Blueprint Coroutines Demo¶

This is simple note taking app for demonstrating how to use Blueprint in a codebase that uses Kotlin Coroutines and Flow.

Interactors¶

The demo app follows Clean Architecture. The Use Cases (also known as Interactors) define and encapsulate business rules specific to the application.

The blueprint-interactor-coroutines artifact provides 2 base classes for building Interactors:

SuspendingInteractor for single-shot tasks
FlowInteractor for cold streams

An example implementation of SuspendingInteractor in the app:

class CoroutinesCreateNote(
    private val noteRepository: CoroutinesNoteRepository,
    coroutineDispatcherProvider: CoroutineDispatcherProvider
) : SuspendingInteractor<CoroutinesCreateNote.Params, Unit>() {
    override val dispatcher: CoroutineDispatcher = coroutineDispatcherProvider.io

    override suspend fun doWork(params: Params) {
        noteRepository.addNote(params.note)
    }

    class Params(internal val note: Note) : InteractorParams
}

Call-side:

viewModelScope.launch {
    val time = System.currentTimeMillis()
    val newNote = Note(
        content = content,
        timeCreated = time,
        timeLastUpdated = time
    )
    createNote.execute(CoroutinesCreateNote.Params(newNote))
}

An example implementation of FlowInteractor in the app:

class CoroutinesStreamAllNotes(
    private val noteRepository: CoroutinesNoteRepository,
    coroutineDispatcherProvider: CoroutineDispatcherProvider
) : FlowInteractor<CoroutinesStreamAllNotes.Params, List<Note>>() {
    override val dispatcher: CoroutineDispatcher = coroutineDispatcherProvider.io

    override fun createFlow(params: Params): Flow<List<Note>> {
        return noteRepository.streamAllNotes()
            .map { notes ->
                if (params.sortedBy === SortedBy.TIME_CREATED) {
                    notes.sortedByDescending { it.timeCreated }
                } else {
                    notes.sortedByDescending { it.timeLastUpdated }
                }
            }
    }

    class Params(internal val sortedBy: SortedBy) : InteractorParams

    enum class SortedBy {
        TIME_CREATED,
        TIME_LAST_UPDATED
    }
}

Call-side:

streamAllNotes.buildFlow(CoroutinesStreamAllNotes.Params(CoroutinesStreamAllNotes.SortedBy.TIME_LAST_UPDATED))
    .map { State.Idle(it) }
    .onStart<State> {
        emit(State.LoadingNotes)
    }
    .onEach {
        // propagate value of each Flow emission to LiveData<State>
        notesLiveData.value = it
    }
    .catch {
        Timber.e(it)
    }
    // launch the collection of the Flow in the [viewModelScope] from "androidx.lifecycle:lifecycle-viewmodel-ktx"
    .launchIn(viewModelScope)

Threading¶

The CoroutineDispatcherProvider from the examples above is responsible encapsulating the threading behavior with a wrapper API.

This class from the blueprint-async-coroutines artifact has 3 properties, representing the common groups of threading use cases in an app:

io: CoroutineDispatcher - Dispatcher for IO-bound work
computation: CoroutineDispatcher - Dispatcher for computational work
ui: CoroutineDispatcher - Dispatcher for UI work

An instance of this can be injected to classes which are concerned about executing code on different threads, but they don’t and shouldn’t need to know about the underlying implementation. A single-threaded version for example can be injected for testing.

Practically you’ll likely only have 1 instance of CoroutineDispatcherProvider in the production environment and use DI to inject it into anywhere in the codebase where certain threading behavior is required:

CoroutineDispatcherProvider(
    io = Dispatchers.IO,
    computation = Dispatchers.Default,
    ui = Dispatchers.Main.immediate
)

In unit tests you can easily swap out the implementation to make sure code is executed in a single thread:

CoroutineDispatcherProvider(
    io = testCoroutineDispatcher,
    computation = testCoroutineDispatcher,
    ui = testCoroutineDispatcher
)

where testCoroutineDispatcher is an instance of TestCoroutineDispatcher from the org.jetbrains.kotlinx:kotlinx-coroutines-test library.

For a full example please look at the unit tests for Interactors e.g. CoroutinesStreamAllNotesTest.kt.

UI Widget and Extensions¶

The demo app uses various Kotlin extensions and widget from the blueprint-ui artifact:

For launching a new Activity from an Activity:

launchActivity<CoroutinesEnterNoteActivity> {
    putExtra(EXTRA_ENTER_NOTE_PARAMS, EnterNoteParams.CreateNew)
}

UI Testing¶

The UI testing framework and Testing Robot DSL from the blueprint-testing-robot provide the building blocks for authoring structured, readable, and framework-agnostic UI tests.

An example of a test case:

@Test
fun openNotesListScreenWithExistingNotes_notesDisplayed() {
    notesListScreen {
        given {
            noteCache.addNotes(testNotes)
        }
        perform {
            launchActivityScenario<CoroutinesNotesListActivity>()
        }
        check {
            createNoteButtonDisplayed()
            notesDisplayed(testNotes)
        }
    }
}

This DSL is powered by a custom Screen Robot implementation. Examples can be found in demo-testing-common.

Building¶

To compile the app:

./gradlew demo-coroutines:assemble

To run unit tests, lint and detekt:

./gradlew demo-coroutines:check

To run UI (on-device) tests:

./gradlew demo-coroutines:connectedCheck