This is the eventbus implementation using Broadcast channel. (RxJava2 not allowed :( )
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.channels.*
import kotlin.coroutines.CoroutineContext
class EventBus(override val coroutineContext: CoroutineContext
= Dispatchers.Default) :CoroutineScope {
#ExperimentalCoroutinesApi
private val channel = BroadcastChannel<Any>(1)
#ExperimentalCoroutinesApi
suspend fun send(event: Any) {
channel.send(event)
}
#ExperimentalCoroutinesApi
fun subscribe(): ReceiveChannel<Any> =
channel.openSubscription()
#ExperimentalCoroutinesApi
inline fun <reified T> subscribeToEvent() =
subscribe().let {
produce<T>(coroutineContext) {
for (t in it){
if(t is T)
send(t as T)
}
}
}
}
And here is my testing code.
#Test
fun testEventBus(){
val bus = EventBus()
var i = 1;
var isFinish = false
CoroutineScope(Dispatchers.IO).launch{
println("launching_subsc")
bus.subscribe().consumeEach {
println("received $it")
assert(it == i++)
isFinish = (it == 5)
}
withContext(bus.coroutineContext){
}
}
bus.launch {
delay(500)
for (j in 1..5) {
println("sending $j")
bus.send(j)
sleep(500)
}
}
while (!isFinish)
sleep(50)
}
This test works good, but I want to remove the delay(500) and yet expect the test to work.
If I remove the delay(500) now, the output is
launching_subsc
sending 1
sending 2
received 2
...
or
sending 1
launching_subsc
sending 2
received 2
...
My actual need is that in actual project scenario I want the data to be published after the subscription, again, if there is no subscriber, the events need to be dropped.
So if there is a subscription call before publishing call(irrespective of Dispatchers) the subscriber must receive all the events.
I have tried using the same scope/dispatcher, nothing is working.
Related
I'm trying to insert separators to my list using the paging 3 compose library however, insertSeparators doesn't seem to indicate when we are at the beginning or end. My expectations are that before will be null at the beginning while after will be null at the end of the list. But it's never null thus hard to know when we are at the beginning or end. Here is the code:
private val filterPreferences =
MutableStateFlow(HomePreferences.FilterPreferences())
val games: Flow<PagingData<GameModel>> = filterPreferences.flatMapLatest {
useCase.execute(it)
}.map { pagingData ->
pagingData.map { GameModel.GameItem(it) }
}.map {
it.insertSeparators {before,after->
if (after == null) {
return#insertSeparators null
}
if (before == null) {
Log.i(TAG, "before is null: ") // never reach here
return#insertSeparators GameModel.SeparatorItem("title")
}
if(condition) {
GameModel.SeparatorItem("title")
}
else null
}
}
.cachedIn(viewModelScope)
GamesUseCase
class GamesUseCase #Inject constructor(
private val executionThread: PostExecutionThread,
private val repo: GamesRepo,
) : FlowUseCase<HomePreferences, PagingData<Game>>() {
override val dispatcher: CoroutineDispatcher
get() = executionThread.io
override fun execute(params: HomePreferences?): Flow<PagingData<Game>> {
val preferences = params as HomePreferences.FilterPreferences
preferences.apply {
return repo.fetchGames(query,
parentPlatforms,
platforms,
stores,
developers,
genres,
tags)
}
}
}
FlowUseCase
abstract class FlowUseCase<in Params, out T>() {
abstract val dispatcher: CoroutineDispatcher
abstract fun execute(params: Params? = null): Flow<T>
operator fun invoke(params: Params? = null) = execute(params).flowOn(dispatcher)
}
Here is the dependency :
object Pagination {
object Version {
const val pagingCompose = "1.0.0-alpha14"
}
const val pagingCompose = "androidx.paging:paging-compose:${Version.pagingCompose}"
}
I'm assuming that filterPreferences gives you Flow of some preference and useCase.execute returns Flow<PagingData<Model>>, correct?
I believe that the problem is in usage of flatMapLatest - it mixes page events of multiple useCase.execute calls together.
You should do something like this:
val games: Flow<Flow<PagingData<GameModel>>> = filterPreferences.mapLatest {
useCase.execute(it)
}.mapLatest {
it.map { pagingData -> pagingData.map { GameModel.GameItem(it) } }
}.mapLatest {
it.map { pagingData ->
pagingData.insertSeparators { before, after -> ... }
} // .cachedIn(viewModelScope)
}
This same structure works for us very well. I'm only not sure how cachedIn will work here, we are using a different caching mechanism, but you can try.
