rememberSaveable for configuration changes in Android Kotlin

Introduction

We use rememberSaveable to keep data safe when the screen changes, like rotating the phone. It helps keep your app's state without losing it.

When you want to keep user input in a text box after rotating the device.

When you want to save a counter value during configuration changes like dark mode switch.

When you want to keep the state of a toggle button after the screen size changes.

When you want to preserve scroll position in a list after device rotation.

Syntax

Android Kotlin

val state = rememberSaveable { mutableStateOf(initialValue) }

rememberSaveable works like remember but also saves state across configuration changes.

You can use it with simple types like Int, String, Boolean, or with custom types if you provide a saver.

Examples

This saves an integer counter that survives screen rotations.

Android Kotlin

val count = rememberSaveable { mutableStateOf(0) }

This saves a string input, like a user name, across configuration changes.

Android Kotlin

val name = rememberSaveable { mutableStateOf("") }

This saves a boolean toggle state, like a checkbox, even if the device rotates.

Android Kotlin

val isChecked = rememberSaveable { mutableStateOf(false) }

Sample App

This app has a text input and a button showing how many times it was clicked. Both the typed name and click count stay the same even if you rotate the device.

Android Kotlin

import androidx.compose.foundation.layout.Column
import androidx.compose.material3.Button
import androidx.compose.material3.Text
import androidx.compose.material3.TextField
import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.rememberSaveable
import androidx.compose.ui.tooling.preview.Preview

@Composable
fun RememberSaveableExample() {
  val name = rememberSaveable { mutableStateOf("") }
  val count = rememberSaveable { mutableStateOf(0) }

  Column {
    TextField(
      value = name.value,
      onValueChange = { name.value = it },
      label = { Text("Enter your name") }
    )
    Button(onClick = { count.value++ }) {
      Text("Clicks: ${count.value}")
    }
  }
}

@Preview
@Composable
fun PreviewRememberSaveableExample() {
  RememberSaveableExample()
}

Important Notes

rememberSaveable automatically saves simple types like Int, String, and Boolean.

For complex objects, you need to provide a custom saver to rememberSaveable.

This helps avoid losing user data during common changes like screen rotation or language change.

Summary

rememberSaveable keeps your UI state safe during configuration changes.

Use it for user inputs, counters, toggles, and other simple states.

It works like remember but adds automatic saving and restoring.

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