A Debouncing LiveData helper

DebounceLiveData.kt

class DebounceLiveData<Source>(
    private val source: LiveData<Source>,
    private val debounceMs: Long
) : LiveData<Source>(), CoroutineScope {
    private val job = SupervisorJob()
    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job
    private var debounceJob: Job? = null

    private val observer = Observer<Source> { source ->
        debounceJob?.cancel()
        debounceJob = launch {
            delay(debounceMs)
            value = source
        }
    }

    override fun onActive() {
        source.observeForever(observer)
    }

    override fun onInactive() {
        debounceJob?.cancel()
        source.removeObserver(observer)
    }
}

fun <Source> LiveData<Source>.debounce(
    time: Long,
    unit: TimeUnit = TimeUnit.MILLISECONDS
): LiveData<Source> {
    val timeMs = when (unit) {
        TimeUnit.NANOSECONDS -> unit.toMillis(time)
        TimeUnit.MICROSECONDS -> unit.toMillis(time)
        TimeUnit.MILLISECONDS -> time
        TimeUnit.SECONDS -> unit.toMillis(time)
        TimeUnit.MINUTES -> unit.toMillis(time)
        TimeUnit.HOURS -> unit.toMillis(time)
        TimeUnit.DAYS -> unit.toMillis(time)
    }

    return DebounceLiveData(this, timeMs)
}

Sample.kt

// Imagine you have an EditText and it emits its value (via OnQueryTextListener) to a LiveData
// Now you can debounce it to do a search.

class SearchViewModel(//depencencies) : ViewModel() {
  val query: MutableLiveData<String>()

  val searchResults: LiveData<List<SearchResult>>
    get() = query.debounce(200).filter { it.lenght > 3 }.asyncMap { query ->
      api.search(query) // Returns List<SearchResult>
    }
}

class SearchFragment : Fragment() {
  override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    viewModel.searchResults.observe(viewLifecycleOwner, Observer { searchResults ->
      // deal with search results
    })

    search_view.setOnQueryTextListener(object : SearchView.OnQueryTextListener {
      override fun onQueryTextChange(newText: String): Boolean {
        viewModel.query.value = newText
        return false
      }
    })
  }
}