PROBLEM STATEMENT
: When i press register button for register new user it show register success response in toast from live data, but when i tried to do same button trigger it show again register success response message from API & then also show phone number exist response from API in toast. It means old response return by live data too. So how can i solve this recursive live data response return issue?
HERE is the problem video link to understand issue
Check here https://drive.google.com/file/d/1-hKGQh9k0EIYJcbInwjD5dB33LXV5GEn/view?usp=sharing
NEED ARGENT HELP
My Api Interface
interface ApiServices {
/*
* USER LOGIN (GENERAL USER)
* */
#POST("authentication.php")
suspend fun loginUser(#Body requestBody: RequestBody): Response<BaseResponse>
}
My Repository Class
class AuthenticationRepository {
var apiServices: ApiServices = ApiClient.client!!.create(ApiServices::class.java)
suspend fun UserLogin(requestBody: RequestBody) = apiServices.loginUser(requestBody)
}
My View Model Class
class RegistrationViewModel : BaseViewModel() {
val respository: AuthenticationRepository = AuthenticationRepository()
private val _registerResponse = MutableLiveData<BaseResponse>()
val registerResponse: LiveData<BaseResponse> get() = _registerResponse
/*
* USER REGISTRATION [GENERAL USER]
* */
internal fun performUserLogin(requestBody: RequestBody, onSuccess: () -> Unit) {
ioScope.launch {
isLoading.postValue(true)
tryCatch({
val response = respository.UserLogin(requestBody)
if (response.isSuccessful) {
mainScope.launch {
onSuccess.invoke()
isLoading.postValue(false)
_registerResponse.postValue(response.body())
}
} else {
isLoading.postValue(false)
}
}, {
isLoading.postValue(false)
hasError.postValue(it)
})
}
}
}
My Registration Activity
class RegistrationActivity : BaseActivity<ActivityRegistrationBinding>() {
override val layoutRes: Int
get() = R.layout.activity_registration
private val viewModel: RegistrationViewModel by viewModels()
override fun onCreated(savedInstance: Bundle?) {
toolbarController()
viewModel.isLoading.observe(this, {
if (it) showLoading(true) else showLoading(false)
})
viewModel.hasError.observe(this, {
showLoading(false)
showMessage(it.message.toString())
})
binding.registerbutton.setOnClickListener {
if (binding.registerCheckbox.isChecked) {
try {
val jsonObject = JSONObject()
jsonObject.put("type", "user_signup")
jsonObject.put("user_name", binding.registerName.text.toString())
jsonObject.put("user_phone", binding.registerPhone.text.toString())
jsonObject.put("user_password", binding.registerPassword.text.toString())
val requestBody = jsonObject.toString()
.toRequestBody("application/json; charset=utf-8".toMediaTypeOrNull())
viewModel.performUserLogin(requestBody) {
viewModel.registerResponse.observe(this){
showMessage(it.message.toString())
//return old reponse here then also new reponse multiple time
}
}
} catch (e: JSONException) {
e.printStackTrace()
}
} else {
showMessage("Please Accept Our Terms & Conditions")
}
}
}
override fun toolbarController() {
binding.backactiontoolbar.menutitletoolbar.text = "Registration"
binding.backactiontoolbar.menuicontoolbar.setOnClickListener { onBackPressed() }
}
override fun processIntentData(data: Uri) {}
}
your registerResponse live data observe inside button click listener, so that's why it's observing two times! your registerResponse live data should observe data out side of button Click listener -
override fun onCreated(savedInstance: Bundle?) {
toolbarController()
viewModel.isLoading.observe(this, {
if (it) showLoading(true) else showLoading(false)
})
viewModel.registerResponse.observe(this){
showMessage(it.message.toString())
}
viewModel.hasError.observe(this, {
showLoading(false)
showMessage(it.message.toString())
})
binding.registerbutton.setOnClickListener {
if (binding.registerCheckbox.isChecked) {
try {
val jsonObject = JSONObject()
jsonObject.put("type", "user_signup")
jsonObject.put("user_name", binding.registerName.text.toString())
jsonObject.put("user_phone", binding.registerPhone.text.toString())
jsonObject.put("user_password", binding.registerPassword.text.toString())
val requestBody = jsonObject.toString()
.toRequestBody("application/json; charset=utf-8".toMediaTypeOrNull())
viewModel.performUserLogin(requestBody) {
}
} catch (e: JSONException) {
e.printStackTrace()
}
} else {
showMessage("Please Accept Our Terms & Conditions")
}
}
}
LiveData is a state holder, it's not really meant to be used as an event stream. There is a number of articles however about the topic like this one which describe the possible solutions, including SingleLiveEvent implementation taken from google samples.
