Quick question: ```suspend fun waitForNetworkConnection() = isConnectedFlow.filter { it }.single()``...

# flow

[expensivebelly]

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

[bezrukov]

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

isConnectedFlow.first { it }

should work

[expensivebelly]

no, it doesn’t

[expensivebelly]

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
    }
  }

[expensivebelly]

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…

[expensivebelly]

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 has called _isConnectedFlow.value = true

[expensivebelly]

never mind, it was a Dagger problem