Hi, What is best way to detect "No Internet connec...

# android

[Kulwinder Singh]

Hi, What is best way to detect "No Internet connection" using Retrofit + Coroutines, currently i have added interceptor

private val realInterceptor = Interceptor { chain ->
        if (!NetworkConnection.getInstance().isConnected) {
            throw NoInternetException()
        }
	/..../
    }

but to work with this i have to add try/catch block on every request, there are so many requests. Below is sample of how i'm handling each network request->

val response = apiService.getItems().toNetworkResult()
        when (response) {
            is NetworkResult.Success -> onDataLoaded(response.data)
            is NetworkResult.Error -> toast(response.errorCode)
        }

and this is how toNetworkResult looks like

fun <T : Any> Response<T>.toNetworkResult(): NetworkResult<T> {
    val response = this
    if (response.isSuccessful)
        return NetworkResult.Success(response.body()!!)

    val error = GsonUtils.toObject<ErrorResponse>(response.errorBody()!!.string())
    return NetworkResult.Error(response.code(), error)
}

I just want to know if it is possible to handle it inside toNetworkResult() or any other similar solution i can implement, where i don't have to add try/catch on every request

[gildor]

if (!NetworkConnection.getInstance().isConnected) {
            throw NoInternetException()
        }

[gildor]

this approach is just wrong IMO

[Kulwinder Singh]

then what is best way to handle this case?

[gildor]

add try/catch or function that handles this on every request and react according to the case

[gildor]

some error should be visible to user, some shouldn’t

[louiscad]

Network can break at any time, in which case you'll get an IOException subclass thrown.

[gildor]

Also if you have connection it doesn’t mean you have access to internet

[gildor]

We usually just check type of exception:

fun Throwable.isNotConnected() = this is UnknownHostException || cause is UnknownHostException

fun Throwable.isTimeout() = this is SocketTimeoutException || cause is SocketTimeoutException

but it used only to handle it in UI, we never change interceptors or request logic

[gildor]

Also in general, every exception should be handled explicitly, depending on case, this isConnected doesn’t handle anything useful

[gildor]

I see your intent to simplify network logic, but for UI application, where you just cannot throw exception, you have to handle it, especially for Network, which is never stable enough, so if you will think about exception handling as about part of your UI logic, that you always should hanlde it, it makes it not so confusing, at least for me

[Kulwinder Singh]

Ok thanks, i understood your point and i have tried your method and to not repeat try/catch boilerplate i have created this high order function and it worked. let me know if it is ok ?

inline fun withNetworkCheck(call: () -> Unit) {
        try {
            call()
        } catch (e: Exception) {
            if (e.isNotConnected()) {
                toast("Not connected to internet")
            } else if (e.isTimeout()) {
                toast("Network connection timeout")
            }
        }

    }

    fun Throwable.isNotConnected() = this is UnknownHostException || cause is UnknownHostException
    fun Throwable.isTimeout() = this is SocketTimeoutException || cause is SocketTimeoutException

[Kulwinder Singh]

Used it like this

withNetworkCheck {
	val response = apiService.getItems().toNetworkResult()
        when (response) {
            is NetworkResult.Success -> onDataLoaded(response.data)
            is NetworkResult.Error -> toast(response.errorCode)
        }
}

[Kulwinder Singh]

please let me know if my i implementation is ok?

[ahulyk]

you can try something like this:

abstract class BaseUseCase<out T, in P> where T : Any {

    abstract suspend fun run(params: P): Result<Failure, T>

    operator fun invoke(
            scope: CoroutineScope,
            params: P,
            onResult: (Result<Failure, T>) -> Unit = {}
    ) {
        scope.launch {
            try {
                withContext(IO) { run(params) }
            } catch (e: Exception) {
                mapFailure(e)
            }
                    .run {
                        onResult(this)
                    }
        }
    }

    private fun mapFailure(e: Exception) =
            when (e) {
                is HttpException -> Failure.ServerError(e)
                is UnknownHostException, is SocketTimeoutException -> Failure.NetworkConnection(e)
                else -> Failure.FeatureFailure(e)
            }
                    .run {
                        Timber.w(e)
                        Result.Failure(this)
                    }


}

[Kulwinder Singh]

@ahulyk it looks new thing to me, can you please let me know how to use it

[Saran Akkaraviwat]

@jitrapon