LiveData observer does not trigger on a callback - android

LiveData observer does not trigger when a callback is emitted. But if I put the observable data in a function and change the data it works just fine. Please any ideas what would it be?
fun connect(address: String){
protocolARC.value = ProtocolARC() //OKAY!!!!
bleManager.gattClient.onCreate(getApplication(), address, object : GattClient.OnCounterReadListener {
override fun onCounterRead(value: Int) {
Log.d("HURRAY", "read")
protocolARC.value = ProtocolARC() //NOT OKAY?????
}
override fun onConnected(success: Boolean) {
stopScan()
}
})
}

The problem was in a callback. It was not being triggered from the main thread.

Related

How to convert custom callback to coroutine

I am using Stripe library which provides me with custom callback functionality.
I want a custom callback convert to Kotlin coroutine
Here is the code
override fun retrievePaymentIntent(clientSecret: String): Flow<Resource<PaymentIntent>> = flow{
emit(Resource.Loading())
Terminal.getInstance().retrievePaymentIntent(clientSecret,
object : PaymentIntentCallback {
override fun onFailure(e: TerminalException) {}
override fun onSuccess(paymentIntent: PaymentIntent) {
emit(Resource.Success(paymentIntent))
}
})
}
The problem is I can't call emit function inside onSuccess/onFailure. The error shown in the picture.
Is it possible to change something here to make it work or how could I convert custom callback to coroutine?
You can use suspendCancellableCoroutine to model your callback-based one-shot request like so:
suspend fun retrievePaymentIntent(clientSecret: String): PaymentIntent =
suspendCancellableCoroutine { continuation ->
Terminal.getInstance().retrievePaymentIntent(clientSecret,
object : PaymentIntentCallback {
override fun onFailure(e: TerminalException)
{
continuation.resumeWithException(e)
}
override fun onSuccess(paymentIntent: PaymentIntent)
{
continuation.resume(paymentIntent)
}
})
continuation.invokeOnCancellation { /*cancel the payment intent retrieval if possible*/ }
}

GeoFire removeAllListeners() method not removing the listener at all

I have a geofire query that gets the nearby users. Everything is working fine but I want to stop listening to new events if the pagingCounter reaches certain limit. I have added geoQuery.removeAllListeners() in onKeyEntered() method but that is not removing the listener. The events are still getting and onKeyEntered() method keeps getting called until it reads all the elements in DB.
Please help me identify what I am doing wrong. Thanks in advance!
var pagingCounter = 0
val geoQuery = geoFire.queryAtLocation(GeoLocation(mainUserLatitude, mainUserLongitude), distanceInKm)
geoQuery.addGeoQueryEventListener(object : GeoQueryEventListener {
override fun onGeoQueryReady() {
for ((key, value) in nearByUsersKeysTreeMap) {
val singleUserDatabaseReference = database.child(Constants.users).child(key)
singleUserDatabaseReference.addListenerForSingleValueEvent(object : ValueEventListener {
override fun onCancelled(p0: DatabaseError) {
}
override fun onDataChange(dataSnapshot: DataSnapshot) {
}
})
}
}
override fun onKeyEntered(key: String?, location: GeoLocation?) {
pagingCounter++
if (pagingCounter >= 100) {
geoQuery.removeAllListeners()
}
}
override fun onKeyMoved(key: String?, location: GeoLocation?) {
}
override fun onKeyExited(key: String?) {
}
override fun onGeoQueryError(error: DatabaseError?) {
}
})
If these are all keys that are initially in range, then what you're seeing is the expected behavior. Retrieving all keys that are initially in range from the database is an operation that can't be interrupted.
Calling removeAllListeners prevents retrieving further updates to the keys from the database, but the client will still fire events for all listeners for which it has already received data.
If you want to no longer respond to those events, you can use a field that you set when you call removeAllListeners and then check for that field's value in the onKey* methods.

RxJava BehaviorSubject subcribeoN

Below Code
why onnext called only once? When I remove subscribeOn it was called for every number.
when I subscribeOn io thread just once called (for 8658)
can someone explain it to me?
val subject = BehaviorSubject.create<Int>()
subject.onNext(2121)
subject.distinctUntilChanged().doOnNext {
Log.d("AHMET VEFA SARUHAN", it.toString())
}.subscribeOn(Schedulers.io()).subscribe(object : Observer<Int> {
override fun onSubscribe(d: Disposable?) {
}
override fun onNext(t: Int?) {
}
override fun onError(e: Throwable?) {
}
override fun onComplete() {
}
})
subject.onNext(5436)
subject.onNext(8658)
By using subscribeOn, the chain to observe the BehaviorSubject is established concurrently with the thread calling the onNexts. It takes time for a subscribeOn to take effect thus the main thread simply runs ahead and overwrites the subject's current value to the latest in the meantime.
There is no practical reason to use subscribeOn on a Subject in general.

