rememberSaveable for configuration changes in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens to the state saved with rememberSaveable on screen rotation?

Consider a Compose UI using rememberSaveable to store a counter value. What will happen to the counter value when the device is rotated (causing a configuration change)?

A The app crashes because rememberSaveable cannot handle rotation.

B The counter value resets to its initial value after rotation.

C The counter value is preserved and restored after rotation.

D The counter value doubles automatically after rotation.

💡 Hint

Think about what rememberSaveable is designed to do with state during configuration changes.

rememberSaveable saves the state in a way that survives configuration changes like screen rotations, so the counter value is preserved.

📝 Syntax

intermediate

Which code snippet correctly uses rememberSaveable to save a String state?

Choose the correct Kotlin Compose code that uses rememberSaveable to save a String variable name.

A val name = remember { mutableStateOf("") }

B val name = rememberSaveable { mutableStateOf("") }

C val name = rememberSaveable("")

D val name = mutableStateOf(rememberSaveable("") )

💡 Hint

Remember the syntax for using rememberSaveable with mutableStateOf.

The correct syntax is val name = rememberSaveable { mutableStateOf("") }. Option B uses remember but not rememberSaveable, so state won't survive configuration changes. Options C and D are invalid syntax.

❓ lifecycle

advanced

What is the difference between remember and rememberSaveable regarding process death?

Which statement correctly describes how remember and rememberSaveable behave when the app process is killed by the system?

A Neither <code>remember</code> nor <code>rememberSaveable</code> can restore state after process death.

B <code>remember</code> and <code>rememberSaveable</code> both preserve state after process death automatically.

C <code>rememberSaveable</code> loses state on process death; <code>remember</code> restores it.

D <code>remember</code> loses state on process death; <code>rememberSaveable</code> can restore state if it is Parcelable or can be saved in Bundle.

💡 Hint

Think about what happens to in-memory state versus saved instance state on process death.

remember only keeps state in memory and loses it on process death. rememberSaveable saves state in a Bundle if the type is supported (e.g., Parcelable), so it can restore state after process death.

🔧 Debug

advanced

Why does this rememberSaveable state not restore after rotation?

Given this code snippet, why does the state not restore after device rotation?

var count by rememberSaveable { mutableStateOf(0) }

Button(onClick = { count++ }) {
  Text("Count: $count")
}

A Because the code uses delegated property <code>by</code> without importing <code>import androidx.compose.runtime.getValue</code> and <code>setValue</code>.

B Because the variable is declared as <code>var</code> with delegated property, it should be <code>val</code>.

C Because rememberSaveable requires a key parameter to save the state.

D Because <code>count</code> is a primitive Int, it cannot be saved by rememberSaveable.

💡 Hint

Check if the delegated property syntax is fully supported by imports.

Using by delegation requires importing getValue and setValue from Compose runtime. Without these imports, the code compiles but the state does not behave correctly.

🧠 Conceptual

expert

How does rememberSaveable handle custom data classes for state preservation?

You want to save a custom data class instance using rememberSaveable. Which approach will correctly preserve the state across configuration changes?

A Make the data class implement Parcelable or Serializable and use rememberSaveable normally.

B Use rememberSaveable without changes; all data classes are saved automatically.

C Convert the data class to JSON string manually and save that string with rememberSaveable.

D Use remember instead of rememberSaveable because rememberSaveable does not support custom classes.

💡 Hint

Think about what types rememberSaveable can save by default.

rememberSaveable can save types that are Parcelable or Serializable. To save a custom data class, it must implement one of these interfaces. Otherwise, you must provide a custom saver or convert it to a supported type.

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