But as of now kotlin coroutines library provides better solutions. In particular, channels are very useful for event streams, because they implement fan-out behaviour, so you can have multiple event consumers, but each event will be handled only once. Channel.receiveAsFlow can be very convenient to expose the stream as flow. Otherwise, SharedFlow is a good candidate for event bus implementation. Just be careful with replay and extraBufferCapacity parameters.
I have issue with the following code:
suspend fun getData(): Flow<Resource<User>> {
println("#getData called")
return channelFlow {
println("#getData producer scope started")
launch(Dispatchers.IO) {
val cachedData = sharedPreferencesUtils.getData()
println("#getData send cached data")
send(cachedData)
}
launch(Dispatchers.IO) {
val response = handleAPI<EducationResponse> { apiService.getData() }
println("#getData send remote data")
send(response)
}
}
}
Above code is working most times and send data from local and remote, but sometimes the producer scope not triggered (it print "#getData called" only)
Please advice!
UPDATE:
and the Flow collected:
CoroutineScope(Dispatchers.IO).launch(AppExceptionHandler.exceptionHandler) {
prescriptionsRepository
.getData()
.collect {
educationWithSponsorsLiveData.postValue(it)
}
}
Hello I'm using RxAndroidBLE to detect a BLE device. On android 6 >= everything seems to work okay but not on a 4.3 device.
My app can only discover the desirable BLE device only once at start. After the device has been discovered no more new discoveries at all until I restart the app. Any advice would be highly appreciated.
Below minimum (not)working code example:
MainActivity
import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.os.Handler
import android.util.Log
import com.polidea.rxandroidble.RxBleClient
import com.polidea.rxandroidble.exceptions.BleScanException
import com.polidea.rxandroidble.scan.ScanResult
import com.polidea.rxandroidble.scan.ScanSettings
import rx.Subscription
import rx.android.schedulers.AndroidSchedulers
import java.util.*
import java.util.concurrent.Executors
import java.util.concurrent.TimeUnit
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
startLeScan(applicationContext)
}
private var rxBleClient: RxBleClient? = null
private var scanSubscription: Subscription? = null
private var handler: Handler? = null
private var timer: Timer? = null
private var timerTask: TimerTask? = null
private var delay: Int = 0
private fun isScanning(): Boolean {
return scanSubscription != null
}
fun startLeScan(context: Context) {
rxBleClient = MyaPP.getRxBleClient(context)
if (isScanning()) {
scanSubscription?.unsubscribe()
} else {
scanSubscription = rxBleClient?.scanBleDevices(
com.polidea.rxandroidble.scan.ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
.build())
?.observeOn(AndroidSchedulers.mainThread())
//?.doOnNext(this::newDevicesFound)
?.doOnUnsubscribe(this::clearSubscription)
?.subscribe(this::newDevicesFound, this::onScanFailure)
}
if(handler == null) {
handler = Handler()
timer = Timer(false)
timerTask = object : TimerTask() {
override fun run() {
handler?.post {
if (delay > 7) {
delay = 0
val service = Executors.newSingleThreadExecutor()
service.submit(Runnable {
//startLeScan(context)
})
} else {
delay = delay + 1
}
}
}
}
timer?.scheduleAtFixedRate(timerTask, 0, 300)
}
}
private fun newDevicesFound(devices: ScanResult) {
Log.d("WHYY??", devices.bleDevice.name)
}
fun stopScan() {
scanSubscription?.unsubscribe()
destroy()
}
private fun clearSubscription() {
scanSubscription = null
}
private fun onScanFailure(throwable: Throwable) {
if (throwable is BleScanException) {
handleBleScanException(throwable)
}
}
private fun handleBleScanException(bleScanException: BleScanException) {
val text: String
when (bleScanException.reason) {
BleScanException.BLUETOOTH_NOT_AVAILABLE -> text = "Bluetooth is not available"
BleScanException.BLUETOOTH_DISABLED -> text = "Enable bluetooth and try again"
BleScanException.LOCATION_PERMISSION_MISSING -> text = "On Android 6.0 location permission is required. Implement Runtime Permissions"
BleScanException.LOCATION_SERVICES_DISABLED -> text = "Location services needs to be enabled on Android 6.0"
BleScanException.SCAN_FAILED_ALREADY_STARTED -> text = "Scan with the same filters is already started"
BleScanException.SCAN_FAILED_APPLICATION_REGISTRATION_FAILED -> text = "Failed to register application for bluetooth scan"
BleScanException.SCAN_FAILED_FEATURE_UNSUPPORTED -> text = "Scan with specified parameters is not supported"
