private val timer = object : CountDownTimer(result, 1000) {
override fun onFinish() {
//delete the database entry
}
override fun onTick(millisUntilFinished: Long) {
//more code
}
}
As far as my knowledge in kotlin, object gets called before the result gets assigned a value
Initially, the result value is 0, then it gets updated in another function, but the timer gets called with result value as 0.
So what should be the best replacement for object here?
You can keep object, you just need to change order of initialization. One way would be to use by lazy, like this:
var result = 0L
private val timer: CountDownTimer by lazy {
object : CountDownTimer(result, 1000) {
override fun onFinish() {
// delete the database entry
}
override fun onTick(millisUntilFinished: Long) {
// more code
}
}
}
// 'init' block just as an example; the below code works anywhere
// such as in onCreate(), onStart() or wherever
init {
result = 1000
// 'timer' is initialized with result=1000 and then started
timer.start()
}
lazy is a so called property delegate, you can read more about it in the official docs for example.
I don't see how this is related to Kotlin?
You have a member val: timer
It is initialized when the object, the val resides in, is created.
So the problem is not what syntax you are using. It is the time you create timer. If you know when you are going to use it, and you are sure that by this time the result will be intialized, you can use lazy initialization.
Related
So I'm writing a piece of code to add a pause and resume functionality into the abstract class CountDownTimer (Android.os.CountDownTimer). I'm using the functionality only within this one activity and therefore am just using an object expression to create an anonymous class called sequencetimer. The code looks something like this:
public var sequencetimer = object : CountDownTimer(30000, 1000) {
public var timeremaining : Long = 0
override fun onTick(millisUntilFinished: Long) {
findViewById<TextView>(R.id.textView8).apply {
text = ("seconds remaining: " + millisUntilFinished / 1000)
}
}
override fun onFinish() {
findViewById<TextView>(R.id.textView8).apply {
text = "done"
}
}
public fun pauseTimer() {
timeremaining = findViewById<TextView>(R.id.textView8).text as Long
cancel()
}
public fun resumeTimer() {
onTick(timeremaining)
start()
}
}
Now I want to call the pauseTimer and resumeTimer functions that I added whenever my activity pauses or resumes like so:
override fun onPause() {
super.onPause()
sequencetimer.pauseTimer()
}
override fun onResume() {
super.onResume()
sequencetimer.resumeTimer()
}
The code however keeps throwing me an unresolved reference error for the functions pauseTimer() and resumeTimer(), even though the sequencetimer object is declared within the activity class and I can execute all the other functions such as sequencetimer.onTick() and sequencetimer.start() (however I can also not acces the public var timeremaining). Does anyone have any idea what the issue here is? Or is it simply not possible to expand/extend an abstract class within an anonymous object expression (I would have expected android studio to then throw some type of error)?
As you said yourself: you create anonymous class. That means this class doesn't exists from the developer point of view and the type of sequencetimer is just CountDownTimer which doesn't have pauseTimer() and resumeTimer() functions. You need to create a regular, named class, so it can be referenced in the code.
Alternatively, you can make sequencetimer a private var. In this case Kotlin assumes this is internal stuff and provides some kind of a shortcut. It conditionally permits this kind of operation, even if normally it should not be possible. This behavior is described in the docs: https://kotlinlang.org/docs/object-declarations.html#using-anonymous-objects-as-return-and-value-types
There are some issues with your code.
First issue I see is that public var sequencetimer. With kotlin keywords public, protected, internal you declare to compiler that sequencetimer would be accessible outside of your android activity class's scope. But object created as anonymous class in your activity class. Kotlin compiler decides that the only solution is marking sequencetimer as CountDownTimer.
// byte code
public final getSequencetimer()Landroid/os/CountDownTimer;
#Lorg/jetbrains/annotations/NotNull;()
Secondly, resumeTimer() will call onTick(12345L) once and restart the timer from the millisInFuture 30_000L.
It would be better you create a new count down timer for the remaining time.
