial value.

Question 24

How do you derive a new state from an existing state in Compose?

Answer 24

Use derivedStateOf.

Question 25

What is derivedStateOf in Compose?

Answer 25

It is used to create a state derived from another state, ensuring recomposition is triggered only when the derived state changes, not every time the original state changes.

Question 26

Why use derivedStateOf in Compose?

Answer 26

It optimizes recomposition by preventing unnecessary UI updates when the original state changes frequently but the derived state remains the same.

Question 27

What is rememberUpdatedState in Compose?

Answer 27

It is used to create a state that always refers to the latest value of another state, ensuring the latest value is used even after recomposition or inside side effects.

Question 28

When should you use rememberUpdatedState?

Answer 28

Use it when a value needs to stay up-to-date inside long-lived operations like coroutines or side effects without causing unnecessary recompositions.

Question 29

What is rememberSaveable in Compose?

Answer 29

It is used to retain state across recompositions and configuration changes by saving the state value to a bundle and restoring it when the composable is recreated.

Question 30

Why should you use rememberSaveable?

Answer 30

It helps preserve the state of a composable even when the app goes through configuration changes (like screen rotations) or recompositions.

Question 31

What happens during the initial composition of a composable?

Answer 31

The composable first enters the screen. The composer evaluates the UI tree and creates the UI elements.

Question 32

What is recomposition in Compose?

Answer 32

Recomposition happens when the state of the composable changes. Only the affected parts of the composable are recomposed, not the entire composable.

Question 33

What does skipping mean during recomposition?

Answer 33

During recomposition, if the state of the composable hasn’t changed, the composable is skipped in the process.

Question 34

What happens during the disposal phase of a composable’s lifecycle?

Answer 34

When the composable leaves the screen, it is removed from the composition.

Question 35

How do you handle lifecycle events in Compose?

Answer 35

* Launch a DisposableEffect tied to the lifecycle of the composable. * Inside the DisposableEffect, create the observer tied to the lifecycle owner to observe the lifecycle changes. * Remove the observer from the lifecycle owner in the onDispose callback for cleanup.

Question 36

How can you optimize performance in Compose?

Answer 36

Optimize performance by minimizing unnecessary recomposition, deferring expensive calculations, and using stable data types as parameters.

Question 37

How can you avoid re-executing expensive calculations in Compose?

Answer 37

Use remember to avoid re-executing expensive calculations during recompositions.

Question 38

What data types should be used as parameters in Compose to prevent unnecessary recomposition?

Answer 38

Use immutable or stable data types as parameters of a composable to prevent unnecessary recomposition.

Question 39

How can you efficiently handle large datasets in Compose?

Answer 39

Use lazy composables like LazyColumn and LazyRow for large datasets.

Question 40

Why should you specify a unique key for each item in a lazy composable?

Answer 40

Specifying a unique key helps Compose track and update the items efficiently, improving performance during recomposition.

Question 41

How can you handle frequently changing state in Compose?

Answer 41

Use lambda parameters for accessing frequently changing state to change the state read scope.

Question 42

How can lambda modifiers improve Compose performance?

Answer 42

Use lambda modifiers instead of regular modifiers to defer state reads to the layout phase or draw phase, optimizing performance.

Question 43

What is the purpose of key in Lazy Composables?

Answer 43

key is used to identify list items and reduce unnecessary recompositions for lazy composables.

Question 44

What happens if you don’t use key in a Lazy Composable when the order of a dataset changes?

Answer 44

Without a key, Compose assumes that all items have changed, causing it to recompose each item, even if only the order has changed but the items remain the same.

Question 45

How does providing a key in Lazy Composables optimize recompositions?

Answer 45

Providing a key helps Compose recognize unchanged items and avoid recomposing them, improving performance.

Question 46

Why should you wrap state read in a lambda in Compose?

Answer 46

Wrapping the state read in a lambda prevents unnecessary recompositions of unrelated composables, which would otherwise be recomposed when the state changes.

Question 47

What happens when the state changes without wrapping it in a lambda?

Answer 47

When the state changes, composables that access the state, as well as other unrelated composables at the same scope level, are recomposed.

Question 48

When should you wrap state reads in a lambda?

Answer 48

Only wrap frequently changing states because creating a lambda has some extra cost.

Question 49

Why should you use lambda modifiers instead of regular modifiers in Compose?

Answer 49

Lambda modifiers are called only in the layout or draw phase, allowing for more efficient state handling.

Question 50

How do lambda modifiers help with state changes in Compose?

Answer 50

Using lambda modifiers defers the state read to the layout or draw phase, so the entire composition gets skipped even if the state changes.

Question 51

What is the best practice for state reads in Compose?

Answer 51

Try to move the state read to the lowest possible phase to optimize performance.

Question 52

What happens during the Composition phase in Compose?

Answer 52

The Composition phase describes the UI by running composable functions.

Question 53

What happens during the Layout phase in Compose?

Answer 53

The Layout phase measures the size of UI elements and determines their placements. Layout composables and the offset lambda modifier are called in this phase.

Question 54

What happens during the Drawing phase in Compose?

Answer 54

The Drawing phase renders the UI on the screen. Canvas composables and the drawBehind lambda modifier are called in this phase.

Question 55

How does the Layout phase work in Compose?

Answer 55

Each composable measures the size of child composables (if any) and decides its own size based on these measurements, but within the constraints provided by its parent.

Question 56

What happens after the size calculation in the Layout phase?

Answer 56

After the calculation, the composable places all its child composables inside it.

Question 57

What is Unidirectional data flow in Compose?

Answer 57

Unidirectional data flow is the principle where state flows down from the parent to the child, and events flow up from the child to the parent, ensuring UI consistency and making it easier to debug.

Question 58

Why is Unidirectional data flow important in Compose?

Answer 58

It simplifies state management and makes the UI more predictable, as the flow of data and events follows a clear, one-way path.

Question 59

What is Unidirectional Flow?

Answer 59

Unidirectional Flow is a principle where data flows in a single direction, from state to UI and actions back to state, ensuring that state changes and user interactions follow a single path.

Question 60

How does Unidirectional Flow make state management easier?

Answer 60

It makes state management more predictable by ensuring that the flow of data and actions follows a clear, single path.

Question 61

What is the @Composable annotation used for?

Answer 61

The @Composable annotation is used to define a composable function in Jetpack Compose.

Question 62

Does the @Composable annotation trigger an annotation processor?

Answer 62

No, the @Composable annotation doesn’t trigger an annotation processor. It marks the function to be processed by the Compose compiler.

Question 63

Can a composable function marked with @Composable be called from other composable functions?

Answer 63

Yes, a composable function marked with @Composable can be called from other composable functions.

Question 64

What is a Composer in Jetpack Compose?

Answer 64

A Composer is used to manage the UI state and the recomposition process in Jetpack Compose.

Question 65

How does a Composer track the UI?

Answer 65

It keeps track of the order of composables to map the UI tree, which is stored as a table.

Question 66

What happens when the state changes in the Composer?

Answer 66

When the state changes, the Composer compares the differences between the new and old state and only re-executes the affected parts of the UI to update it.