Develop Reference

Compose WorkManager not getting triggered

I have an app that uses a Worker to update its services via the internet.
However, the worker is not getting triggered.
Worker.kt:
class MyWorker(
private val container: AppContainer,
ctx: Context,
params: WorkerParameters
) : CoroutineWorker(ctx, params) {
override suspend fun doWork(): Result {
return withContext(Dispatchers.IO) {
return#withContext try {
val response = container.onlineRepository.getData()
// Load the data
container.offlineRepository.load(
data = response.data
)
Result.success()
} catch (throwable: Throwable) {
Log.e(
TAG, throwable.message, throwable
)
Result.failure()
}
}
}
}
DataActivity.kt:
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val worker = OneTimeWorkRequestBuilder<MyWorker>().build()
WorkManager.getInstance(this).enqueue(worker)
setContent {
DataApp()
}
}
When i check the logs, nothing is being logged because it is not entering the doWork()
Can someone please help ?

In yourMyWorker class constructor, you are requiring thecontainer: AppContainer argument which is not supplied on instantiation. It's better to use WorkerParameters to achieve this.
You could use this:
// Passing params
Data.Builder data = new Data.Builder();
data.putString("my_key", my_string);
val worker = OneTimeWorkRequestBuilder<MyWorker>()
.setInputData(data.build())
.build()
WorkManager.getInstance(this).enqueue(worker)
However, WorkManager's Data class only accepts some specific types as values as explained in the reference documentation.
On top of that, there's a size limit of about 10 KB, specified by the constant MAX_DATA_BYTES.
If the data is not too big, you may want to serialize it to a String and use that as inputData in your WorkRequest.

Best practise for replacing current coroutine call in viewmodels

I have the following:
interface CartRepository {
fun getCart(): Flow<CartState>
}
interface ProductRepository {
fun getProductByEan(ean: String): Flow<Either<ServerError, Product?>>
}
class ScanViewModel(
private val productRepository: ProductRepository,
private val cartRepository: CartRepository
) :
BaseViewModel<ScanUiState>(Initial) {
fun fetchProduct(ean: String) = viewModelScope.launch {
setState(Loading)
productRepository
.getProductByEan(ean)
.combine(cartRepository.getCart(), combineToGridItem())
.collect { result ->
when (result) {
is Either.Left -> {
sendEvent(Error(R.string.error_barcode_product_not_found, null))
setState(Initial)
}
is Either.Right -> {
setState(ProductUpdated(result.right))
}
}
}
}
}
When a user scans a barcode fetchProduct is being called. Every time a new coroutine is being set up. And after a while, there are many running in the background and the combine is triggered when the cart state is updated on all of them, which can cause errors.
I want to cancel all old coroutines and only have the latest call running and update on cart change.
I know I can do the following by saving the job and canceling it before starting a new one. But is this really the way to go? Seems like I'm missing something.
var searchJob: Job? = null
private fun processImage(frame: Frame) {
barcodeScanner.process(frame.toInputImage(this))
.addOnSuccessListener { barcodes ->
barcodes.firstOrNull()?.rawValue?.let { ean ->
searchJob?.cancel()
searchJob = viewModel.fetchProduct(ean)
}
}
.addOnFailureListener {
Timber.e(it)
messageMaker.showError(
binding.root,
getString(R.string.unknown_error)
)
}
}
I could also have a MutableSharedFlow in my ViewModel to make sure the UI only react to the last product the user has been fetching:
private val productFlow = MutableSharedFlow<Either<ServerError, Product?>>(replay = 1)
init {
viewModelScope.launch {
productFlow.combine(
mycroftRepository.getCart(),
combineToGridItem()
).collect { result ->
when (result) {
is Either.Right -> {
setState(ProductUpdated(result.right))
}
else -> {
sendEvent(Error(R.string.error_barcode_product_not_found, null))
setState(Initial)
}
}
}
}
}
fun fetchProduct(ean: String) = viewModelScope.launch {
setState(Loading)
repository.getProductByEan(ean).collect { result ->
productFlow.emit(result)
}
}
What's considered best practice handling this scenario?

