NetworkStatusTracker_full.kt

class MainActivity : AppCompatActivity() {

    private val viewModel: NetworkStatusViewModel by lazy {
        ViewModelProvider(
            this,
            object : ViewModelProvider.Factory {
                override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                    val networkStatusTracker = NetworkStatusTracker(this@MainActivity)
                    return NetworkStatusViewModel(networkStatusTracker) as T
                }
            },
        ).get(NetworkStatusViewModel::class.java)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        viewModel.state.observe(this) { state ->
            findViewById<TextView>(R.id.textView).text = when (state) {
                MyState.Fetched -> "Fetched"
                MyState.Error -> "Error"
            }
        }
    }
}

sealed class MyState {
    object Fetched : MyState()
    object Error : MyState()
}

class NetworkStatusViewModel(
    networkStatusTracker: NetworkStatusTracker,
) : ViewModel() {

    val state =
        networkStatusTracker.networkStatus
            .map(
                onAvailable = { MyState.Fetched },
                onUnavailable = { MyState.Error },
            )
            .asLiveData(Dispatchers.IO)
}

sealed class NetworkStatus {
    object Available : NetworkStatus()
    object Unavailable : NetworkStatus()
}

class NetworkStatusTracker(context: Context) {

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

    val networkStatus = callbackFlow<NetworkStatus> {
        val networkStatusCallback = object : ConnectivityManager.NetworkCallback() {
            override fun onUnavailable() {
                println("onUnavailable")
                offer(NetworkStatus.Unavailable)
            }

            override fun onAvailable(network: Network) {
                println("onAvailable")
                offer(NetworkStatus.Available)
            }

            override fun onLost(network: Network) {
                println("onLost")
                offer(NetworkStatus.Unavailable)
            }
        }

        val request = NetworkRequest.Builder()
            .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
            .build()
        connectivityManager.registerNetworkCallback(request, networkStatusCallback)

        awaitClose {
            connectivityManager.unregisterNetworkCallback(networkStatusCallback)
        }
    }
}

@FlowPreview
inline fun <Result> Flow<NetworkStatus>.map(
    crossinline onUnavailable: suspend () -> Result,
    crossinline onAvailable: suspend () -> Result,
): Flow<Result> = map { status ->
    when (status) {
        NetworkStatus.Unavailable -> onUnavailable()
        NetworkStatus.Available -> onAvailable()
    }
}

@FlowPreview
inline fun <Result> Flow<NetworkStatus>.flatMap(
    crossinline onUnavailable: suspend () -> Flow<Result>,
    crossinline onAvailable: suspend () -> Flow<Result>,
): Flow<Result> = flatMapConcat { status ->
    when (status) {
        NetworkStatus.Unavailable -> onUnavailable()
        NetworkStatus.Available -> onAvailable()
    }
}