I have a pretty simple test. I'm waiting for a list of transactions to be received and assigned to a list view.
#Test
fun testTransactionsLoad(){
val listView: ListView? = fragment!!.findView(R.id.listView)
assertNotNull(listView)
await().atMost(20, TimeUnit.SECONDS).until(transactionsLoad(listView!!))
assert(listView.adapter.count > 0)
}
But for some reason, awaitability always send false for this callable:
private fun transactionsLoad(listView: ListView): Callable<Boolean> {
return if (listView.adapter == null){
Callable { false }
} else {
Callable { true }
}
}
It's not the first time Awaitility returns the wrong thing. On my device, the list view loads, proving it should also have an adapter. The adapter still appears as null in the callable though.
Any ideas?
As you are using kotlin, you could do:
await().atMost(20, TimeUnit.SECONDS).until{ listView.adapter != null }
Related
as invers to the question asked here How to convert Flow<List<Object>> to Flow<Object> I want to convert my Flow<Object> to Flow<List<Object>>.
At least I think I want that, so I try to explain what I want to achieve and give some background. I am working on an Android application that uses bluetooth to scan and connect to BLE devices. I'm fairly new to the Android platform and kotlin so I haven't quite grasped all the details despite all the many things I've already learnt.
My repository has a method which returns a Flow of ScanResults from the bluetooth adapter:
fun bluetoothScan(): Flow<ScanResult> {
return bluetoothStack.bluetoothScan()
}
My ViewModel consumes that function, maps the data to my BleScanResult and returns it as LiveData.
val scanResults: LiveData<BleScanResult> =
scanEnabled.flatMapLatest { doScan ->
if (doScan) {
repository.bluetoothScan().map { BleScanResult(it.device.name, it.device.address) }
} else {
emptyFlow()
}
}.asLiveData()
In my activity I want to observer on that data and display it in a RecyclerView:
val adapter = ScanResultListAdapter()
binding.rcBleScanResults.adapter = adapter
viewModel.scanResults.observe(this) { result ->
//result.let { adapter.submitList(it) }
}
The problem is that scanResults is from type Flow<BleScanResult> and not Flow<List<BleScanResult>>, so the call to adapter.submitList(it) throws an error as it is expected to be a list.
So, how do I convert Flow to Flow<List> (with additional filtering of duplicates)? Or is there something I miss about the conception of Flow/LiveData?
You can try to use a MutableList and fill it with the data you get form a Flow, something like the following:
val results: MutableList<BleScanResult> = mutableListOf()
val scanResults: LiveData<List<BleScanResult>> =
scanEnabled.flatMapLatest { doScan ->
if (doScan) {
repository.bluetoothScan().map {
results.apply {
add(BleScanResult(it.device.name, it.device.address))
}
}
} else {
emptyFlow()
}
}.asLiveData()
You can also use a MutableSet instead of MutableList if you want to have a unique list of items (assuming BleScanResult is a data class).
You could use the liveData builder to collect the Flow's values into a MutableList.
Here I copy the MutableList using toList() before emitting it since RecyclerView Adapters don't play well with mutable data sources.
val scanResults: LiveData<List<BleScanResult>> = liveData {
val cumulativeResults = mutableListOf<BleScanResult>()
scanEnabled.flatMapLatest { doScan ->
if (doScan) {
repository.bluetoothScan().map { BleScanResult(it.device.name, it.device.address) }
} else {
emptyFlow()
}
}.collect {
cumulativeResults += it
emit(cumulativeResults.toList())
}
}
If you want to avoid duplicate entries and reordering of entries, you can use a set like this:
val scanResults: LiveData<List<BleScanResult>> = liveData {
val cumulativeResults = mutableSetOf<BleScanResult>()
scanEnabled.flatMapLatest { doScan ->
if (doScan) {
repository.bluetoothScan().map { BleScanResult(it.device.name, it.device.address) }
} else {
emptyFlow()
}
}.collect {
if (it !in cumulativeResults) {
cumulativeResults += it
emit(cumulativeResults.toList())
}
}
}
I'm using Paging 3 with RemoteMediator that shows cached data while fetching new data from the network.
When I refresh my PagingDataAdapter (by calling refresh() on it) I want my RecyclerView to scroll to the top after the refresh is done. In the codelabs they try to handle this via the loadStateFlow the following way:
lifecycleScope.launch {
adapter.loadStateFlow
// Only emit when REFRESH LoadState for RemoteMediator changes.