I can't think of a simpler pattern for cancelling any previous Job when starting a new one.
If you're concerned about losing your stored job reference on screen rotation (you probably won't since Fragment instances are typically reused on rotation), you can move Job storage and cancellation into the ViewModel:
private var fetchProductJob: Job? = null
fun fetchProduct(ean: String) {
fetchProductJob?.cancel()
fetchProductJob = viewModelScope.launch {
//...
}
}
If you're repeatedly using this pattern, you could create a helper class like this. Not sure if there's a better way.
class SingleJobPipe(val scope: CoroutineScope) {
private var job: Job? = null
fun launch(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
): Job = synchronized(this) {
job?.cancel()
scope.launch(context, start, block).also { job = it }
}
}
// ...
private val fetchProductPipe = SingleJobPipe(viewModelScope)
fun fetchProduct(ean: String) = fetchProductPipe.launch {
//...
}

How to properly set Observable in the Activity to Pass data from API call in view model into Activity + Data Class for the list. Android Compose

I think my observable is set incorrectly here. I am using Retrofit2 + Moshi as the deserializer, and the API call from Retrofit is working.
But once I make the API call, I am trying to set up the Observable in my Activity and then use the API call data from the data class.
Here is my view model code:
class DealsViewModel(val repository: MainRepository) : ViewModel() {
val movieList = MutableLiveData<List<DealItems>>()
var job: Job? = null
val loading = MutableLiveData<Boolean>()
val errorMessage = MutableLiveData<String>()
val exceptionHandler = CoroutineExceptionHandler { _, throwable ->
onError("Exception handled: ${throwable.localizedMessage}")
}
fun getMovies() {
viewModelScope.launch{
// View Model Scope gives the Coroutine that will be canceled when the ViewModel is cleared.
job = CoroutineScope(Dispatchers.IO + exceptionHandler).launch {
val items = repository.getProduct()
withContext(Dispatchers.Main) {
if (items.isNullOrEmpty()) {
loading.value = false
// put error message in here later
} else {
dealList.postValue(items)
return#withContext
}
}
}
}
}
private fun onError(message: String) {
errorMessage.value = message
loading.value = false
}
override fun onCleared() {
super.onCleared()
job?.cancel()
}
}
And here is my MainActivity code.
I am using JetpackCompose in my activity, LiveData for the API response container. In my main repository is where I am validating a successful API response and then the coroutines for the call are inside of the view model.
My API call is successful, but I am not sure where to call the ViewModel.GetMovies() inside of the activity and I am not sure if the observables are set properly and/or where to pass the API's livedata into my composable function.
Thanks for any help you can provide. I am new to android and trying to use Coroutines for the first time.
class MainActivity: ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val retrofitService = RetrofitService.getInstance()
val viewModel = ViewModelProvider(this,
MyViewModelFactory(MainRepository(retrofitService = retrofitService))).get(DealsViewModel::class.java)
// viewModel.getProducts()
setContent {
myApp {
MyScreenContent()
}
viewModel.movieList.observe(
this, { it ->
if( it != null) {
it.forEach {
var movieLocation = it.movieLocation
val description = it.description
val id = it.id
val title = it.title
val regularPrice = it.regularPrice
}
}
})
return#setContent
}
viewModel.errorMessage.observe(this, {
Toast.makeText(this, it, Toast.LENGTH_SHORT).show()
})
viewModel.loading.observe(
this,
Observer {
if (it) {
}
})
}
}

I assume that it always depends when should you call especially in the activity we have many lifecycles; however, the best way is to use the .also on the livedata/stateflow lazy creation so that you do guarantee as long as the view model is alive, the getMovies is called only one time, and also guarantee the service itself is not called unless someone is listening to it.
You may check the full documentation in this link
Here is a code example
class MyViewModel : ViewModel() {
private val users: MutableLiveData<List<User>> by lazy {
MutableLiveData<List<User>>().also {
loadUsers()
}
}
fun getUsers(): LiveData<List<User>> {
return users
}
private fun loadUsers() {
// Do an asynchronous operation to fetch users.
}
}
When using this code, you do not have to call getMovies at all in the activity, you just listen to the observer.