And please, decrease the count down interval or you will see the seconds inconsistent 30, 28, 27, 26, 26, 24, ...
Hope, it helps.
I have an IOTCamera function inside viewModel with Loop. The function should repeatedly call the repository GET function based on the "selectedSlot" parameter with a delay of 1 minute. My problem here is the loop(repeat()) is not working properly. It's working for the first iteration. But the second iteration never gets called.
fun getIOTCameraData(repository: MainRepository, selectedSlot: Int)= viewModelScope.launch(Dispatchers.Default){
repeat(selectedSlot){
repository.getIOTCameraData(1, 10).asFlow().collect {data->
if (responseStatusIdentification(data)) {
_iotCameraData.postValue(data.data)//Update live data instance for UI
}
}
delay(60000)
}
}
The repository function will call the Retrofit GET API and it will collect the data.
suspend fun getIOTCameraData(page: Int, perPage: Int) = liveData<Resource<IOTCameraResponse>> {
emit(Resource.loading())
try {
val response = iotCameraService?.getIOTCameraData(token = IOT_CAMERA_AUTH, page = page, perPage = perPage)
emit(Resource.success(response))
} catch (e: Exception) {
emit(Resource.error(e.message.toString()))
}
}
Please update if anyone know the reason for this.
The call to collect never returns. If you just need to get a single value and end collecting then you should call first() instead.
Like this:
val data = repository.getIOTCameraData(1, 10).asFlow().first {
responseStatusIdentification(it)
}
_iotCameraData.postValue(data.data)
I checked the other questions but none of them seem to address my issue.
I have two suspend funs in my HomeViewModel and I'm calling them in my HomeFragment (with a spinner text parameter).
The two suspend functions in HomeViewModel:
suspend fun tagger(spinner: Spinner){
withContext(Dispatchers.IO){
val vocab: String = inputVocab.value!!
var tagger = Tagger(
spinner.getSelectedItem().toString() + ".tagger"
)
val sentence = tagger.tagString(java.lang.String.valueOf(vocab))
tagAll(sentence)
}
}
suspend fun tagAll(vocab: String){
withContext(Dispatchers.IO){
if (inputVocab.value == null) {
statusMessage.value = Event("Please enter sentence")
}
else {
insert(Vocab(0, vocab))
inputVocab.value = null
}
}
}
and this is how I call them in the HomeFragment:
GlobalScope.launch (Dispatchers.IO) {
button.setOnClickListener {
homeViewModel.tagger(binding.spinner)
}
}
At tagger I get the error "Suspension functions can be called only within coroutine body". But it's already inside a global scope. How can I avoid this problem?
But it's already inside a global scope.
The call to button.onSetClickListener() is in a launched coroutine from a CoroutineScope. However, the lambda expression that you are passing to onSetClickListener() is a separate object, mapped to a separate onClick() function, and that function call is not part of that coroutine.
You would need to change this to:
button.setOnClickListener {
GlobalScope.launch (Dispatchers.IO) {
homeViewModel.tagger(binding.spinner)
}
}
BTW, you may wish to review Google's best practices for coroutines in Android, particularly "The ViewModel should create coroutines".
I hope to get the total of all records with Room database at once. But, normally Room use background thread to query record asynchronously.
If I use getTotalOfVoiceAsLiveData() in Code A, it will return LiveData<Long>, you know that LiveData variable is lazy, maybe the result is null.
If I use getTotalOfVoice() in Code A, I will get error because I can't use return in viewModelScope.launch{ }.
How can I get the total of all records at once with Room database?
Code A
class HomeViewModel(val mApplication: Application, private val mDBVoiceRepository: DBVoiceRepository) : AndroidViewModel(mApplication) {
fun getTotalOfVoice():Long {
viewModelScope.launch {
return mDBVoiceRepository.getTotalOfVoice() //It will cause error
}
}
fun getTotalOfVoiceAsLiveData(): LiveData<Long>{
return mDBVoiceRepository.getTotalOfVoiceAsLiveData() //It's lazy, maybe the result is null.