.distinctUntilChangedBy { it.refresh }
// Only react to cases where Remote REFRESH completes i.e., NotLoading.
.filter { it.refresh is LoadState.NotLoading }
.collect { binding.list.scrollToPosition(0) }
}
This indeed does scroll up, but before DiffUtil has finished. This means that if there is actually new data inserted at the top, the RecyclerView will not scroll all the way up.
I know that RecyclerView adapters have an AdapterDataObserver callback where we can get notified when DiffUtil has finished diffing. But this will cause all kinds of race conditions with PREPEND and APPEND loading states of the adapter which also cause DiffUtil to run (but here we don't want to scroll to the top).
One solution that would work would be to pass PagingData.empty() to the PagingDataAdapter and rerun the same query (just calling refresh won't work because the PagingData is now empty and there is nothing to refresh) but I would prefer to keep my old data visible until I know that refresh actually succeeded.
In cases, such as searching a static content, we can return false inside areItemsTheSame of DiffUtil.ItemCallback as a workaround. I use this also for changing sorting property.
#Florian I can confirm we don't need the postDelayed to scroll to top using version 3.1.0-alpha03 released on 21/07/2021.
Also, I managed to make further filter the loadStateFlow collection so it doesn't prevent StateRestorationPolicy.PREVENT_WHEN_EMPTY to work based on #Alexandr answer. My solution is:
By the time I am writing this, the latest version of Paging3 is 3.1.0-alpha03 so import:
androidx.paging:paging-runtime-ktx:3.1.0-alpha03
Then set the restoration policy of your adapter as following:
adapter.stateRestorationPolicy = RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY
If you have compilation error for the above mentioned change, make sure you are using at least version 1.2.0-alpha02 of RecyclerView. Any version above that is also good:
androidx.recyclerview:recyclerview:1.2.0-alpha02
Then use the filtered loadStateFlow to scroll the list to top only when you refresh the page and items are prepended in the list:
viewLifecycleOwner.lifecycleScope.launch {
challengesAdapter.loadStateFlow
.distinctUntilChanged { old, new ->
old.mediator?.prepend?.endOfPaginationReached.isTrue() ==
new.mediator?.prepend?.endOfPaginationReached.isTrue() }
.filter { it.refresh is LoadState.NotLoading && it.prepend.endOfPaginationReached && !it.append.endOfPaginationReached}
.collect {
mBinding.fragmentChallengesByLocationList.scrollToPosition(0)
}
}
The GitHub discussion can be found here: https://github.com/googlecodelabs/android-paging/issues/149
adapter.refresh()
lifecycleScope.launch {
adapter.loadStateFlow
.collect {
binding.recycleView.smoothScrollToPosition(0)
}
}
Take a look on the code the condition if loadtype is refreshed.
repoDatabase.withTransaction {
// clear all tables in the database
if (loadType == LoadType.REFRESH) {
repoDatabase.remoteKeysDao().clearRemoteKeys()
repoDatabase.reposDao().clearRepos()
}
val prevKey = if (page == GITHUB_STARTING_PAGE_INDEX) null else page - 1
val nextKey = if (endOfPaginationReached) null else page + 1
val keys = repos.map {
Log.e("RemoteKeys", "repoId: ${it.id} prevKey: $prevKey nextKey: $nextKey")
RemoteKeys(repoId = it.id, prevKey = prevKey, nextKey = nextKey)
}
repoDatabase.remoteKeysDao().insertAll(keys)
repoDatabase.reposDao().insertAll(repos)
}
You should delete the condition if LoadType is refresh clear all the tables.
if (loadType == LoadType.REFRESH) {
repoDatabase.remoteKeysDao().clearRemoteKeys()
repoDatabase.reposDao().clearRepos()
}
I've managed the way to improve base code snippet from the topic question.
The key is to listen non-combined variants of properties inside CombinedLoadStates
viewLifecycleOwner.lifecycleScope.launchWhenCreated {
adapter?.loadStateFlow
?.distinctUntilChanged { old, new ->
old.mediator?.prepend?.endOfPaginationReached.isTrue() ==
new.mediator?.prepend?.endOfPaginationReached.isTrue()
}
?.filter { it.refresh is LoadState.NotLoading }
..
// next flow pipeline operators
}
where isTrue is Boolean extension fun
fun Boolean?.isTrue() = this != null && this
So the idea here is to track mediator.prepend:endOfPagination flag states. When mediator has completed his part of paging load for the current page, his prepend state will not change (in case if you are loading pages after scroll down).