BleScanException.SCAN_FAILED_INTERNAL_ERROR -> text = "Scan failed due to internal error"
BleScanException.SCAN_FAILED_OUT_OF_HARDWARE_RESOURCES -> text = "Scan cannot start due to limited hardware resources"
BleScanException.UNDOCUMENTED_SCAN_THROTTLE -> text = String.format(
Locale.getDefault(),
"Android 7+ does not allow more scans. Try in %d seconds",
secondsTill(bleScanException.retryDateSuggestion)
)
BleScanException.UNKNOWN_ERROR_CODE, BleScanException.BLUETOOTH_CANNOT_START -> text = "Unable to start scanning"
else -> text = "Unable to start scanning"
}
Log.w("EXCEPTION", text, bleScanException)
}
private fun secondsTill(retryDateSuggestion: Date?): Long {
if (retryDateSuggestion != null) {
return TimeUnit.MILLISECONDS.toSeconds(retryDateSuggestion.time - System.currentTimeMillis())
}
return 0
}
private fun destroy() {
timer?.cancel()
handler?.removeCallbacks(timerTask)
handler = null
timerTask = null
timer = null
}
}
MyaPP
import android.app.Application
import android.content.Context
import com.polidea.rxandroidble.RxBleClient
import com.polidea.rxandroidble.internal.RxBleLog
class MyaPP: Application() {
private var rxBleClient: RxBleClient? = null
companion object {
fun getRxBleClient(context: Context): RxBleClient? {
val application = context.applicationContext as MyaPP
return application.rxBleClient
}
}
override fun onCreate() {
super.onCreate()
rxBleClient = RxBleClient.create(this)
RxBleClient.setLogLevel(RxBleLog.DEBUG)
}
}
build.gradle
compile "com.polidea.rxandroidble:rxandroidble:1.5.0"
implementation 'io.reactivex:rxandroid:1.2.1'
manifest
<application
android:name=".MyaPP"
Your code looks a lot like the library's sample app (version 1.5.0, branch master-rxjava1). I have checked that recently on Android 4.4.4 which is the oldest I have and it worked fine. There were no API changes between 4.3 and 4.4.
What you may be experiencing is a behaviour specific to your device (feel free to share your phone model) in which it only callbacks for the first time it scans a particular peripheral. There are some threads about this topic already like this one.
I am using kotlin coroutines for network request using extension method to call class in retrofit like this
public suspend fun <T : Any> Call<T>.await(): T {
return suspendCancellableCoroutine { continuation ->
enqueue(object : Callback<T> {
override fun onResponse(call: Call<T>?, response: Response<T?>) {
if (response.isSuccessful) {
val body = response.body()
if (body == null) {
continuation.resumeWithException(
NullPointerException("Response body is null")
)
} else {
continuation.resume(body)
}
} else {
continuation.resumeWithException(HttpException(response))
}
}
override fun onFailure(call: Call<T>, t: Throwable) {
// Don't bother with resuming the continuation if it is already cancelled.
if (continuation.isCancelled) return
continuation.resumeWithException(t)
}
})
registerOnCompletion(continuation)
}
}
then from calling side i am using above method like this
private fun getArticles() = launch(UI) {
loading.value = true
try {
val networkResult = api.getArticle().await()
articles.value = networkResult
}catch (e: Throwable){
e.printStackTrace()
message.value = e.message
}finally {
loading.value = false
}
}
i want to exponential retry this api call in some case i.e (IOException) how can i achieve it ??
I would suggest to write a helper higher-order function for your retry logic. You can use the following implementation for a start:
suspend fun <T> retryIO(
times: Int = Int.MAX_VALUE,
initialDelay: Long = 100, // 0.1 second
maxDelay: Long = 1000, // 1 second
factor: Double = 2.0,
block: suspend () -> T): T
{
var currentDelay = initialDelay
repeat(times - 1) {
try {
return block()
} catch (e: IOException) {
// you can log an error here and/or make a more finer-grained
// analysis of the cause to see if retry is needed
}
delay(currentDelay)
currentDelay = (currentDelay * factor).toLong().coerceAtMost(maxDelay)
}
return block() // last attempt
}
Using this function is very strightforward:
val networkResult = retryIO { api.getArticle().await() }
You can change retry parameters on case-by-case basis, for example:
val networkResult = retryIO(times = 3) { api.doSomething().await() }
You can also completely change the implementation of retryIO to suit the needs of your application. For example, you can hard-code all the retry parameters, get rid of the limit on the number of retries, change defaults, etc.