}
}
class DBVoiceRepository private constructor(private val mDBVoiceDao: DBVoiceDao){
suspend fun getTotalOfVoice() = mDBVoiceDao.getTotalOfVoice()
fun getTotalOfVoiceAsLiveData() = mDBVoiceDao.getTotalOfVoiceAsLiveData()
}
#Dao
interface DBVoiceDao{
#Query("SELECT count(id) FROM voice_table")
suspend fun getTotalOfVoice(): Long
//When Room queries return LiveData, the queries are automatically run asynchronously on a background thread.
#Query("SELECT count(id) FROM voice_table")
fun getTotalOfVoiceAsLiveData(): LiveData<Long>
}
Add content
To Tobi: Thanks!
Why it is important to you to get the data directly?
I need to generate a filename based the total of the records, such as "untitled0", "untitled1", "untitled2"...
If I can get the query result at once, I can use the following code easyly.
Added again
I hope to record a voice by filename based the total of query records when I click Start button. You know the total of records will change when a reocrd is added or deleted!
Code B
fun getTotalOfVoice():Long {
//Get the query result at once
...
}
fun createdFileanme(){
return "untitled"+getTotalOfVoice().toString()
}
btnStart.setOnClickListener{
recordVoice(createdFileanme()) //I will record voice by filename
}
fun addRecord(){
...
}
fun deleteRecord(){
...
}
New added content
Thanks!
I think 'You should also move all of that into the viewmodel class, without LiveData ' is good way, you can see Image A and How can I get the value of a LivaData<String> at once in Android Studio? .
Do you agree with it?
Image A
Question: at once meaning synchronous or what ? if yes, what happens if the function to get the result has to take a longer time? like network call? well you can decide to do that on another thread.
What I think is for you to use a mutable Object and use the postValue function to dispatch the result to the observers. It should look something like below:
class HomeViewModel(val mApplication: Application, private val mDBVoiceRepository: DBVoiceRepository) : AndroidViewModel(mApplication) {
private val voices = MutableLiveData<Long>()
fun getTotalOfVoiceAsLiveData(): LiveData<Long> {
voices.postValue(mDBVoiceRepository.getTotalOfVoiceAsLiveData().value)
return voices;
}
}
Making use of it in your Fragment will look like below:
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
if (activity != null) {
val viewModel = ViewModelProvider(requireActivity())
viewModel.get(HomeViewModel::class.java).getTotalOfVoiceAsLiveData().observe(viewLifecycleOwner, Observer { voices: Long ? ->
voices // Sound of music ? be very free to use ...
})
}
}
Happy Coding.
I hope to get the result at once, but LiveData is lazy
Sorry to tell, but this is how the Room interface is designed.
You are right with the lazyness of the returned LiveData object. But this allows you to handle it on a different thread without having to manually handle different threads.
Based on your new information!
You basically have two options:
A) you could do the following:
load data from Room via LivaData
add observer that stores the current total amount
when the button is clicked you just read the local copy
In your View: (only one observer and one clickListener)
val totalVoiceCount: long
val viewModel = ViewModelProvider(requireActivity()).get(HomeViewModel::class.java)
viewModel.getTotalOfVoiceAsLiveData().observe(viewLifecycleOwner, Observer { totalOfVoice : Long ? ->
if (totalOfVoice != null)
totalVoiceCount = totalOfVoice
})
btnStart.setOnClickListener{
viewModel.recordVoice(totalVoiceCount)
}
In your ViewModel: (the logic and everything else)
fun recordVoice(totalVoiceCount : long){
val fileName = createdFileanme(totalVoiceCount)
// create your recording // depending on how you do this, it probably runs on a background thread anyways
}
fun createdFileName(totalVoiceCount : long){
return "untitled"+ String.valueOf(totalVoiceCount)
}
This works reliably because the LiveData has enough time to update the local copy of totalVoiceCount before the user has the chance to click the button.
