Why and How to Use rememberSaveable in Jetpack Compose

Jetpack Compose, Google’s modern toolkit for building native Android UIs, introduces a variety of powerful tools and paradigms that simplify UI development. Among these tools, remember and rememberSaveable stand out as crucial for managing state in a Compose application. While remember is excellent for retaining state across recompositions, rememberSaveable provides an extra layer of persistence by retaining state across configuration changes like screen rotations or process deaths.

In this post, we’ll dive deep into the why and how of using rememberSaveable in Jetpack Compose. By the end, you’ll have a solid understanding of its role, implementation details, and best practices for using it effectively in real-world applications.

Understanding State in Jetpack Compose

State management is a fundamental concept in Jetpack Compose. The UI in Compose reacts to state changes, which means managing state correctly is crucial for building dynamic and resilient applications.

The Role of remember

The remember function is used to retain state across recompositions. For example:

var counter by remember { mutableStateOf(0) }

Button(onClick = { counter++ }) {
    Text(text = "Clicked $counter times")
}

Here, the counter value persists across recompositions of the Button composable. However, if the user rotates the screen or the activity is recreated, the counter value resets to 0. This is where rememberSaveable becomes essential.

The Need for rememberSaveable

Android’s Activity lifecycle and Compose’s state management don’t inherently handle state persistence across configuration changes. rememberSaveable steps in to fill this gap by:

  • Retaining state across configuration changes (e.g., screen rotations).

  • Utilizing mechanisms like the SavedStateHandle under the hood to persist state even if the process is killed and restored.

Using rememberSaveable

Basic Usage

To retain state across configuration changes, replace remember with rememberSaveable:

var counter by rememberSaveable { mutableStateOf(0) }

Button(onClick = { counter++ }) {
    Text(text = "Clicked $counter times")
}

Now, even if the screen is rotated, the counter value remains intact.

How It Works

Under the hood, rememberSaveable uses the Android SavedStateRegistry to store and restore state. It automatically saves state for types like:

  • Primitive types (e.g., Int, String)

  • Collections (e.g., List, Map)

  • Parcelable objects

For unsupported types, you can provide a custom Saver.

Advanced Concepts: Custom Savers

Not all data types are inherently supported by rememberSaveable. For unsupported types, you can define a Saver to handle serialization and deserialization.

Example: Using a Custom Saver

Consider a scenario where you need to persist a complex object:

data class User(val id: Int, val name: String)

val UserSaver = Saver<User, Map<String, Any>>(
    save = { user -> mapOf("id" to user.id, "name" to user.name) },
    restore = { map -> User(map["id"] as Int, map["name"] as String) }
)

var user by rememberSaveable(saver = UserSaver) { mutableStateOf(User(1, "John Doe")) }

Text(text = "User: ${user.name}")

Here, the Saver ensures that the User object is stored and restored correctly.

Built-in Savers

Jetpack Compose provides built-in Saver implementations for commonly used types like Parcelable objects. Simply annotate your custom class with @Parcelize, and rememberSaveable will handle it automatically:

@Parcelize
data class User(val id: Int, val name: String) : Parcelable

var user by rememberSaveable { mutableStateOf(User(1, "John Doe")) }

Best Practices for rememberSaveable

  1. Use rememberSaveable for UI State: Only use it for state directly tied to the UI and that needs to persist across configuration changes. For other types of state, consider ViewModel or Repository layers.

  2. Avoid Overusing Custom Savers: While custom savers are powerful, overusing them for complex objects can lead to increased serialization complexity and potential performance issues. Use ViewModel for more complex state management needs.

  3. Combine with ViewModel: For apps with complex data layers, combine rememberSaveable with ViewModel to maintain a balance between UI state persistence and app-wide state management.

  4. Optimize Performance: Avoid saving large objects or collections directly. Instead, store identifiers or minimal data needed to restore the state.

  5. Test Thoroughly: Ensure state persistence works correctly across all scenarios, including process deaths and multi-window mode.

Common Pitfalls

  1. Misusing rememberSaveable: Using rememberSaveable for non-UI state can lead to bloated SavedStateRegistry usage. Stick to lightweight, UI-specific state.

  2. Ignoring Unsupported Types: Forgetting to define a Saver for unsupported types can result in runtime errors.

  3. Overlooking Process Deaths: Test your app for process death scenarios to ensure state restoration works seamlessly.

Real-World Use Cases

Form Data Persistence

Imagine a form with multiple input fields. Using rememberSaveable, you can persist the entered data across screen rotations:

var name by rememberSaveable { mutableStateOf("") }
var email by rememberSaveable { mutableStateOf("") }

Column {
    TextField(value = name, onValueChange = { name = it }, label = { Text("Name") })
    TextField(value = email, onValueChange = { email = it }, label = { Text("Email") })
}

Tab Navigation

For a multi-tab UI, rememberSaveable can retain the selected tab across configuration changes:

val tabs = listOf("Home", "Profile", "Settings")
var selectedTabIndex by rememberSaveable { mutableStateOf(0) }

TabRow(selectedTabIndex = selectedTabIndex) {
    tabs.forEachIndexed { index, tab ->
        Tab(
            selected = selectedTabIndex == index,
            onClick = { selectedTabIndex = index },
            text = { Text(tab) }
        )
    }
}

Conclusion

rememberSaveable is a powerful tool for managing UI state in Jetpack Compose, especially when dealing with configuration changes. By understanding its workings and leveraging its capabilities effectively, you can build resilient and user-friendly Android applications.

When combined with other state management tools like ViewModel, rememberSaveable ensures your Compose-based apps remain robust, maintainable, and performant.

Experiment with rememberSaveable in your projects and unlock the full potential of Jetpack Compose!

Ready to dive deeper into Jetpack Compose? Check out our advanced guides and tutorials to take your skills to the next level!