Wait For Data Inside a Listener in a Coroutine

I have a coroutine I'd like to fire up at android startup during the splash page. I'd like to wait for the data to come back before I start the next activity. What is the best way to do this? Currently our android is using experimental coroutines 0.26.0...can't change this just yet.
UPDATED: We are now using the latest coroutines and no longer experimental
onResume() {
loadData()
}
fun loadData() = GlobalScope.launch {
val job = GlobalScope.async {
startLibraryCall()
}
// TODO await on success
job.await()
startActivity(startnewIntent)
}
fun startLibraryCall() {
val thirdPartyLib() = ThirdPartyLibrary()
thirdPartyLib.setOnDataListener() {
///psuedocode for success/ fail listeners
onSuccess -> ///TODO return data
onFail -> /// TODO return other data
}
}
The first point is that I would change your loadData function into a suspending function instead of using launch. It's better to have the option to define at call site how you want to proceed with the execution. For example when implementing a test you may want to call your coroutine inside a runBlocking. You should also implement structured concurrency properly instead of relying on GlobalScope.
On the other side of the problem I would implement an extension function on the ThirdPartyLibrary that turns its async calls into a suspending function. This way you will ensure that the calling coroutine actually waits for the Library call to have some value in it.
Since we made loadData a suspending function we can now ensure that it will only start the new activity when the ThirdPartyLibrary call finishes.
import kotlinx.coroutines.*
import kotlin.coroutines.*
class InitialActivity : AppCompatActivity(), CoroutineScope {
private lateinit var masterJob: Job
override val coroutineContext: CoroutineContext
get() = Dispatchers.Main + masterJob
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
masterJob = Job()
}
override fun onDestroy() {
super.onDestroy()
masterJob.cancel()
}
override fun onResume() {
this.launch {
val data = ThirdPartyLibrary().suspendLoadData()
// TODO: act on data!
startActivity(startNewIntent)
}
}
}
suspend fun ThirdPartyLibrary.suspendLoadData(): Data = suspendCoroutine { cont ->
setOnDataListener(
onSuccess = { cont.resume(it) },
onFail = { cont.resumeWithException(it) }
)
startLoadingData()
}
You can use LiveData
liveData.value = job.await()
And then add in onCreate() for example
liveData.observe(currentActivity, observer)
In observer just wait until value not null and then start your new activity
Observer { result ->
result?.let {
startActivity(newActivityIntent)
}
}

RxJava not running on Background thread

I am trying to save data in Room and it requires some background thread to save data. So I have created an observable like this
val obs: Observable<MutableLiveData<List<Source>>>? = Observable.fromCallable(object :Callable<MutableLiveData<List<Source>>>{
override fun call(): MutableLiveData<List<Source>> {
return mutableLiveData
}
})
Then I am subscribing, observing and unsubscribing it like this
obs?.subscribeOn(Schedulers.io())?.observeOn(AndroidSchedulers.mainThread())?.unsubscribeOn(Schedulers.io())
?.subscribe(object : Observer<MutableLiveData<List<Source>>>{
override fun onComplete() {
}
override fun onSubscribe(d: Disposable?) {
}
override fun onNext(value: MutableLiveData<List<Source>>?) {
for(source in value!!.value!!.iterator()){
sourceDao.insert(source)//this is the line number 87, that logcat is pointing
}
}
override fun onError(e: Throwable?) {
e?.printStackTrace()
}
})
I am subscribing it on the Schedulers.io thread then observing it on the AndroidSchedulers.mainThread() but still I am getting not on background thread error. More specifically
Caused by: java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.
at android.arch.persistence.room.RoomDatabase.assertNotMainThread(RoomDatabase.java:204)
at android.arch.persistence.room.RoomDatabase.beginTransaction(RoomDatabase.java:251)
06-18 11:11:08.674 3732-3732/com.theanilpaudel.technewspro W/System.err: at com.package.myapp.room.SourceDao_Impl.insert(SourceDao_Impl.java:63)
at com.package.myapp.main.MainRepository$saveToRoom$1.onNext(MainRepository.kt:87)
at com.package.myapp.main.MainRepository$saveToRoom$1.onNext(MainRepository.kt:76)
Execute your DB operation within the Observable and not in your Observer:
val obs: Observable<MutableLiveData<List<Source>>>? = Observable.fromCallable(object :Callable<MutableLiveData<List<Source>>>{
override fun call(): MutableLiveData<List<Source>> {
for(source in mutableLiveData!!.value!!.iterator()){
sourceDao.insert(source)
}
return mutableLiveData
})
.subscribeOn(Schedulers.io())?.observeOn(AndroidSchedulers.mainThread())?.unsubscribeOn(Schedulers.io())
?.subscribe(object : Observer<MutableLiveData<List<Source>>>{
override fun onComplete() {
}
override fun onSubscribe(d: Disposable?) {
}
override fun onNext(value: MutableLiveData<List<Source>>?) {
// Nothing todo right more
}
override fun onError(e: Throwable?) {
e?.printStackTrace()
}
})
})
It makes sense because you have observeOn the main thread and you are doing your work in the observer (observeOn manages the thread of the observer).
To fix this, you can use flatmap on your obs and do the for loop in there. Since flatmap requires you to return an Observable, you can return Observable.just(true) after your for loop.

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