B) Based on the answer in your parallel question you can of course outsource even more to a background thread. Then you also have the option to call the DAO query with a non-livedata return (as room returns non-livedata queries only on background threads). Is it worth to implement the threading suggestion of Ridcully? Not possible to answer without knowing what else is going on simultaneously... To me it seems like an overkill, but he is right that the more you do on background threads the better for your refresh rate..
You can return Deferred<Long> from viewModelScope.async. I recommend you to use:
val deferred = viewModelScope.async(Dispatchers.IO) {
return#async mDBVoiceRepository.getTotalOfVoice()
}
val value = deferred.await()
await() is suspend
Edit:
If you want to get a getter which will use in your activity or fragment
you need to write a suspend function like this:
suspend fun getTotalOfVoice(): Long {
return viewModelScope.async(Dispatchers.IO) {
return#async mDBVoiceRepository.getTotalOfVoice()
}.await()
}
But mvvm pattern allows you to create LiveData inside your ViewModel, which gives your fragment an observer.
In view model:
private val _totalOfVoiceLD: MutableLiveData<Long> = MutableLiveData()
val totalOfVoiceLD: LiveData<Long>
get() = _totalOfVoiceLD
fun updateTotalOfVoice() {
viewModelScope.launch(Dispatchers.IO) {
val totalOfVoice = mDBVoiceRepository.getTotalOfVoice()
_totalOfVoiceLD.postValue(totalOfVoice)
}
}
and in your fragment:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.totalOfVoiceLD.observe(viewLifecycleOwner, Observer { totalOfVoice ->
totalOfVoiceTextView.text = totalOfVoice.toString()
})
}
You can use coroutineContext.async to get data from DB and wait for getting it's response with data by using .await function for a async dispatch.
suspend fun getAllVoices() : Long{
val awatingResults = viewModelScope.async(Dispatchers.IO) {
mDBVoiceRepository.getTotalOfVoice()
}
val records = awatingResults.await()
return records
}
It is necessary to call a Suspend function from a coroutine and
async.await() is always called in a suspended function so,
val voiceLiveData: MutableLiveData<Long> = MutableLiveData()
fun getAllVoicesFromDB() {
viewModelScope.launch(Dispatchers.IO) {
voiceLiveData.postValue(mDBVoiceRepository.getTotalOfVoice())
}
}
Now call it where ever you want to get your voice data from database and also remember do your further work inside your voiceLiveData observer where you get your response of voices :)
Live data is designed to be lazy, when the value of the live data changes internally it emits and wherever you are observing it, the onChange function will be invoked. It is designed to fire and forget.
Because room uses background thread to run the query.
You can't expect live data to behave like sharedpreference where you store key value pair.
If you want to achieve something like that.
I would suggest you to use
Paper Db or Realm.
If you need your Room result synchronously, your code should be execute in IO thread. In case of coroutines, you can use Dispatchers.IO. Your code can be changed to this to pass the error.
class HomeViewModel(val mApplication: Application, private val mDBVoiceRepository: DBVoiceRepository) : AndroidViewModel(mApplication) {
fun getTotalOfVoice():Long {
viewModelScope.launch(Dispatchers.IO) { // here
return mDBVoiceRepository.getTotalOfVoice()
}
}
}
If you must run the queries in the main thread, then:
Allow android room to execute queries in main thread.
val dbInstance = Room
.databaseBuilder(ctx, YourDBClass::class.java, "YourDBName")
.allowMainThreadQueries()
.build()
Define the dao method as follows
#Dao
interface DBVoiceDao{
#Query("SELECT count(id) FROM voice_table")
fun getTotalOfVoice(): Long
}
Access the method in the repository
fun getTotalOfVoice():Long {
return dao.getTotalOfVoice()
}
What I'm trying to do
I have an app that's using Room with Coroutines to save search queries in the database. It's also possible to add search suggestions and later on I retrieve this data to show them on a list. I've also made it possible to "pin" some of those suggestions.
