This version of the app is called todo-mvp-kotlin-coroutines and is based on todo-mvp-kotlin. The sample aims to:

• Replace all asynchronous operations with coroutines, which simplify asynchronous programming by providing possibility to write code in direct style (sequentially).

Before exploring this sample, you should familiarize yourself with the following topics:

• The project README
• The todo-mvp sample
• The todo-mvp-kotlin sample
• Kotlin coroutine documentation

• kotlin stdlib
• kotlin-android plugin
• kotlinx-coroutines-core
• kotlinx-coroutines-android

All functions in TasksDataSource replaces with suspend functions.

interface TasksDataSource {
    suspend fun getTasks(): Result<List<Task>>
    suspend fun getTask(taskId: String): Result<Task>
    suspend fun saveTask(task: Task)
    suspend fun completeTask(task: Task)
    suspend fun completeTask(taskId: String)
    suspend fun activateTask(task: Task)
    suspend fun activateTask(taskId: String)
    suspend fun clearCompletedTasks()
    suspend fun refreshTasks()
    suspend fun deleteAllTasks()
    suspend fun deleteTask(taskId: String)
}

In todo-mvp-kotlin sample functions getTasks and getTask had callbacks with onTasksLoaded and onDataNotAvailable functions. In todo-mvp-kotlin-coroutines sample this functions now return Result which can be ether a Success or Error.

sealed class Result<out T : Any> {
    class Success<out T : Any>(val data: T) : Result<T>()
    class Error(val exception: Throwable) : Result<Nothing>()
}

To launch coroutines you need to specify a CoroutineContext. In tests all coroutines are launched via runBlocking or with EmptyCoroutineContext.

@Test
fun loadStatisticsWhenTasksAreUnavailable_CallErrorToDisplay() = runBlocking {
    // Tasks data isn't available
    setTasksNotAvailable(tasksRepository)

    // When statistics are loaded
    statisticsPresenter.start()

    // Then an error message is shown
    verify(statisticsView).showLoadingStatisticsError()
}

Files were converted mostly 1:1 from TODO-MVP's Java code.

-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
Kotlin                          54            944           1604           3107 (3060 in MVP-kotlin)
XML                             34             95            338            816
-------------------------------------------------------------------------------
SUM:                            89           1039           1942           3923
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