kotlin-coroutines

I have a use case where I need to connect and disconnect from a class that acts as a service. Actions can be performed on the service only when the service is connected. Clients are notified when the service connects or disconnects by a callback: class Service { constructor(callback: ConnectionCallback) { ... } fun connect() { // Call callback.onConnected() some time after this method returns. } fun disconnect() { // Call callback.onConnectionSuspended() some time after this method returns. } fun isConnected(): Boolean { ... } fun performAction(actionName: String, callback: ActionCallback) { /

I can't seem to get my error-handling done in coroutines. I've been reading lots of articles and the exception handling documentation but I can't seem to get it working. Here's my setup: My ViewModel launches the coroutine with it's scope class MyViewModel(private var myUseCase: MyUseCase) : ViewModel() { private val viewModelJob = Job() private val uiScope = CoroutineScope(Dispatchers.Main + viewModelJob) fun doSomething() { uiScope.launch { try { myUseCase() } catch (exception: Exception) { // Do error handling here } } } } My UseCase just handles a few logic and in this case a validator of

I want to test my database layer and I have caught myself in a catch-22 type of a situation. The test case consists of two things: Save some entities Load the entities and assert the database mapping works as expected The problem, in short, is that: Insert is a suspend method, which means it needs to be run in runBlocking{} Query returns a LiveData of the result, which is also asynchronous. Therefore it needs to be observed. There's this SO question that explains how to do that. In order to observe the LiveData according to the above link, however, I must use the InstantTaskExecutorRule .

I'm trying to use Coroutines with a Room database in an Android project. I've found almost no documentation online, and I'm wondering if it is possible to return Deferred<> types in those methods. Something like this: @Dao interface MyObjectDAO { @Query("SELECT * FROM myObject WHERE id_myObject = :idMyObject") suspend fun readMyObjectAsync(idMyObject: Int): Deferred<MyObject> } I've tried this and I get Not sure how to convert a Cursor to this method's return type at compile time. My dependencies are: kapt 'androidx.room:room-compiler:2.1.0-alpha04' implementation 'androidx.room:room-runtime:2

This code: fun main() { runBlocking { try { val deferred = async { throw Exception() } deferred.await() } catch (e: Exception) { println("Caught $e") } } println("Completed") } results in this output: Caught java.lang.Exception Exception in thread "main" java.lang.Exception at org.mtopol.TestKt$main$1$deferred$1.invokeSuspend(test.kt:11) ... This behavior doesn't make sense to me. The exception was caught and handled, and still it escapes to the top-level as an unhandled exception. Is this behavior documented and expected? It violates all my intuitions on how exception handling is supposed to

I am learning Kotlin coroutines. I've read that runBlocking is the way to bridge synchronous and asynchronous code. But what is the performance gain if the runBlocking stops the UI thread? For example, I need to query a database in Android: val result: Int get() = runBlocking { queryDatabase().await() } private fun queryDatabase(): Deferred<Int> { return async { var cursor: Cursor? = null var queryResult: Int = 0 val sqlQuery = "SELECT COUNT(ID) FROM TABLE..." try { cursor = getHelper().readableDatabase.query(sqlQuery) cursor?.moveToFirst() queryResult = cursor?.getInt(0) ?: 0 } catch (e: