rememberSaveable for configuration changes in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save the state of the counter across configuration changes using rememberSaveable.

Android Kotlin

var counter by [1] { mutableStateOf(0) }

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

AstateOf()

BrememberSaveable()

CmutableStateOf()

Dremember()

Attempts:

3 left

💡 Hint

Common Mistakes

Using remember() instead of rememberSaveable() causes state loss on rotation.

Using mutableStateOf() alone does not save state across configuration changes.

Using rememberSaveable() ensures the counter value is saved and restored across configuration changes like screen rotations.

2fill in blank

medium

Complete the code to create a button that increments the counter saved with rememberSaveable.

Android Kotlin

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

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

A+=

B*=

C-=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using -= decreases the counter instead of increasing it.

Using *= or /= changes the value incorrectly.

The += operator increases the counter by 1 each time the button is clicked.

3fill in blank

hard

Fix the error in the code to properly save a String state across configuration changes.

Android Kotlin

var name by [1] { mutableStateOf("") }

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

AmutableStateOf()

Bremember()

CrememberSaveable()

Dstate()

Attempts:

3 left

💡 Hint

Common Mistakes

Using remember() causes the state to reset on rotation.

Using mutableStateOf() alone does not save state across configuration changes.

rememberSaveable() is needed to save the String state across configuration changes, unlike remember().

4fill in blank

hard

Fill both blanks to create a rememberSaveable state for a Boolean flag and toggle it on button click.

Android Kotlin

var isChecked by [1] { mutableStateOf(false) }
Button(onClick = { isChecked = ![2] }) {
    Text("Toggle")
}

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

ArememberSaveable()

BisChecked

Cremember()

Dflag

Attempts:

3 left

💡 Hint

Common Mistakes

Using remember() instead of rememberSaveable() loses state on rotation.

Negating the wrong variable name causes errors.

The Boolean state isChecked is saved with rememberSaveable() and toggled by negating its current value.

5fill in blank

hard

Fill all three blanks to create a rememberSaveable state for a String, update it on text input, and display it.

Android Kotlin

var text by [1] { mutableStateOf("") }
TextField(value = [2], onValueChange = { [3] = it })
Text(text = text)

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

ArememberSaveable()

Btext

Dremember()

Attempts:

3 left

💡 Hint

Common Mistakes

Using remember() loses state on configuration changes.

Not updating the correct variable on input change.

The String state text is saved with rememberSaveable(), updated on input change, and displayed below.

Practice

1. What is the main purpose of rememberSaveable in Jetpack Compose?

easy

A. To save UI state across configuration changes like screen rotations

B. To permanently store data in a database

C. To create animations in the UI

D. To manage network requests efficiently

Solution

1. Step 1: Understand configuration changes

   Configuration changes like screen rotation cause the UI to be recreated, losing normal state.

2. Step 2: Role of rememberSaveable

   rememberSaveable automatically saves and restores simple UI state during these changes.

3. Final Answer:

   To save UI state across configuration changes like screen rotations -> Option A

4. Quick Check:

   rememberSaveable = saves state on config changes [OK]

Hint: RememberSaveable = remember + auto save/restore state [OK]

Common Mistakes:

• Confusing rememberSaveable with permanent storage
• Thinking it manages animations or network
• Using remember instead and losing state on rotation

2. Which of the following is the correct syntax to declare a counter state that survives configuration changes using rememberSaveable?

easy

A. var count = mutableStateOf(0)

B. val count = remember { mutableStateOf(0) }

C. var count by rememberSaveable { mutableStateOf(0) }

D. val count by rememberSaveable(0)

Solution

1. Step 1: Identify correct usage of rememberSaveable

   The correct syntax uses delegation with by and initializes with mutableStateOf inside a lambda.

2. Step 2: Check each option

   var count by rememberSaveable { mutableStateOf(0) } matches the correct pattern: var count by rememberSaveable { mutableStateOf(0) }.

3. Final Answer:

   var count by rememberSaveable { mutableStateOf(0) } -> Option C

4. Quick Check:

   rememberSaveable needs mutableStateOf inside lambda [OK]

Hint: Use var count by rememberSaveable { mutableStateOf(0) } [OK]

Common Mistakes:

• Using remember instead of rememberSaveable
• Missing delegation with 'by'
• Passing initial value directly without lambda

3. Given this code snippet, what will be the displayed count after rotating the device twice?

var count by rememberSaveable { mutableStateOf(0) }
Button(onClick = { count++ }) {
  Text("Count: $count")
}

medium

A. App crashes on rotation due to state loss

B. Count resets to 0 after each rotation

C. Count increments automatically on rotation

D. Count value is preserved across rotations

Solution

1. Step 1: Understand rememberSaveable behavior

   It saves and restores the state value across configuration changes like rotations.

2. Step 2: Analyze the code

   Count increments on button clicks and is preserved after rotations, so it does not reset.

3. Final Answer:

   Count value is preserved across rotations -> Option D

4. Quick Check:

   rememberSaveable preserves state on rotation [OK]

Hint: rememberSaveable keeps count after rotations [OK]

Common Mistakes:

• Assuming count resets after rotation
• Thinking rotation increments count
• Believing app crashes due to state loss

4. What is wrong with this code if the goal is to preserve the toggle state across configuration changes?

val isChecked = remember { mutableStateOf(false) }
Checkbox(checked = isChecked.value, onCheckedChange = { isChecked.value = it })

medium

A. The onCheckedChange lambda is missing

B. Using remember instead of rememberSaveable loses state on rotation

C. Checkbox requires a String value, not Boolean

D. MutableStateOf should not be used for checkboxes

Solution

1. Step 1: Identify state preservation method

   Using remember alone does not save state across configuration changes.

2. Step 2: Correct approach

   Replace remember with rememberSaveable to preserve toggle state on rotation.

3. Final Answer:

   Using remember instead of rememberSaveable loses state on rotation -> Option B

4. Quick Check:

   rememberSaveable needed for state preservation [OK]

Hint: Use rememberSaveable, not remember, for config change state [OK]

Common Mistakes:

• Confusing remember with rememberSaveable
• Thinking mutableStateOf is wrong for checkbox
• Missing onCheckedChange lambda

5. You want to save a user input text that should survive configuration changes and process death. Which approach correctly uses rememberSaveable with a custom saver for a complex data type?

hard

A. var userInput by rememberSaveable(stateSaver = TextFieldValue.Saver) { mutableStateOf(TextFieldValue("") ) }

B. var userInput by rememberSaveable { mutableStateOf(TextFieldValue("") ) }

C. var userInput by remember { mutableStateOf(TextFieldValue("") ) }

D. var userInput by rememberSaveable(TextFieldValue("") )

Solution

1. Step 1: Understand saving complex types

   Complex types like TextFieldValue need a custom saver to be saved/restored by rememberSaveable.

2. Step 2: Check correct syntax

   var userInput by rememberSaveable(stateSaver = TextFieldValue.Saver) { mutableStateOf(TextFieldValue("") ) } uses stateSaver = TextFieldValue.Saver with rememberSaveable and mutableStateOf, which is correct.

3. Final Answer:

   var userInput by rememberSaveable(stateSaver = TextFieldValue.Saver) { mutableStateOf(TextFieldValue("") ) } -> Option A

4. Quick Check:

   Custom saver needed for complex types with rememberSaveable [OK]

Hint: Use stateSaver parameter for complex types in rememberSaveable [OK]

Common Mistakes:

• Not providing a custom saver for complex types
• Using remember instead of rememberSaveable
• Passing initial value directly without lambda