lukaslechnerdev/kotlin-coroutines-and-flow-usecases-on-android

🎓 Learning Kotlin Coroutines and Flows for Android by example. 🚀 Sample implementations for real-world Android use cases. 🛠 Unit tests included!

kotlin-coroutines-and-flow-usecases-on-android's Issues

Usecase for StateFlow and SharedFlow

Adding usecase for StateFlow and SharedFlow would be helpful.

Main or IO thread

According to this code your network request will be made in MainThread. Isn't it?

`class PerformSingleNetworkRequestViewModel(
private val mockApi: MockApi = mockApi()
) : BaseViewModel() {

fun performSingleNetworkRequest() {
    uiState.value = UiState.Loading
    viewModelScope.launch {
        try {
            val recentAndroidVersions = mockApi.getRecentAndroidVersions()
            uiState.value = UiState.Success(recentAndroidVersions)
        } catch (exception: Exception) {
            Timber.e(exception)
            uiState.value = UiState.Error("Network Request failed!")
        }
    }
}}`

Maybe need to change it a little bit to launch(Dispatchers.IO) {... and uiState.postValue(...)

Perform several network requests concurrently

coroutineScope {
                    val oreoFeaturesDeferred = async { mockApi.getAndroidVersionFeatures(27) }
                    val pieFeaturesDeferred = async { mockApi.getAndroidVersionFeatures(28) }
                    val android10FeaturesDeferred = async { mockApi.getAndroidVersionFeatures(29) }

                    val oreoFeatures = oreoFeaturesDeferred.await()
                    val pieFeatures = pieFeaturesDeferred.await()
                    val android10Features = android10FeaturesDeferred.await()

                    val versionFeatures = listOf(oreoFeatures, pieFeatures, android10Features)

                    // other alternative: (but slightly different behavior when a deferred fails, see docs)
                    // val versionFeatures = awaitAll(oreoFeaturesDeferred, pieFeaturesDeferred, android10FeaturesDeferred)

                    uiState.value = UiState.Success(versionFeatures)
                }

i have some question about this code, deferred's await() function will suspend this coroutines, so this demo code can't performed in parallel

Typo in name of test function

https://github.com/LukasLechnerDev/Kotlin-Coroutine-Use-Cases-on-Android/blob/master/app/src/test/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase4/VariableAmountOfNetworkRequestsViewModelTest.kt
Line 108.
Name of the function should be:
performNetworkRequestsConcurrently() should return Success UiState on successful network requests after 2000ms
instead of:
performNetworkRequestsConcurrently() should return Error UiState on successful network requests after 2000ms

This can be done by synchronously with the help of withContext?

https://github.com/LukasLechnerDev/Kotlin-Coroutine-Use-Cases-on-Android/blob/fd939486e24ddad1815c2fa0330c0109c4752e76/app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase14/AndroidVersionRepository.kt#L21

Corounties

usecase4/VariableAmountOfNetworkRequestsViewModel#performNetworkRequestsConcurrently crashes on exception

Hi, Lukas!

I think there's a problem with the solution for

usecase4/VariableAmountOfNetworkRequestsViewModel#performNetworkRequestsConcurrently.

It crashes when I configure MockApi to return a 500 on the call to http://localhost/android-version-features/28.

Reading this about exceptions, it seems like try-catch will not catch the exception because async is not the direct child of the scope - launch is. So async will propagate the exception up to its parent (launch) and launch will throw the exception.

What do you think?

- Julian

Add info about Workmanager gotcha

Here's something that caught me out while using WorkManager with coroutines that you might want to add: Do not call a suspend function in the catch block (when you are trying to set the action as failed in the database etc). It will not be called when the work is cancelled due to system constraints. In that case WorkManager will throw JobCancellationException which means suspend functions will re-throw immediately. If you really want the suspend function to run, you must use NonCancellable context.
See: https://kotlinlang.org/docs/reference/coroutines/cancellation-and-timeouts.html#run-non-cancellable-block

For case 13(Exception handling),the last sub-case is missing.

Propagating state

Please how best can propagate state(like status) from the repository down to viewmodel using coroutine(no livedata usage in repository)?.
I read a medium article about livedata usage in any other layers aside presentation being inappropriate