RememberSaveable in Jetpack Compose
Tags: android
Published: 2024-01-02 07:36:46



In the realm of Jetpack Compose, where UIs are dynamic and recompositions reign supreme, preserving state across configuration changes is crucial. Enter the valiant knight `rememberSaveable`, ready to protect your precious state from the perils of screen rotations, window resizing, and even process death!

But what exactly is this noble companion, and how can you wield its power effectively?

Understanding `rememberSaveable`:

- **State Preservation:** It ensures that values calculated within a composable survive configuration changes, maintaining UI consistency and preventing data loss.
- **Teamwork with Saver's**: It works hand-in-hand with `Saver` objects to handle the intricate details of saving and restoring various data types.
- **Avoiding Recalculations:** It saves you from unnecessary recalculations during recompositions, boosting performance and improving user experience.

**How to Harness Its Power:**

1. **Import the Essential:** Begin by importing `rememberSaveable` from `androidx.compose.runtime`:
   ```kotlin
   import androidx.compose.runtime.rememberSaveable
   ```

2. **Call for Assistance:** Use `rememberSaveable` within a composable, providing a `Saver` (if needed) and a calculation lambda:
   ```kotlin
   val mySavedValue = rememberSaveable(saver = mySaver) {
       // Perform calculations or create a value here
   }
   ```

**Example in Action:**

```kotlin
//A Persistent Counter Sample:
var count by rememberSaveable { mutableStateOf(0) }

Button(onClick = { count++ }) {
    Text("Count: $count")
}
```
**Even if the screen rotates, the button's counter persists!**

**Saving Custom Data with `listSaver`:**

- For lists, use `listSaver` to handle their state preservation:
   ```kotlin
   val myList = rememberSaveable(saver = listSaver(save = { ... }, restore = { ... })) {
       mutableStateListOf<MyDataClass>()
   }
   ```

### Pros of `rememberSaveable`:
* **State persistence across configuration changes:** Unlike `remember`, which only retains state across recompositions, `rememberSaveable` saves state even when the activity or fragment recreates (e.g., on rotation, split-screen, or process death). This ensures a seamless user experience where data won't be lost during these events.
* **Simple and concise syntax:** Using `rememberSaveable` is straightforward and follows the same pattern as `remember`, making it easy to adopt and integrate into your Compose code.
* **Automatic saving for basic types:** For primitive types and built-in classes like strings and collections, `rememberSaveable` handles the saving process automatically using Bundles.
* **Custom saving support:** For more complex data types, you can provide a custom saver object to handle the serialization and deserialization process, giving you fine-grained control over state persistence.
* **Improved user experience:** By preventing data loss and maintaining consistent state across configuration changes, `rememberSaveable` enhances the user experience and makes your app feel more polished and reliable.


### Cons of `rememberSaveable`:

* **Performance impact:** Saving and restoring large or complex state objects can impact performance and slow down UI updates. Consider using other state management techniques (e.g., ViewModels) for such cases.
* **Bundle size limitations:** Bundles have size limitations, so storing excessive data in `rememberSaveable` can lead to crashes. Be mindful of what you save and avoid large objects or extensive collections.
* **Potential data inconsistency:** If your saved state relies on external data sources or other dynamic elements, it might become inconsistent upon restoration if those sources change during the configuration change.
* **Increased complexity for custom savers:** Implementing custom savers adds complexity to your code and requires a deeper understanding of data serialization and deserialization processes.

Overall, `rememberSaveable` is a powerful tool for state persistence in Jetpack Compose, but it's important to weigh its pros and cons carefully and consider alternatives when dealing with large data or complex scenarios.


Here are some additional tips:

- Use `rememberSaveable` selectively for only the state that truly needs to persist across configuration changes.
- Optimize your custom savers for performance and efficiency.
- Monitor your app's performance when using `rememberSaveable` to avoid any potential bottlenecks.
- `rememberSaveable` is a powerful tool for state preservation in Compose.
- Use it with `Saver`s for custom data types and lists.
- It enhances UI consistency and performance.
- Explore other built-in Savers like `mapSaver` and `setSaver`.
- Consider creating custom Savers for complex state management.


By understanding the advantages and drawbacks, you can leverage `rememberSaveable` effectively and create robust and responsive Compose UIs.

So, fellow developers, embrace `rememberSaveable` and create Compose apps with resilient state that gracefully handles any configuration change thrown its way!