Android EditText Coroutine debounce operator like RxJava

Question

I need to make EditText with autosuggest functionality and I need to listen to its input. I also need to ignore EditText change when it is set programmatically.

Wondering if there is solution to make debounce EditText with Coroutines without using delay in this situation.

Answer 1

Turn text change event to a Flow

Use kotlinx.coroutines 1.5.0

@ExperimentalCoroutinesApi
@CheckResult
fun EditText.textChanges(): Flow<CharSequence?> {
  return callbackFlow<CharSequence?> {
    val listener = object : TextWatcher {
      override fun afterTextChanged(s: Editable?) = Unit
      override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit
      override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
        trySend(s)
      }
    }
    addTextChangedListener(listener)
    awaitClose { removeTextChangedListener(listener) }
  }.onStart { emit(text) }
}

If using androidx.core.widget.doOnTextChanged:

@ExperimentalCoroutinesApi
@CheckResult
fun EditText.textChanges(): Flow<CharSequence?> {
  return callbackFlow {
    checkMainThread()

    val listener = doOnTextChanged { text, _, _, _ -> trySend(text) }
    awaitClose { removeTextChangedListener(listener) }
  }.onStart { emit(text) }
}

Use:

editText.textChanges().debounce(300)
    .onEach { ... }
    .launchIn(lifecycleScope)

And something like this:

fun executeSearch(term: String): Flow<SearchResult> { ... }

editText.textChanges()
    .filterNot { it.isNullOrBlank() } 
    .debounce(300)
    .distinctUntilChanged()
    .flatMapLatest { executeSearch(it) }
    .onEach { updateUI(it) }
    .launchIn(lifecycleScope)

Source code: https://github.com/Kotlin-Android-Open-Source/MVI-Coroutines-Flow/blob/master/core-ui/src/main/java/com/hoc/flowmvi/core_ui/FlowBinding.kt#L116

Answer 2

After doing some research on Coroutines and Flow I came up with solution on creating custom EditText which holds debounce logic inside it and enables me to attach debounce TextWatcher and remove it when I want. Here is the code of my solution

class DebounceEditText @JvmOverloads constructor(
    context: Context,
    attributeSet: AttributeSet? = null,
    defStyleAttr: Int = 0
) : AppCompatEditText(context, attributeSet, defStyleAttr) {

    private val debouncePeriod = 600L
    private var searchJob: Job? = null

    @FlowPreview
    @ExperimentalCoroutinesApi
    fun setOnDebounceTextWatcher(lifecycle: Lifecycle, onDebounceAction: (String) -> Unit) {
        searchJob?.cancel()
        searchJob = onDebounceTextChanged()
            .debounce(debouncePeriod)
            .onEach { onDebounceAction(it) }
            .launchIn(lifecycle.coroutineScope)
    }

    fun removeOnDebounceTextWatcher() {
        searchJob?.cancel()
    }

    @ExperimentalCoroutinesApi
    private fun onDebounceTextChanged(): Flow<String> = channelFlow {
        val textWatcher = object : TextWatcher {
            override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

            override fun onTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {}

            override fun afterTextChanged(p0: Editable?) {
                offer(p0.toString())
            }
        }

        addTextChangedListener(textWatcher)

        awaitClose {
            removeTextChangedListener(textWatcher)
        }
    }
}

When I want to activate Debounce TextWatcher, I just call

// lifecycle is passed from Activity/Fragment lifecycle, because we want to relate Coroutine lifecycle with the one DebounceEditText belongs   
debounceEditText.setOnDebounceTextWatcher(lifecycle) { input ->
    Log.d("DebounceEditText", input)
}

I had problem with focus when implementing DebounceEditText inside xml, so I had to set clickable, selectable and focusableInTouchMode to true.

    android:focusable="true"
    android:focusableInTouchMode="true"
    android:clickable="true"

In case I want to set input in DebounceEditText without triggering, just remove TextWatcher by calling

debounceEditText.removeOnDebounceTextWatcher()