How to get result using registerForActivityResult from within ktor's Routing call running in a non-activity class?

How to get result from another activity (registerForActivity) from with in ktor's Routing API call (eg. /POST) running in a non-activity class?
Background: For an Android app, I run ktor server engine 'netty' in a non-activity class HttpServer.kt. I need to call another app's activity from with in ktor's Routing' POST handler, so I pass 'appCompatActivity' from MainActivity.kt. That's done, just because, I assume, registerForActivityResult() has dependency on UI/life cycle class.
Problem arises when running this as below, as registerForActivityResult() requires to be run earlier (like onCreate() ?), and I don't have such a class in this non-activity class. Moreover, the callback to run when ActivityResult is returned needs to call ktor ApplicationCall's respond which is also a suspend function.
class HttpServer(
private val applicationContext: AppCompatActivity
) {
private val logger = LoggerFactory.getLogger(HttpServer::class.java.simpleName)
private val server = createServer()
private fun ApplicationCall.startSaleActivityForResult() { // <====== *
val activityLauncherCustom =
applicationContext.registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult ->
if (result.resultCode == Activity.RESULT_OK || result.resultCode == Activity.RESULT_CANCELED) {
val transactionResultReturned = result.data
// Handle the returned result properly using transactionResultReturned
GlobalScope.launch {
respond(status = HttpStatusCode.OK, TransactionResponse())
}
}
}
val intent = Intent()
// Ignoring statements to create proper action/data intent
activityLauncherCustom.launch(intent) // <====== *
}
fun start() = server.start()
fun stop() = server.stop(0, 0)
private fun createServer(): NettyApplicationEngine {
return GlobalScope.embeddedServer(Netty) {
install(CallLogging)
install(ContentNegotiation) {
gson {
setPrettyPrinting()
}
}
routing {
route("/") {
post {
call.startSaleActivityForResult() // <====== *
}
}
}
}
}
private fun <TEngine : ApplicationEngine, TConfiguration : ApplicationEngine.Configuration>
CoroutineScope.embeddedServer(
factory: ApplicationEngineFactory<TEngine, TConfiguration>,
module: Application.() -> Unit
): TEngine {
val environment = applicationEngineEnvironment {
this.parentCoroutineContext = coroutineContext + parentCoroutineContext
this.log = logger
this.module(module)
connector {
this.port = 8081
}
}
return embeddedServer(factory, environment)
}
}
Above is what I tried, but gives below error. And I don't have onCreate on this non-activity class.
java.lang.IllegalStateException: LifecycleOwner com.youtap.upti.MainActivity#38dcf06 is attempting to register while current state is RESUMED. LifecycleOwners must call register before they are STARTED.
Any suggestions to resolve this problem would be grateful.
Below same above snippet as a screenshot to display helper text on declaration/param types from Android Studio:
And I invoke this server class from onCreate() of MainActivity:

To solve your problem and to hide the complexity you can create an intermediate class for launching activity and waiting for a result to come:
import kotlinx.coroutines.channels.Channel
class Repository(private val activity: MainActivity) {
private val channel = Channel<Int>(1)
suspend fun get(input: String): Int {
activity.activityLauncher.launch(input)
return channel.receive()
}
suspend fun callback(result: Int) {
channel.send(result)
}
}
You can store a reference to a repository and an activity launcher in the MainActivity class:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
CoroutineScope(Dispatchers.IO).launch {
HttpServer(this#MainActivity).also { it.start() }
}
}
val activityLauncher = registerForActivityResult(MySecondActivityContract()) { result ->
GlobalScope.launch {
repository.callback(result!!)
}
}
val repository = Repository(this)
}
My second activity and a contract looks like the following:
class ChildActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_child)
val result = Intent()
result.putExtra("name", 6666)
result.data = Uri.parse("http://mydata")
setResult(Activity.RESULT_OK, result)
finish()
}
}
class MySecondActivityContract : ActivityResultContract<String, Int?>() {
override fun createIntent(context: Context, input: String?): Intent {
return Intent(context, ChildActivity::class.java)
.putExtra("my_input_key", input)
}
override fun parseResult(resultCode: Int, intent: Intent?): Int? = when {
resultCode != Activity.RESULT_OK -> null
else -> intent?.getIntExtra("name", 42)
}
override fun getSynchronousResult(context: Context, input: String?): SynchronousResult<Int?>? {
return if (input.isNullOrEmpty()) SynchronousResult(42) else null
}
}
The most simplest part is routing handler:
routing {
route("/") {
post {
val result = (applicationContext as MainActivity).repository.get("input")
call.respondText { result.toString() }
}
}
}
This solution works but only one request is processed at the same time and it's not robust because Activity may be destroyed before HTTP server or repository objects.

