Button composable in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple Button with text "Click me".

Android Kotlin

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

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

AonClick()

B() -> Unit {}

C{}

DclickListener

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for the lambda.

Passing a function call instead of a lambda.

The onClick parameter expects a lambda function. An empty lambda is written as {}.

2fill in blank

medium

Complete the code to display a Button with the text "Submit".

Android Kotlin

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

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

AcontentDescription

Btext

Clabel

Dtitle

Attempts:

3 left

💡 Hint

Common Mistakes

Using contentDescription instead of text.

Using label or title which are not valid parameters here.

The Text composable uses the text parameter to show the string inside.

3fill in blank

hard

Fix the error in the Button composable by completing the onClick lambda correctly.

Android Kotlin

Button(onClick = [1]) {
    Text(text = "Press")
}

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

A{ println("Pressed") }

Bfun() { println("Pressed") }

Cprintln("Pressed")

D() -> println("Pressed")

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function call without braces causing a syntax error.

Using incorrect lambda syntax like fun().

The onClick expects a lambda expression. The correct syntax is { println("Pressed") }.

4fill in blank

hard

Fill both blanks to create a Button with a click action that prints "Clicked" and text "Tap me".

Android Kotlin

Button(onClick = [1]) {
    Text(text = [2])
}

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

A{ println("Clicked") }

B"Tap me"

C"Click me"

D() -> println("Clicked")

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for the lambda.

Passing the wrong string to the Text composable.

The onClick needs a lambda with curly braces. The Text composable needs a string for the text parameter.

5fill in blank

hard

Fill all three blanks to create a Button with onClick printing "Hello", text "Go", and a Modifier to add padding.

Android Kotlin

Button(onClick = [1], modifier = [2]) {
    Text(text = [3])
}

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

A{ println("Hello") }

BModifier.padding(16.dp)

C"Go"

DModifier.fillMaxWidth()

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use curly braces for the lambda.

Using the wrong Modifier function.

Not putting the text string in quotes.

The onClick needs a lambda with curly braces. The modifier uses Modifier.padding(16.dp) to add space. The Text composable needs a string for the text parameter.

Practice

1. What is the main purpose of a Button composable in Android Jetpack Compose?

easy

A. To show lists of items

B. To display images on the screen

C. To create text input fields

D. To let users tap and trigger actions

Solution

1. Step 1: Understand the role of Button composable

   The Button composable is designed to be tapped by users to perform an action.

2. Step 2: Compare with other UI elements

   Other options like displaying images or text input are done by different composables, not Button.

3. Final Answer:

   To let users tap and trigger actions -> Option D

4. Quick Check:

   Button = triggers actions on tap [OK]

Hint: Buttons are for user taps that do something [OK]

Common Mistakes:

• Confusing Button with Image or TextField
• Thinking Button displays content only
• Assuming Button is for layout only

2. Which of the following is the correct syntax to create a Button with a label "Click Me" in Jetpack Compose?

easy

A. Button(onClick = { Text("Click Me") })

B. Button { onClick = { } Text("Click Me") }

C. Button(onClick = { }) { Text("Click Me") }

D. Button(Text("Click Me"), onClick = { })

Solution

1. Step 1: Recall Button syntax in Compose

   The Button composable takes an onClick lambda and a content lambda for the label.

2. Step 2: Check each option

   Button(onClick = { }) { Text("Click Me") } correctly places onClick and Text inside Button's trailing lambda. Others misuse syntax or parameter order.

3. Final Answer:

   Button(onClick = { }) { Text("Click Me") } -> Option C

4. Quick Check:

   Button(onClick) { Text } syntax [OK]

Hint: Button(onClick) { Text("label") } is correct pattern [OK]

Common Mistakes:

• Putting onClick inside Button's content lambda
• Passing Text as a parameter instead of inside lambda
• Wrong order or missing braces

3. What will be displayed when this code runs?

Button(onClick = { println("Tapped") }) {
  Text("Press Here")
}

medium

A. A text label "Press Here" with no button functionality

B. A button labeled "Press Here" that prints "Tapped" when clicked

C. A button labeled "Tapped" that prints "Press Here" when clicked

D. An error because println cannot be used inside onClick

Solution

1. Step 1: Identify the Button label

   The Button shows the Text composable with label "Press Here".

2. Step 2: Understand onClick behavior

   When tapped, the onClick lambda runs println("Tapped"), printing to console.

3. Final Answer:

   A button labeled "Press Here" that prints "Tapped" when clicked -> Option B

4. Quick Check:

   Button label = "Press Here", onClick prints "Tapped" [OK]

Hint: Button label is Text; onClick runs code inside braces [OK]

Common Mistakes:

• Confusing label text with printed output
• Thinking println causes UI error
• Assuming onClick changes label text

4. This code tries to create a Button but causes a compile error:

Button(onClick = println("Clicked")) {
  Text("Tap")
}

What is the error?

medium

A. onClick expects a lambda, but println("Clicked") is called immediately

B. Text composable cannot be inside Button

C. Button requires a label parameter, missing here

D. onClick cannot print text

Solution

1. Step 1: Analyze onClick parameter

   onClick expects a lambda () -> Unit, but println("Clicked") is a function call executed immediately.

2. Step 2: Understand correct lambda usage

   It should be onClick = { println("Clicked") } to pass a lambda that runs println when clicked.

3. Final Answer:

   onClick expects a lambda, but println("Clicked") is called immediately -> Option A

4. Quick Check:

   onClick needs lambda, not immediate call [OK]

Hint: Use curly braces {} for onClick lambda, not direct call [OK]

Common Mistakes:

• Calling function instead of passing lambda
• Misunderstanding onClick parameter type
• Thinking Text inside Button causes error

5. You want a Button that disables itself after being clicked once. Which approach correctly implements this behavior?

hard

A. Use a state variable to track clicks and set enabled = false after first click

B. Call Button(enabled = false) directly without state

C. Put enabled = false inside onClick lambda

D. Use Text composable with onClick instead of Button

Solution

1. Step 1: Understand Button enabled property

   The Button composable has an enabled parameter to control if it can be clicked.

2. Step 2: Use state to track clicks

   To disable after first click, use a state variable that changes on click and updates enabled.

3. Step 3: Evaluate options

   Use a state variable to track clicks and set enabled = false after first click correctly uses state to disable button after click. Others ignore state or misuse enabled.

4. Final Answer:

   Use a state variable to track clicks and set enabled = false after first click -> Option A

5. Quick Check:

   State controls enabled to disable button after click [OK]

Hint: Use state to toggle enabled property after click [OK]

Common Mistakes:

• Setting enabled false without state causes permanent disable
• Trying to disable inside onClick without state
• Using Text instead of Button for clickable UI