Solution works well both in offline & online modes.
If you need to track prepend paging or paging in both directions it is a good starting point to play around with the another CombinedLoadStates properties append,refresh,mediator and source
Follow https://developer.android.com/reference/kotlin/androidx/paging/PagingDataAdapter
val USER_COMPARATOR = object : DiffUtil.ItemCallback<User>() {
override fun areItemsTheSame(oldItem: User, newItem: User): Boolean =
// User ID serves as unique ID
oldItem.userId == newItem.userId
override fun areContentsTheSame(oldItem: User, newItem: User): Boolean =
// Compare full contents (note: Java users should call .equals())
oldItem == newItem
}
class UserAdapter : PagingDataAdapter<User, UserViewHolder>(USER_COMPARATOR) {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): UserViewHolder {
return UserViewHolder.create(parent)
}
override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
val repoItem = getItem(position)
// Note that item may be null, ViewHolder must support binding null item as placeholder
holder.bind(repoItem)
}
}
I am making a network repository that supports multiple data retrieval configs, therefore I want to separate those configs' logic into functions.
However, I have a config that fetches the data continuously at specified intervals. Everything is fine when I emit those values to the original Flow. But when I take the logic into another function and return another Flow through it, it stops caring about its coroutine scope. Even after the scope's cancelation, it keeps on fetching the data.
TLDR: Suspend function returning a flow runs forever when currentCoroutineContext is used to control its loop's termination.
What am I doing wrong here?
Here's the simplified version of my code:
Fragment calling the viewmodels function that basically calls the getData()
lifecycleScope.launch {
viewModel.getLatestDataList()
}
Repository
suspend fun getData(config: MyConfig): Flow<List<Data>>
{
return flow {
when (config)
{
CONTINUOUS ->
{
//It worked fine when fetchContinuously was ingrained to here and emitted directly to the current flow
//And now it keeps on running eternally
fetchContinuously().collect { updatedList ->
emit(updatedList)
}
}
}
}
}
//Note logic of this function is greatly reduced to keep the focus on the problem
private suspend fun fetchContinuously(): Flow<List<Data>>
{
return flow {
while (currentCoroutineContext().isActive)
{
val updatedList = fetchDataListOverNetwork().await()
if (updatedList != null)
{
emit(updatedList)
}
delay(refreshIntervalInMs)
}
Timber.i("Context is no longer active - terminating the continuous-fetch coroutine")
}
}
private suspend fun fetchDataListOverNetwork(): Deferred<List<Data>?> =
withContext(Dispatchers.IO) {
return#withContext async {
var list: List<Data>? = null
try
{
val response = apiService.getDataList().execute()
if (response.isSuccessful && response.body() != null)
{
list = response.body()!!.list
}
else
{
Timber.w("Failed to fetch data from the network database. Error body: ${response.errorBody()}, Response body: ${response.body()}")
}
}
catch (e: Exception)
{
Timber.w("Exception while trying to fetch data from the network database. Stacktrace: ${e.printStackTrace()}")
}
finally
{
return#async list
}
list //IDE is not smart enough to realize we are already returning no matter what inside of the finally block; therefore, this needs to stay here
}
}
I am not sure whether this is a solution to your problem, but you do not need to have a suspending function that returns a Flow. The lambda you are passing is a suspending function itself:
fun <T> flow(block: suspend FlowCollector<T>.() -> Unit): Flow<T> (source)
Here is an example of a flow that repeats a (GraphQl) query (simplified - without type parameters) I am using:
override fun query(query: Query,
updateIntervalMillis: Long): Flow<Result<T>> {
return flow {
// this ensures at least one query
val result: Result<T> = execute(query)
emit(result)
while (coroutineContext[Job]?.isActive == true && updateIntervalMillis > 0) {
delay(updateIntervalMillis)
val otherResult: Result<T> = execute(query)
emit(otherResult)
}
}
}
I'm not that good at Flow but I think the problem is that you are delaying only the getData() flow instead of delaying both of them.
Try adding this:
suspend fun getData(config: MyConfig): Flow<List<Data>>
{
return flow {
when (config)
{
CONTINUOUS ->
{
fetchContinuously().collect { updatedList ->
emit(updatedList)
delay(refreshIntervalInMs)
}
}
}
}
}
Take note of the delay(refreshIntervalInMs).
