How to properly set up and close a `CoroutineScope...

# koin

[Mark]

How to properly set up and close a CoroutineScope for a Koin Scope?

[Saul Wiggin]

Close the Koin scope val scope = getKoin().createScope<A>() scope.close() Close the Coroutine scope val coroutineScope = CoroutineScope(Job() + dispatchers.Main) coroutineScope.cancel()

[Mark]

Thanks Saul. Would it be better to use a SupervisorJob() and Dispatchers.Main.immediate since that it what ViewModel.viewModelScope uses? Maybe also use by lazy since there is no point creating the scope unnecessarily.

[Mark]

Here’s what I have so far regarding Android’s Navigation Graphs.

scope(navQualifier(R.id.nav_item)) {
    scoped { (coroutineScope: CoroutineScope) ->
        MyModel(someArg = get(), coroutineScope)
    }
}

// fragment
val viewModel by navGraphInstances<MyModel>(R.id.nav_item)

// common code
inline fun <reified T : Any> Fragment.navGraphInstances(
    @IdRes navGraphId: Int
): Lazy<T> = lazy {
    val holder by navGraphViewModels<NavGraphScopeHolder>(navGraphId) {
        object : ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T =
                NavGraphScopeHolder(navGraphId) as T
        }
    }
    holder.scope.get { parametersOf(holder.viewModelScope) }
}

class NavGraphScopeHolder(@IdRes navGraphId: Int) : ViewModel() {

    val scope = GlobalContext.get().getOrCreateScope(
        navScopeId(navGraphId),
        navQualifier(navGraphId)
    )

    override fun onCleared() {
        scope.close()
    }
}

fun navQualifier(navGraphId: Int) = named("NavQualifier (NavGraphId@$navGraphId)")

fun navScopeId(navGraphId: Int): ScopeID = "NavScopeId (NavGraphId@$navGraphId)"

[Saul Wiggin]

I think for this case SupervisorJob + Dispatchers.Main.intermediate would be the correct configuration for this situation. Is it possible to use lateinit var instead of initializing by lazy?

[Mark]

I figured anyway, I’m passing the coroutineScope to the model, so my concern doesn’t make sense!

[Saul Wiggin]

Yeah. That’s true.

[Mark]

Also realised, in the above example, there is no need to cancel the viewModelScope because that is done for us since we are making use of Android’s ViewModel