My data structure is something like this:
#Entity(
tableName = "SEARCH_HISTORY",
indices = [Index(value = ["text"], unique = true)]
)
data class Suggestion(
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "suggestion_id")
val suggestionId: Long = 0L,
val text: String,
val type: SuggestionType,
#ColumnInfo(name = "insert_date")
val insertDate: Calendar
)
enum class SuggestionType(val value: Int) {
PINNED(0), HISTORY(1), SUGGESTION(2)
}
I have made the "text" field unique to avoid repeated suggestions with different states/types. E.g.: A suggestion that's a pinned item and a previously queried text.
My Coroutine setup looks like this:
private val parentJob: Job = Job()
private val IO: CoroutineContext
get() = parentJob + Dispatchers.IO
private val MAIN: CoroutineContext
get() = parentJob + Dispatchers.Main
private val COMPUTATION: CoroutineContext
get() = parentJob + Dispatchers.Default
And my DAOs are basically like this:
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(obj: Suggestion): Long
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(objList: List<Suggestion>): List<Long>
I also have the following public functions to insert the data into the database:
fun saveQueryToDb(query: String, insertDate: Calendar) {
if (query.isBlank()) {
return
}
val suggestion = Suggestion(
text = query,
insertDate = insertDate,
type = SuggestionType.HISTORY
)
CoroutineScope(IO).launch {
suggestionDAO.insert(suggestion)
}
}
fun addPin(pin: String) {
if (pin.isBlank()) {
return
}
val suggestion = Suggestion(
text = pin,
insertDate = Calendar.getInstance(),
type = SuggestionType.PINNED
)
CoroutineScope(IO).launch {
suggestionDAO.insert(suggestion)
}
}
fun addSuggestions(suggestions: List<String>) {
addItems(suggestions, SuggestionType.SUGGESTION)
}
private fun addItems(items: List<String>, suggestionType: SuggestionType) {
if (items.isEmpty()) {
return
}
CoroutineScope(COMPUTATION).launch {
val insertDate = Calendar.getInstance()
val filteredList = items.filterNot { it.isBlank() }
val suggestionList = filteredList.map { History(text = it, insertDate = insertDate, suggestionType = suggestionType) }
withContext(IO) {
suggestionDAO.insert(suggestionList)
}
}
}
There are also some other methods, but let's focus on the ones above.
EDIT: All of the methods above are part of a lib that I made, they're are not made suspend because I don't want to force a particular type of programming to the user, like forcing to use Rx or Coroutines when using the lib.
The problem
Let's say I try to add a list of suggestions using the addSuggestions() method stated above, and that I also try to add a pinned suggestion using the addPin() method. The pinned text is also present in the suggestion list.
val list = getSuggestions() // Getting a list somewhere
addSuggestions(list)
addPin(list.first())
When I try to do this, sometimes the pin is added first and then it's overwritten by the suggestion present in the list, which makes me think I might've been dealing with some sort of race condition. Since the addSuggestions() method has more data to handle, and both methods will run in parallel, I believe the addPin() method is completing first.
Now, my Coroutines knowledge is pretty limited and I'd like to know if there's a way to enqueue those method calls and make sure they'll execute in the exact same order I invoked them, that must be strongly guaranteed to avoid overriding data and getting funky results later on. How can I achieve such behavior?
I'd follow the Go language slogan "Don't communicate by sharing memory; share memory by communicating", that means instead of maintaining atomic variables or jobs and trying to synchronize between them, model your operations as messages and use Coroutines actors to handle them.
sealed class Message {
data AddSuggestions(val suggestions: List<String>) : Message()
data AddPin(val pin: String) : Message()
}
And in your class
private val parentScope = CoroutineScope(Job())
private val actor = parentScope.actor<Message>(Dispatchers.IO) {
for (msg in channel) {
when (msg) {
is Message.AddSuggestions -> TODO("Map to the Suggestion and do suggestionDAO.insert(suggestions)")
is Message.AddPin -> TODO("Map to the Pin and do suggestionDAO.insert(pin)")
}
}
}
fun addSuggestions(suggestions: List<String>) {
actor.offer(Message.AddSuggestions(suggestions))
}
fun addPin(pin: String) {
actor.offer(Message.AddPin(pin))
}
By using actors you'll be able to queue messages and they will be processed in FIFO order.