How to return value from async coroutine scope such as ViewModelScope to your UI?

I'm trying to retrieve a single entry from the Database and successfully getting the value back in my View Model with the help of viewModelScope, but I want this value to be returned back to the calling function which resides in the fragment so it can be displayed on a TextView. I tried to return the value the conventional way but it didn't work. So, How Can I return this value from viewModelScope.launch to the calling function?
View Model
fun findbyID(id: Int) {
viewModelScope.launch {
val returnedrepo = repo.delete(id)
Log.e(TAG,returnedrepo.toString())
// how to return value from here to Fragment
}
}
Repository
suspend fun findbyID(id : Int):userentity{
val returneddao = Dao.findbyID(id)
Log.e(TAG,returneddao.toString())
return returneddao
}

LiveData can be used to get value from ViewModel to Fragment.
Make the function findbyID return LiveData and observe it in the fragment.
Function in ViewModel
fun findbyID(id: Int): LiveData</*your data type*/> {
val result = MutableLiveData</*your data type*/>()
viewModelScope.launch {
val returnedrepo = repo.delete(id)
result.postValue(returnedrepo)
}
return result.
}
Observer in Fragment
findbyId.observer(viewLifeCycleOwner, Observer { returnedrepo ->
/* logic to set the textview */
})

Thank you Nataraj KR for your Help!
Following is the code that worked for me.
View Model
class ViewModel(application: Application):AndroidViewModel(application) {
val TAG = "ViewModel"
val repo: theRepository
val alldata:LiveData<List<userentity>>
val returnedVal = MutableLiveData<userentity>()
init {
val getDao = UserRoomDatabase.getDatabase(application).userDao()
repo = theRepository(getDao)
alldata = repo.allUsers
}
fun findbyID(id: Int){
viewModelScope.launch {
returnedVal.value = repo.findbyID(id)
}
}
}
Fragment
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
val usermodel = ViewModelProvider(this).get(ViewModel::class.java)
usermodel.alldata.observe(this, Observer {
Log.e(TAG,usermodel.alldata.value.toString())
})
usermodel.returnedVal.observe(this, Observer {
tv1.text = usermodel.returnedVal.value.toString()
})
allData.setOnClickListener {
tv1.text = usermodel.alldata.value.toString()
}
findByID.setOnClickListener {
usermodel.findbyID(et2.text.toString().toInt())
}
}

Another way without using LiveData would be like this,
Similar to viewModelScope there is also a lifecycleScope available with lifecycle-aware components, which can be used from the UI layer. Following is the example,
Fragment
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
findByID.setOnClickListener {
lifecycleScope.launch{
val res = usermodel.findbyID(et2.text.toString().toInt())
// use returned value to do anything.
}
}
}
ViewModel
//1st option
// make the function suspendable itself.use aync instead of launch and then
// use await to collect the returned value.
suspend fun findbyID(id: Int): userEntity {
val job = viewModelScope.async {
val returnedrepo = repo.delete(id)
Log.e(TAG,returnedrepo.toString())
return#async returnedrepo
}
return job.await()
}
//2nd option
// make the function suspendable itself. but switch the execution on IO
// thread.(since you are making a DB call)
suspend fun findbyID(id: Int): userEntity {
return withContext(Dispatchers.IO){
val returnedrepo = repo.delete(id)
Log.e(TAG,returnedrepo.toString())
return#withContext returnedrepo
}
}
Since LiveData is specific to Android Environment, Using Kotlin Flow becomes a better option in some places, which offers similar functionality.