Kotlin Android debounce

Question

Is there any fancy way to implement debounce logic with Kotlin Android?

I\'m not using Rx in project.

There is a way in Java, but it is too big

Answer 1

A more simple and generic solution is to use a function that returns a function that does the debounce logic, and store that in a val.

fun <T> debounce(delayMs: Long = 500L,
                   coroutineContext: CoroutineContext,
                   f: (T) -> Unit): (T) -> Unit {
    var debounceJob: Job? = null
    return { param: T ->
        if (debounceJob?.isCompleted != false) {
            debounceJob = CoroutineScope(coroutineContext).launch {
                delay(delayMs)
                f(param)
            }
        }
    }
}

Now it can be used with:

val handleClickEventsDebounced = debounce<Unit>(500, coroutineContext) {
    doStuff()
}

fun initViews() {
   myButton.setOnClickListener { handleClickEventsDebounced(Unit) }
}

Answer 2

For a simple approach from inside a ViewModel, you can just launch a job within the viewModelScope, keep track of the job, and cancel it if a new value arises before the job is complete:

private var searchJob: Job? = null

fun searchDebounced(searchText: String) {
    searchJob?.cancel()
    searchJob = viewModelScope.launch {
        delay(500)
        search(searchText)
    }
}

Answer 3

@masterwork's answer worked perfectly fine. Here it is for ImageButton with compiler warnings removed:

@ExperimentalCoroutinesApi // This is still experimental API
fun ImageButton.onClicked() = callbackFlow<Unit> {
    setOnClickListener { offer(Unit) }
    awaitClose { setOnClickListener(null) }
}

// Listener for button
val someButton = someView.findViewById<ImageButton>(R.id.some_button)
someButton
    .onClicked()
    .debounce(500) // 500ms debounce time
    .onEach {
        clickAction()
    }
    .launchIn(lifecycleScope)

Answer 4

Using tags seems to be a more reliable way especially when working with RecyclerView.ViewHolder views.

e.g.

fun View.debounceClick(debounceTime: Long = 1000L, action: () -> Unit) {
    setOnClickListener {
        when {
            tag != null && (tag as Long) > System.currentTimeMillis() -> return@setOnClickListener
            else -> {
                tag = System.currentTimeMillis() + debounceTime
                action()
            }
        }
    }
}

Usage:

debounceClick {
    // code block...
}