Introduction

In the world of Jetpack Compose, most UI logic is beautifully declarative. However, some operations require an imperative approach, especially when handling side effects tied to resources or APIs that need careful management. This is where `DisposableEffect` steps in as a powerful tool. With `DisposableEffect`, you can manage these imperative side effects efficiently, ensuring resources are disposed of precisely when they’re no longer needed.

In this article, we’ll dive into what `DisposableEffect` is, how it works, and when to use it effectively.

What is DisposableEffect?

`DisposableEffect` is a composable function designed to help you manage side effects linked to the lifecycle of your composable. It allows you to initialize imperative code as the composable enters the composition and clean it up as it leaves, preventing resource leaks and ensuring better performance.

Here’s an example:

@Composable
fun SampleDisposableEffect() {
    DisposableEffect(Unit) {
        // Effect initialization: like starting a listener, API call, etc.
        onDispose {
            // Clean-up code: called when composable leaves the composition
        }
    }
}

With this simple pattern, `DisposableEffect` provides a way to manage side effects like listeners, resources, or connections, offering a clean-up mechanism for when the composable leaves the composition.

When to Use DisposableEffect?

`DisposableEffect` shines in scenarios where side effects must be tied closely to the lifecycle of a composable. Here are some common use cases:

• Listeners or Callbacks: When attaching a listener to a system service, database, or UI component, `DisposableEffect` ensures that the listener is removed once the component is removed from the UI.
• Resource Management: Managing system resources like the camera, microphone, or location services. With `DisposableEffect`, you can release these resources precisely when the component is no longer active.
• API or Socket Connections: When working with WebSocket connections or API calls, `DisposableEffect` helps establish and close connections at the right times, ensuring they’re closed when the composable is out of use.

When Not to Use DisposableEffect?

While DisposableEffect is incredibly useful, there are times when it’s not the best choice. Here’s when you should avoid using DisposableEffect:

• Suspendable or Long-Running Tasks: DisposableEffect is designed for non-suspendable tasks. If your side effect requires asynchronous or suspendable work, use LaunchedEffect instead, which can handle suspending functions gracefully.
• Constant Recomposition: If the DisposableEffect key is constantly changing, this can lead to frequent disposal and re-initialization of the effect, which is inefficient. Avoid using DisposableEffect in cases where the dependency might change rapidly or unnecessarily.
• State Updates Inside DisposableEffect: Since DisposableEffect is for handling side effects, avoid updating Compose State values inside it, as this can trigger undesired recompositions and performance issues. For state updates, rely on other lifecycle-aware APIs or state management tools.
• Purely Declarative UI Logic: For UI elements that don’t require

Lifecycle of DisposableEffect

`DisposableEffect` is deeply integrated with the lifecycle of a composable. Here’s how it functions:

– When the composable enters the composition, `DisposableEffect` runs its initialization code.
– When the composable leaves the composition, the `onDispose` block is triggered, providing a precise point to release resources.

Example: Location Tracker

Consider a scenario where you’re building a location tracker. You can use `DisposableEffect` to start and stop location updates as needed.

@Composable
fun LocationTracker() {
    DisposableEffect(Unit) {
        // Start tracking location when composable enters composition
        startLocationUpdates()

        onDispose {
            // Stop tracking when composable leaves composition
            stopLocationUpdates()
        }
    }
}

In this example, `startLocationUpdates()` begins tracking as the composable appears, and `stopLocationUpdates()` halts tracking when the composable disappears, ensuring resources are managed cleanly.

Comparison with LaunchedEffect

`DisposableEffect` and `LaunchedEffect` serve different purposes:

– LaunchedEffect is intended for suspendable tasks that can be canceled if the key changes or the composable leaves the composition.
– DisposableEffect is ideal for managing non-suspendable side effects (like attaching listeners or managing resources).

Use `LaunchedEffect` when you need to handle asynchronous tasks; choose `DisposableEffect` when you need reliable setup and teardown of side effects.

Best Practices

– Avoid Heavy Logic: Since `DisposableEffect` isn’t suspendable, avoid long-running tasks within it. For asynchronous operations, pair it with `LaunchedEffect`.

– Use Keys Effectively: Be mindful of key usage. When the `DisposableEffect` key changes, the current effect is disposed of and a new one starts, so ensure your keys reflect the exact dependency you want to track.

Conclusion

`DisposableEffect` is a vital tool for managing imperative side effects in Jetpack Compose, giving you control over resource cleanup and helping avoid memory leaks or unnecessary resource usage. By integrating it into your Compose toolkit, you can ensure your composables remain efficient and cleanly manage their lifecycle.

Dobri Kostadinov
Android Consultant | Trainer
Email me | Follow me on LinkedIn | Follow me on Medium | Buy me a coffee

This article is previously published on proandroiddev.com