Module with Main dispatcher is missing

Question

I'm trying to make a background call to my local database and update the UI with the results using coroutines. Here is my relevant code:

import kotlinx.coroutines.experimental.*
import kotlinx.coroutines.experimental.Dispatchers.IO
import kotlinx.coroutines.experimental.Dispatchers.Main
import kotlin.coroutines.experimental.CoroutineContext
import kotlin.coroutines.experimental.suspendCoroutine

class WarehousesViewModel(private val simRepository: SimRepository)
: BaseReactViewModel<WarehousesViewData>(), CoroutineScope {

private val job = Job()

override val coroutineContext: CoroutineContext
    get() = job + Main

override val initialViewData = WarehousesViewData(emptyList())

override fun onActiveView() {
    launch {
        val warehouses = async(IO) { loadWarehouses() }.await()
        updateViewData(viewData.value.copy(items = warehouses))
    }
}

private suspend fun loadWarehouses(): List<Warehouse> =
    suspendCoroutine {continuation ->
        simRepository.getWarehouses(object : SimDataSource.LoadWarehousesCallback {
            override fun onWarehousesLoaded(warehouses: List<Warehouse>) {
                Timber.d("Loaded warehouses")
                continuation.resume(warehouses)
            }

            override fun onDataNotAvailable() {
                Timber.d("No available data")
                continuation.resume(emptyList())
            }
        })
    }
}

My problem is that I get a runtime exception:

java.lang.IllegalStateException: Module with Main dispatcher is missing. Add dependency with required Main dispatcher, e.g. 'kotlinx-coroutines-android'

I already added these to my gradle:

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:0.30.1'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:0.26.0'

I'm a bit new to this, can someone help me?

Solution 1

Using just the kotlinx-coroutines-android version solves the problem.

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:0.30.1'

Solution 2

You may be missing some Proguard rules.

I had the same problem in release build and solved it by adding the following rules:

-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
-keepclassmembernames class kotlinx.** {
    volatile <fields>;
}

from https://github.com/Kotlin/kotlinx.coroutines/blob/master/ui/kotlinx-coroutines-android/example-app/app/proguard-rules.pro

Solution 3

Use both Core and Android dependency

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.6'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.6'

Solution 4

If you're facing this problem with coroutines version 1.3.8, add this rule in your proguard-rules.pro:

-keep class kotlinx.coroutines.android.AndroidDispatcherFactory {*;}

Solution 5

./gradlew assembleDebug --rerun-tasks

fixes it if the above answers don't work for you (because you already had the required dependencies and you are using R8 which does not need the proguard rules).

View more solutions

Comments

[Marko Topolnik]

kotlinx-coroutines-core is a transitive dependency of kotlinx-coroutines-android and the proper solution is to remove it.

[Lucas P.]

That was it for my case. I've added all of the keeps form the GitHub page you've provided. Thank you very much!

[Herbal7ea]

Good catch Marko! Just to clarify, Marko means remove kotlinx-coroutines-core, it's included in kotlinx-coroutines-android

[Alexei]

To be use in Kotlin 1.3 must use this implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.2.1'

[Pierry]

I've just change for my flavor and all right! thanks

[cren90]

The GitHub page linked is no longer available, 404's for me

[Ganesh Kanna]

It doesn't matter cren90 . I want to share as example. You can simply follow what I mentioned

[Khongor Bayarsaikhan]

as pointed below the accepted answer, using only the android is enough

[Alessandro Mautone]

I run into this as well and indeed seems like the AndroidDispatcherFactory was not deobfuscated properly. With this in the proguard rules it works

[DJ. Aduvanchik]

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.3' - is the most current if anyone wants to save a few seconds.

[Damn Vegetables]

@MarkoTopolnik I am confused. It is NOT an Android project, but a plain Kotlin console project (the one that prints "hello world" in the command prompt), and I have added org.jetbrains.kotlinx:kotlinx-coroutines-core-jvm:1.6.0 as another answer had suggested, and I encountered this runtime error when trying to use Dispatchers.Main. So, I should use kotlinx-coroutines-android even if it is not an Android project? kotlinx-coroutines-core-jvm has been deprecated and should no longer be used?

[Damn Vegetables]

@MarkoTopolnik I have tried switching to Android version, but it threw a new runtime exception: NoClassDefFoundError: android/os/Looper

[Marko Topolnik]

@DamnVegetables Indeed, don't try to use either kotlinx-coroutines-android or Dispatchers.Main outside of an Android application.