By default when you call .launch{}, it launches a new coroutine without blocking the current thread and returns a reference to the coroutine as a Job. The coroutine is canceled when the resulting job is canceled.
It doesn't care or wait for other parts of your code it just runs.
But you can pass a parameter to basically tell it to run immediately or wait for other Coroutine to finish(LAZY).
For Example:
val work_1 = CoroutineScope(IO).launch( start = CoroutineStart.LAZY ){
//do dome work
}
val work_2 = CoroutineScope(IO).launch( start = CoroutineStart.LAZY ){
//do dome work
work_1.join()
}
val work_3 = CoroutineScope(IO).launch( ) {
//do dome work
work_2.join()
}
When you execute the above code first work_3 will finish and invoke work_2 when inturn invoke Work_1 and so on,
The summary of coroutine start options is:
DEFAULT -- immediately schedules coroutine for execution according to its context
LAZY -- starts coroutine lazily, only when it is needed
ATOMIC -- atomically (in a non-cancellable way) schedules coroutine for execution according to its context
UNDISPATCHED -- immediately executes coroutine until its first suspension point in the current thread.
So by default when you call .launch{} start = CoroutineStart.DEFAULT is passed because it is default parameter.
Don't launch coroutines from your database or repository. Use suspending functions and then switch dispatchers like:
suspend fun addPin(pin: String) {
...
withContext(Dispatchers.IO) {
suggestionDAO.insert(suggestion)
}
}
Then from your ViewModel (or Activity/Fragment) make the call:
fun addSuggestionsAndPinFirst(suggestions: List<Suggestion>) {
myCoroutineScope.launch {
repository.addSuggestions(suggestions)
repository.addPin(suggestions.first())
}
}
Why do you have a separate addPin() function anyways? You can just modify a suggestion and then store it:
fun pinAndStoreSuggestion(suggestion: Suggestion) {
myCoroutineScope.launch {
repository.storeSuggestion(suggestion.copy(type = SuggestionType.PINNED)
}
}
Also be careful using a Job like that. If any coroutine fails all your coroutines will be cancelled. Use a SupervisorJob instead. Read more on that here.
Disclaimer: I do not approve of the solution below. I'd rather use an old-fashioned ExecutorService and submit() my Runnable's
So if you really want to synchronize your coroutines in a way that the first function called is also the first one to write to your database. (I'm not sure it is guaranteed since your DAO functions are also suspending and Room uses it's own threads too). Try something like the following unit test:
class TestCoroutineSynchronization {
private val jobId = AtomicInteger(0)
private val jobToRun = AtomicInteger(0)
private val jobMap = mutableMapOf<Int, () -> Unit>()
#Test
fun testCoroutines() = runBlocking {
first()
second()
delay(2000) // delay so our coroutines finish
}
private fun first() {
val jobId = jobId.getAndIncrement()
CoroutineScope(SupervisorJob() + Dispatchers.Default).launch {
delay(1000) // intentionally delay your first coroutine
withContext(Dispatchers.IO) {
submitAndTryRunNextJob(jobId) { println(1) }
}
}
}
private fun second() {
val jobId = jobId.getAndIncrement()
CoroutineScope(SupervisorJob()).launch(Dispatchers.IO) {
submitAndTryRunNextJob(jobId) { println(2) }
}
}
private fun submitAndTryRunNextJob(jobId: Int, action: () -> Unit) {
synchronized(jobMap) {
jobMap[jobId] = action
tryRunNextJob()
}
}
private fun tryRunNextJob() {
var action = jobMap.remove(jobToRun.get())
while (action != null) {
action()
action = jobMap.remove(jobToRun.incrementAndGet())
}
}
}
So what I do on each call is increment a value (jobId) that is later used to prioritize what action to run first. Since you are using suspending function you probably need to add that modifier to the action submitted too (e.g. suspend () -> Unit).