Why Compose is the modern UI toolkit in Android Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple Compose text element that says "Hello World".

Android Kotlin

Text(text = [1])

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

AgetString(R.string.hello)

BHello World

CR.string.hello

D"Hello World"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the text string.

Using resource IDs directly without context.

In Compose, text content must be a string literal or variable. The text must be in quotes to be a string.

2fill in blank

medium

Complete the code to create a button with a click listener in Compose.

Android Kotlin

Button(onClick = [1]) {
    Text("Click me")
}

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

AonButtonClick()

BonButtonClick

C{ onButtonClick() }

D() -> onButtonClick()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function call instead of a lambda.

Omitting the curly braces around the lambda.

The onClick parameter expects a lambda function. Wrapping the function call inside curly braces creates a lambda.

3fill in blank

hard

Fix the error in the Compose code to display a list of items using LazyColumn.

Android Kotlin

LazyColumn {
    items([1]) { item ->
        Text(text = item)
    }
}

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

AlistOf("Apple", "Banana", "Cherry")

BitemsList

Citems

DitemList()

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function call instead of a list variable.

Using an undefined variable name.

The items function expects a list variable. Use the variable name that holds the list, not a function call or undefined name.

4fill in blank

hard

Fill both blanks to create a composable function with a parameter and display it.

Android Kotlin

fun Greeting([1]: String) {
    Text(text = "Hello, [2]!")
}

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

Aname

Busername

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the parameter and inside the text.

Using undefined variables inside the text.

The parameter name and the variable used inside the text must match to display the passed value correctly.

5fill in blank

hard

Fill all three blanks to create a stateful counter button in Compose.

Android Kotlin

var count by remember { mutableStateOf([1]) }

Button(onClick = { count [2] 1 }) {
    Text(text = "Clicked [3] times")
}

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

A0

B+=

C$count

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Not initializing count to zero.

Using wrong operator for increment.

Not using string interpolation to show count.

Initialize count to 0, increment it with += 1 on click, and display the current count using $count inside the text.

Practice

1. Why is Jetpack Compose considered the modern UI toolkit for Android development?

easy

A. Because it uses simple Kotlin functions called composables to build UI

B. Because it requires XML layouts for UI design

C. Because it only supports older Android devices

D. Because it increases boilerplate code for UI

Solution

1. Step 1: Understand Compose UI building blocks

   Compose uses Kotlin functions called composables to create UI elements, making UI code simpler and more readable.

2. Step 2: Compare with traditional UI methods

   Traditional Android UI uses XML layouts, which are more verbose and separate from Kotlin code.

3. Final Answer:

   Because it uses simple Kotlin functions called composables to build UI -> Option A

4. Quick Check:

   Compose uses composables [OK]

Hint: Remember Compose uses Kotlin functions, not XML, for UI [OK]

Common Mistakes:

• Thinking Compose requires XML layouts
• Believing Compose only supports old devices
• Assuming Compose increases code complexity

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

easy

A. @Composable fun MyUI() { Text("Hello") }

B. fun MyUI() { Text("Hello") }

C. @Composable MyUI() { Text("Hello") }

D. fun @Composable MyUI() { Text("Hello") }

Solution

1. Step 1: Recall Compose function syntax

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

2. Step 2: Check each option for correct annotation placement

   @Composable fun MyUI() { Text("Hello") } correctly places @Composable before fun; others have syntax errors or misplaced annotations.

3. Final Answer:

   @Composable fun MyUI() { Text("Hello") } -> Option A

4. Quick Check:

   @Composable annotation before fun [OK]

Hint: Always put @Composable before fun keyword [OK]

Common Mistakes:

• Omitting @Composable annotation
• Placing @Composable after fun keyword
• Using incorrect function syntax

3. What will be displayed on the screen when this Compose code runs?

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

medium

A. Text showing 'Hello, World!'

B. A blank screen

C. A runtime error due to missing setContent

D. Text showing 'Hello, Compose!'

Solution

1. Step 1: Understand the composable function output

   The Greeting composable displays a Text element with the string "Hello, Compose!".

2. Step 2: Consider the code snippet's behavior

   When called inside setContent, it will render the exact text "Hello, Compose!" on screen.

3. Final Answer:

   Text showing 'Hello, Compose!' -> Option D

4. Quick Check:

   Text composable shows given string [OK]

Hint: Text composable displays the exact string passed [OK]

Common Mistakes:

• Assuming default text 'Hello, World!' is shown
• Thinking code runs without setContent
• Expecting blank screen without UI

4. Identify the error in this Compose code snippet:

@Composable
fun Welcome() {
  Text("Welcome to Compose")
  Button(onClick = { /*TODO*/ })
}

medium

A. Text composable cannot be used inside a function

B. Button requires a content parameter to display text

C. onClick lambda must return a value

D. Composable functions cannot have multiple UI elements

Solution

1. Step 1: Review Button composable usage

   Button requires a content lambda to specify what is shown inside the button, like text.

2. Step 2: Check the given code

   The Button call lacks content, so it will cause a compile error.

3. Final Answer:

   Button requires a content parameter to display text -> Option B

4. Quick Check:

   Button needs content lambda [OK]

Hint: Button always needs content inside curly braces [OK]

Common Mistakes:

• Omitting Button content lambda
• Thinking Text can't be inside composables
• Expecting onClick to return a value

5. You want to create a list of items in Compose that updates automatically when data changes. Which Compose feature helps achieve this modern UI behavior?

hard

A. Using static Text composables without recomposition

B. Using XML RecyclerView with adapters

C. Using mutableStateListOf to hold the list and observe changes

D. Using plain Kotlin lists without state management

Solution

1. Step 1: Understand Compose state management

   Compose uses state holders like mutableStateListOf to track data changes and trigger UI updates automatically.

2. Step 2: Compare options for dynamic UI updates

   Using mutableStateListOf to hold the list and observe changes uses Compose's reactive state; options A, B, and C do not support automatic UI updates in Compose.

3. Final Answer:

   Using mutableStateListOf to hold the list and observe changes -> Option C

4. Quick Check:

   Compose state holders enable auto UI updates [OK]

Hint: Use Compose state holders like mutableStateListOf for dynamic lists [OK]

Common Mistakes:

• Using XML RecyclerView in Compose projects
• Using plain lists without state triggers
• Expecting static Text to update automatically