Debounce Mutation State Policy

Author: Pablisco

This is an alternate method of debouncing state changes in Jetpack Compose.

Using this technique, you can leverage a custom SnapshotMutationPolicy to accomplish the same debouncing behavior. The main difference is that this approach uses the default mutableStateOf implementation with a custom mutation policy instead.


/**
 * Returns a [SnapshotMutationPolicy] implementation that applies a debounce mechanism to mutation events.
 *
 * @param debounceTime The time window in milliseconds within which mutation events are considered to be the same.
 * @return An instance of [SnapshotMutationPolicy] that applies a debounce mechanism.
 *
 * @param T The type of the snapshot.
 */
fun <T> debounceMutationPolicy(
    debounceTime: Long = 500,
): SnapshotMutationPolicy<T> = object : SnapshotMutationPolicy<T> {
    var lastUpdate = 0L
    override fun equivalent(a: T, b: T): Boolean = checkEquivalence(a, b).also { updateIfNeeded() }
    private fun updateIfNeeded() = apply { if (isUpdateTime()) lastUpdate = now() }
    private fun checkEquivalence(a: T, b: T): Boolean = if (isUpdateTime()) a == b else CancelMutation
    private fun isUpdateTime() = now() - lastUpdate > debounceTime
}

/**
 * Determines whether a mutation should be canceled or not.
 *
 * The value of this property determines whether a mutation should be canceled or not based on the conditions defined
 * in the "checkEquivalence" function.
 * If CancelMutation is set to `true`, the "checkEquivalence" function will return `true` if the time between the last
 * update and the current time is greater than the debounce time.
 *
 * Otherwise, it will return the result of the equality comparison between the two provided values.
 */
private const val CancelMutation = true

It’s a great reminder that in coding, flexibility is key. Whether you choose to extend MutableState or use a custom mutation policy, you’ve got options to tailor your state management to your needs.

📎 View original gist on GitHub

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