Here an example with the Flow and the retryWhen function
RetryWhen Extension :
fun <T> Flow<T>.retryWhen(
#FloatRange(from = 0.0) initialDelay: Float = RETRY_INITIAL_DELAY,
#FloatRange(from = 1.0) retryFactor: Float = RETRY_FACTOR_DELAY,
predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long, delay: Long) -> Boolean
): Flow<T> = this.retryWhen { cause, attempt ->
val retryDelay = initialDelay * retryFactor.pow(attempt.toFloat())
predicate(cause, attempt, retryDelay.toLong())
}
Usage :
flow {
...
}.retryWhen { cause, attempt, delay ->
delay(delay)
...
}
Here's a more sophisticated and convenient version of my previous answer, hope it helps someone:
class RetryOperation internal constructor(
private val retries: Int,
private val initialIntervalMilli: Long = 1000,
private val retryStrategy: RetryStrategy = RetryStrategy.LINEAR,
private val retry: suspend RetryOperation.() -> Unit
) {
var tryNumber: Int = 0
internal set
suspend fun operationFailed() {
tryNumber++
if (tryNumber < retries) {
delay(calculateDelay(tryNumber, initialIntervalMilli, retryStrategy))
retry.invoke(this)
}
}
}
enum class RetryStrategy {
CONSTANT, LINEAR, EXPONENTIAL
}
suspend fun retryOperation(
retries: Int = 100,
initialDelay: Long = 0,
initialIntervalMilli: Long = 1000,
retryStrategy: RetryStrategy = RetryStrategy.LINEAR,
operation: suspend RetryOperation.() -> Unit
) {
val retryOperation = RetryOperation(
retries,
initialIntervalMilli,
retryStrategy,
operation,
)
delay(initialDelay)
operation.invoke(retryOperation)
}
internal fun calculateDelay(tryNumber: Int, initialIntervalMilli: Long, retryStrategy: RetryStrategy): Long {
return when (retryStrategy) {
RetryStrategy.CONSTANT -> initialIntervalMilli
RetryStrategy.LINEAR -> initialIntervalMilli * tryNumber
RetryStrategy.EXPONENTIAL -> 2.0.pow(tryNumber).toLong()
}
}
Usage:
coroutineScope.launch {
retryOperation(3) {
if (!tryStuff()) {
Log.d(TAG, "Try number $tryNumber")
operationFailed()
}
}
}
Flow Version https://github.com/hoc081098/FlowExt
package com.hoc081098.flowext
import kotlin.time.Duration
import kotlin.time.ExperimentalTime
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.FlowCollector
import kotlinx.coroutines.flow.emitAll
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.retryWhen
#ExperimentalTime
public fun <T> Flow<T>.retryWithExponentialBackoff(
initialDelay: Duration,
factor: Double,
maxAttempt: Long = Long.MAX_VALUE,
maxDelay: Duration = Duration.INFINITE,
predicate: suspend (cause: Throwable) -> Boolean = { true }
): Flow<T> {
require(maxAttempt > 0) { "Expected positive amount of maxAttempt, but had $maxAttempt" }
return retryWhenWithExponentialBackoff(
initialDelay = initialDelay,
factor = factor,
maxDelay = maxDelay
) { cause, attempt -> attempt < maxAttempt && predicate(cause) }
}
#ExperimentalTime
public fun <T> Flow<T>.retryWhenWithExponentialBackoff(
initialDelay: Duration,
factor: Double,
maxDelay: Duration = Duration.INFINITE,
predicate: suspend FlowCollector<T>.(cause: Throwable, attempt: Long) -> Boolean
): Flow<T> = flow {
var currentDelay = initialDelay
retryWhen { cause, attempt ->
predicate(cause, attempt).also {
if (it) {
delay(currentDelay)
currentDelay = (currentDelay * factor).coerceAtMost(maxDelay)
}
}
}.let { emitAll(it) }
}
You can try this simple but very agile approach with simple usage:
EDIT: added a more sophisticated solution in a separate answer.
class Completion(private val retry: (Completion) -> Unit) {
fun operationFailed() {
retry.invoke(this)
}
}
fun retryOperation(retries: Int,
dispatcher: CoroutineDispatcher = Dispatchers.Default,
operation: Completion.() -> Unit
) {
var tryNumber = 0
val completion = Completion {
tryNumber++
if (tryNumber < retries) {
GlobalScope.launch(dispatcher) {
delay(TimeUnit.SECONDS.toMillis(tryNumber.toLong()))
operation.invoke(it)
}
}
}
operation.invoke(completion)
}
The use it like this:
retryOperation(3) {
if (!tryStuff()) {
// this will trigger a retry after tryNumber seconds
operationFailed()
}
}
You can obviously build more on top of it.