Quick question ```suspend fun waitForNetworkConnection = isC kotlinlang #flow

expensivebelly

12/01/2021, 9:51 AM

Quick question:

suspend fun waitForNetworkConnection() = isConnectedFlow.filter { it }.single()

isConnectedFlow

is a StateFlow, initially

false

(let’s assume we are in airplane mode in an Android app), then network connection is back,

isConnectedFlow.value = true

, however, the

waitForNetworkConnection

never ends and I don’t know why, I can see it only enters in the

filter

once and the second emission is ignored? I’ve also tried

isConnectedFlow.first { it }

to no avail. Any help would be appreciated

12/01/2021, 10:45 AM

single() waits for flow completion to ensure it's single value. You need to use

first()

isConnectedFlow.first { it }

expensivebelly

12/01/2021, 10:52 AM

no, it doesn’t

private val connectivityManager =
    context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager

  private val _isConnectedFlow = MutableStateFlow(false)

  suspend fun waitForNetworkConnection() = _isConnectedFlow.filter { it }.single()

  private val callback = object : ConnectivityManager.NetworkCallback() {
    override fun onAvailable(network: Network) {
      _isConnectedFlow.value = true
    }

    override fun onLost(network: Network) {
      _isConnectedFlow.value = false
    }

    override fun onLosing(
      network: Network,
      maxMsToLive: Int
    ) {
      _isConnectedFlow.value = false
    }

    override fun onUnavailable() {
      _isConnectedFlow.value = false
    }

    override fun onBlockedStatusChanged(
      network: Network,
      blocked: Boolean
    ) {
      _isConnectedFlow.value = !blocked
    }
  }

that’s the whole chunk of code, I’m starting to think it’s the

callback

,meaning, one is a

suspend

function and we have the

callback

emitting and the

waitForNetworkConnection

is unable to see the changes…

Because even if I do this hack:

suspend fun waitForNetworkConnection() {
    while (true) {
      val value = _isConnectedFlow.value
      if (value) break
      delay(100)
    }
  }

still does not work, _isConnectedFlow.value is always false, regardless of whether the

callback

_isConnectedFlow.value = true

never mind, it was a Dagger problem