Composable functions in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Composable function?

Consider this Kotlin Compose code snippet. What will be displayed on the screen?

Android Kotlin

import androidx.compose.material.Text
import androidx.compose.runtime.Composable

@Composable
fun Greeting() {
  Text(text = "Hello Compose")
}

A A runtime error due to missing setContent call

B A blank screen with no text

C A text label showing 'Hello Compose' on the screen

D A button labeled 'Hello Compose'

💡 Hint

Look at what the Text composable does inside the Greeting function.

The Greeting composable calls Text with the string 'Hello Compose', so the UI will show that text label.

❓ lifecycle

intermediate

When is a Composable function recomposed?

Given a Composable function with a state parameter, when does Compose re-run the function to update the UI?

A When the state parameter value changes

B Only once when the app starts

C Every time the user clicks anywhere on the screen

D Never, Composables run only once

💡 Hint

Think about what triggers UI updates in Compose.

Compose re-executes Composable functions when the state they depend on changes, to update the UI accordingly.

📝 Syntax

advanced

Which option correctly defines a Composable function with a parameter?

Select the correct Kotlin Compose function syntax that takes a String parameter and displays it.

A fun @Composable ShowMessage(message: String) { Text(message) }

B @Composable fun ShowMessage(message: String) { Text(text = message) }

C @Composable fun ShowMessage(message) { Text(text = message) }

D @Composable fun ShowMessage(message: String) { Text(message = message) }

💡 Hint

Remember the correct placement of the @Composable annotation and parameter types.

Option B correctly places @Composable before the function, declares the parameter type, and calls Text with text = message.

🔧 Debug

advanced

What error occurs with this Composable code?

Analyze this code snippet and identify the error it causes.

Android Kotlin

import androidx.compose.material.Text
import androidx.compose.runtime.Composable

@Composable
fun MyText() {
  Text("Hello")
}

A Compilation error: Missing @Composable annotation

B Runtime error: NullPointerException

C No error, displays 'Hello' text

D Compilation error: No value passed for parameter 'text'

💡 Hint

Check the Text composable parameter requirements.

Text requires a named parameter 'text'. Passing a string without naming causes a compilation error.

🧠 Conceptual

expert

What is the main benefit of using Composable functions in Android development?

Choose the best explanation for why Composable functions are used in modern Android UI development.

A They allow building UI declaratively and automatically update UI on state changes

B They replace all XML layouts with imperative code only

C They guarantee zero memory usage during UI rendering

D They force UI updates only when the app restarts

💡 Hint

Think about how Compose handles UI and state.

Composable functions let you describe UI declaratively and Compose handles efficient UI updates when state changes.