Скачать или смотреть Understanding the remember vs rememberUpdatedState in Jetpack Compose

Unravel the key differences between `remember` and `rememberUpdatedState` in Jetpack Compose, and learn how to use them effectively in your Android applications.
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Understanding the remember vs rememberUpdatedState in Jetpack Compose

Jetpack Compose has transformed the world of Android UI development, making it more intuitive and efficient. However, for those diving into this new paradigm, it can present some confusing concepts. One such area of confusion lies with two important functions: remember and rememberUpdatedState. In this post, we will demystify these two functions and help you understand their differences and use cases.

What is remember?

The remember function plays a crucial role in Jetpack Compose. It is designed to store values in a composable function during recompositions. Here’s a quick breakdown:

Purpose: Prevent heavy computations/operations from re-running unnecessarily when a composable is recomposed.

How it works: By utilizing remember, the variable retains its value across recompositions unless its surrounding composable is removed from the composition.

For example:

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This usage means that the variable will not be re-evaluated every time the composable re-renders unless it is recomposed due to changes in the UI.

What is rememberUpdatedState?

While remember stores values, rememberUpdatedState takes it a step further. It allows you to remember a state representation and ensure that any new values are appropriately reflected without losing the previous states.

Key Characteristics:

Purpose: Used when you want your composable to respond to changes in values without resetting the state during recompositions.

Functionality: It updates the remembered state with the latest provided value while ensuring that any “old” values are still available until they need to be replaced.

Here is the typical usage:

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How It Works:

It essentially combines the behavior of remember with the capability of triggering recomposition when the value changes.

When to Use remember versus rememberUpdatedState?

1. Use remember when:

Your variable does not need to respond immediately to state changes.

You want to avoid computations on every recomposition when the value is not changing significantly.

2. Use rememberUpdatedState when:

You need the latest value of a variable to be reflected in an ongoing computation or side-effect without running into stale references (like in lambdas or effects that need the latest input value).

Your app requires a mechanism to handle state being changed in an external or parallel operation without resetting internal state.

A Practical Example

Here’s a simple example to illustrate the difference:

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In this example:

rememberUpdatedStateInput smoothly updates with the latest input value.

rememberedInput only retains its value unless the composable necessitates recomposition.

Advanced Scenario with Lambdas

Consider a use case where you might have a landing screen that times out after a delay. You want to ensure that when the screen recomposes, any new timeout handling is used:

[[See Video to Reveal this Text or Code Snippet]]

In this scenario, even with recomposition, the delay will not restart and will correctly call the latest onTimeout function.

Conclusion

Understanding the difference between remember and rememberUpdatedState is crucial for effective UI state management in Jetpack Compose. By using these tools correctly, you can create performant, responsive applications that handle state changes gracefully. Experiment with both functions in your projects to see their effects, and you’ll soon become proficient in managing state in your Jetpack Compose apps.