Hey there, i have already asked this in the <#CRJC...

# android

[althaf]

Hey there, i have already asked this in the #flow its been 3 days without answer, so i'm posting it here

I"m not able to use coroutine Context, in the flowOn(....), app is crashing with

java.lang.IllegalArgumentException: Flow context cannot contain job in it. Had [SupervisorJobImpl{Active}@7b4ca1f, <http://Dispatchers.IO|Dispatchers.IO>]

interface UseCaseScope : CoroutineScope {
    override val coroutineContext: CoroutineContext
        get() = SupervisorJob() + <http://Dispatchers.IO|Dispatchers.IO>
}

FlowUsecase : UseCaseScope {
 <snip>
}

The intention here is to cancel the coroutine context when we business logic need to cancel it. So that i can call coroutineContext.cancel()

class LoginUseCase(private val authRepository: AuthRepository) : FlowUseCase<LoginRequest, Boolean>() {

    override fun execute(parameter: LoginRequest): Flow<Result<Boolean>> =
        flow {
            authRepository.login(parameter.username, parameter.password).collect { response ->
                this.defaultResultHandler(onSuccess = {
                    emit(Result.success(true))
                }, response)
            }
        }.flowOn(coroutineContext)

    override fun cancel() {
        coroutineContext.cancel()
    }
}

^^^ will cause app the crash

[Ciaran Sloan]

the error states Flow context cannot contain job in it. Therefor you should not be passing a job to the .flowOn operator. Instead pass the dispatcher

[Ciaran Sloan]

if you want to cancel the flow collection, you should cancel the job which consumes the execute flow

[Ciaran Sloan]

so in some class that consumes the LoginUseCase you would have:

class MyClass(
    private val loginUseCase: LoginUseCase
) {
	fun doWork() {
		scope.launch {
		    loginUseCase.execute(...)
		        .collect()
		}
	}

	fun cleanup() {
	    scope.cancel() //
	}
}

[althaf]

@Ciaran Sloan thank you