Composable functions in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple composable function that displays "Hello World" text.

Android Kotlin

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

@Composable
fun Greeting() {
    Text(text = [1])
}

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

AText("Hello World")

BHello World

Ctext = "Hello World"

D"Hello World"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string

Passing the whole Text call inside Text

The Text composable requires a string argument for the text parameter. It must be a string literal with quotes.

2fill in blank

medium

Complete the code to call the Greeting composable inside another composable function.

Android Kotlin

import androidx.compose.runtime.Composable

@Composable
fun MainScreen() {
    [1]()
}

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

AText

BGreeting

CsetContent

DButton

Attempts:

3 left

💡 Hint

Common Mistakes

Calling setContent inside a composable

Using UI elements like Button or Text instead of the composable name

To display the Greeting composable inside MainScreen, you call Greeting() inside it.

3fill in blank

hard

Fix the error in the composable function by completing the code to add a parameter for the name and display it.

Android Kotlin

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

@Composable
fun Greeting(name: String) {
    Text(text = "Hello, [1]!")
}

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A$name

Buser

CName

D"name"

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the variable name inside quotes, making it a literal string

Using a different variable name not declared

To insert the parameter value inside the string, use the variable name without quotes inside the string template.

4fill in blank

hard

Fill the blank to create a composable that shows a button with a click action that updates a counter.

Android Kotlin

import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.runtime.*

@Composable
fun Counter() {
    var count by [1]
    Button(onClick = { count++ }) {
        Text(text = "Clicked: $count")
    }
}

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Aremember { mutableStateOf }

BmutableStateOf

Cremember { mutableStateOf(0) }

Dremember { mutableStateOf(0) }()

Attempts:

3 left

💡 Hint

Common Mistakes

Not using remember to keep state

Calling mutableStateOf without initial value

Incorrect lambda syntax for onClick

Use remember { mutableStateOf(0) } to create a state variable. The onClick lambda increments the count.

5fill in blank

hard

Fill all three blanks to create a composable that displays a list of names using a Column and Text composables.

Android Kotlin

import androidx.compose.foundation.layout.Column
import androidx.compose.material.Text
import androidx.compose.runtime.Composable

@Composable
fun NameList(names: List<String>) {
    Column {
        for (name in [1]) {
            Text(text = [2])
        }
    }
}

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Anames

Bname

C"name"

DnamesList

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal "name" instead of the variable

Using a wrong variable name for the list

The for loop iterates over the names list, and each Text shows the current name variable.

Practice

1. What is the main purpose of a @Composable function in Android Kotlin?

easy

A. To manage database operations

B. To handle network requests

C. To define app navigation routes

D. To build and display UI components

Solution

1. Step 1: Understand the role of @Composable

   The @Composable annotation marks functions that create UI elements in Jetpack Compose.

2. Step 2: Identify the correct purpose

   These functions are used to build and display UI components, not for networking or database tasks.

3. Final Answer:

   To build and display UI components -> Option D

4. Quick Check:

   @Composable = UI builder [OK]

Hint: Remember: @Composable means UI code [OK]

Common Mistakes:

• Thinking @Composable handles logic like networking
• Confusing @Composable with lifecycle methods
• Assuming it manages navigation or data storage

2. Which of the following is the correct way to declare a composable function in Kotlin?

easy

A. @Composable fun MyComponent() { /* UI code */ }

B. fun MyComponent() { /* UI code */ }

C. @Composable MyComponent() { /* UI code */ }

D. fun @Composable MyComponent() { /* UI code */ }

Solution

1. Step 1: Recall the syntax for composable functions

   Composable functions must be annotated with @Composable before the function keyword.

2. Step 2: Check each option

   @Composable fun MyComponent() { /* UI code */ } correctly places @Composable before fun. The other options either lack the annotation entirely or place it incorrectly (after fun or without fun).

3. Final Answer:

   @Composable fun MyComponent() { /* UI code */ } -> Option A

4. Quick Check:

   Annotation before fun = correct syntax [OK]

Hint: Always put @Composable before fun [OK]

Common Mistakes:

• Omitting the @Composable annotation
• Placing @Composable after the function name
• Using incorrect syntax like missing fun

3. What will be displayed when this composable function is called?

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

medium

A. A text label showing 'Hello, Compose!'

B. A compile-time error due to missing imports

C. An empty screen with no text

D. A button labeled 'Hello, Compose!'

Solution

1. Step 1: Understand the Text composable

   The Text composable displays a text label on the screen with the given string.

2. Step 2: Analyze the function output

   The function shows the text "Hello, Compose!" as a label, not a button or empty screen.

3. Final Answer:

   A text label showing 'Hello, Compose!' -> Option A

4. Quick Check:

   Text shows text label [OK]

Hint: Text composable always displays text on screen [OK]

Common Mistakes:

• Confusing Text with Button composable
• Assuming missing imports cause runtime error
• Expecting no output from a valid composable

4. Identify the error in this composable function:

  @Composable
  fun Welcome() {
    Text(text = Hello World)
  }

medium

A. Missing @Composable annotation

B. Missing quotes around the string in Text

C. Function name should be lowercase

D. Text composable cannot be used inside functions

Solution

1. Step 1: Check the Text parameter

   The string passed to Text must be in quotes. Here, "Hello World" is missing quotes.

2. Step 2: Verify other parts

   The function has the @Composable annotation, function name casing is allowed, and Text is valid inside composables.

3. Final Answer:

   Missing quotes around the string in Text -> Option B

4. Quick Check:

   Strings need quotes in Kotlin [OK]

Hint: Strings must be in quotes inside Text composable [OK]

Common Mistakes:

• Forgetting quotes around string literals
• Thinking function names must be lowercase
• Assuming @Composable is missing when it is present

5. How can you create a reusable composable that shows a greeting with a dynamic name?
Choose the correct function declaration:

  ?

hard

A. @Composable fun Greeting() {
Text(text = "Hello, name!")
}

B. fun Greeting(name: String) {
Text(text = "Hello, ${name}!")
}

C. @Composable fun Greeting(name: String) {
Text(text = "Hello, ${name}!")
}

D. @Composable fun Greeting(name) {
Text(text = "Hello, ${name}!")
}

Solution

1. Step 1: Check for @Composable annotation and parameter

   The function must be annotated with @Composable and accept a String parameter for the name.

2. Step 2: Verify string interpolation and parameter syntax

   @Composable fun Greeting(name: String) { Text(text = "Hello, ${name}!") } correctly uses @Composable, declares name: String, and interpolates it inside the text. The version without @Composable misses the annotation, the one without a parameter hardcodes the name, and the one missing the parameter type is invalid.

3. Final Answer:

   @Composable fun Greeting(name: String) { Text(text = "Hello, ${name}!") } -> Option C

4. Quick Check:

   Composable + typed parameter + string interpolation = correct [OK]

Hint: Composable needs annotation and typed parameters [OK]

Common Mistakes:

• Omitting @Composable annotation
• Not declaring parameter type
• Hardcoding text instead of using parameter