I have a situation where I need to dispatch an indeterminate number of network calls known only at runtime. Each call returns a list. As each is returned, I need to combine these lists in to a single merged list. I am using coroutines to do this.
The problem I am having relates to the fact that I do not know how many network calls the app will need to make. To address this, I am using a loop to iterate over the list of calls at runtime:
private suspend fun fetchData(params: List<Interval>): List<Item> {
val smallLists = mutableListOf<Deferred<List<Item>>>()
val merged = mutableListOf<List<Item>>()
for (index in 0 until params.size) {
val param = params[index]
// loop stop iterating after this call is dispatched
smallLists[index] = CoroutineScope(Dispatchers.IO).async {
fetchList(param)
}
}
for (index in 0 until smallLists.size) {
merged[index] = smallLists[index].await()
}
return merged.flatMap { it.toList() }
}
private fun fetchList(param: Interval) : List<Item> {
return dataSource.fetchData(param)
}
What happens in this code is that it enters the first loop. The params list is correct. It dispatches the first query, and this query returns (I can see this via a Charles proxy).
But this is where everything just dies. The app does nothing with the network response and the loop terminates (i.e. there is no second iteration of the loop).
I know that everything else is intact because I have an alternate version that does not include looping. It just does two queries, awaits their results, and returns the combined list. It works fine, except that it won't handle a dynamic runtime situation:
private suspend fun fetchData(params: List<Interval>): List<Item> {
val list1 = CoroutineScope(Dispatchers.IO).async {
fetchList(params[0])
}
val list2 = CoroutineScope(Dispatchers.IO).async {
fetchList(params[1])
}
return list1.await() + list2.await()
}
Probably a simple solution here, but I don't see it. Any help is appreciated.
This is not correct:
smallLists[index] = CoroutineScope(Dispatchers.IO).async {
fetchList(param)
}
Your smallLists is empty, so you can't access index index. Change it like this
smallLists.add(CoroutineScope(Dispatchers.IO).async {
fetchList(param)
}
)
Note that you can call awaitAll() on your list of asyncs as well, to simplify your code:
private suspend fun fetchData(params: List<Interval>): List<Item> {
val smallLists = mutableListOf<Deferred<List<Item>>>()
for (index in 0 until params.size) {
val param = params[index]
// loop stop iterating after this call is dispatched
smallLists.add(CoroutineScope(Dispatchers.IO).async {
fetchList(param)
}
})
val merged = smallLists.awaitAll()
return merged.flatMap { it.toList() }
}
I need to implement a search on a large data set that can take some time to complete on mobile devices. So I want to display each matching result as soon as it becomes available.
I need to fetch all available data from a data store that decides whether to get them from network or from the device. This call is an Observable. As soon as the data from that Observable becomes available I want to loop over it, apply a search predicate and notify any Observers for any match found.
So far my idea was to use a PublishSubject to subscribe to and call its onNext function every time the search finds a new match. However I can't seem to get the desired behavior to work.
I'm using MVVM + Android Databinding and want to display every matched entry in a RecyclerView so for every onNext event that is received by the observing viewModel I have to call notifyItemRangeInserted on the RecyclerView's adapter.
class MySearch(val dataStore: MyDataStore) {
private val searchSubject = PublishSubject.create<List<MyDto>>()
fun findEntries(query: String): Observable<List<MyDto>> {
return searchSubject.doOnSubscribe {
// dataStore.fetchAll returns an Observable<List<MyDto>>
dataStore.fetchAll.doOnNext {
myDtos -> if (query.isNotBlank()) {
search(query, myDtos)
} else {
searchSubject.onNext(myDtos)
}
}.subscribe(searchSubject)
}
}
private fun(query: String, data: List<MyDto>) {
data.forEach {
if (it.matches(query)) {
// in real life I cache a few results and don't send each single item
searchSubject.onNext(listOf(it))
}
}
}
fun MyDto.matches(query: String): Boolean // stub
}
-
class MyViewModel(val mySearch: MySearch, val viewNotifications: Observer<Pair<Int, Int>>): BaseObservable() {
var displayItems: List<MyItemViewModel> = listOf()
fun loadData(query: String): Subscription {
return mySearch.findEntries(query)
.observeOn(AndroidSchedulers.mainThread())
.doOnNext(this::onSearchResult)
.doOnCompleted(viewNotifications::onCompleted)
.doOnError(viewNotifications::onError)
.subscribe()
}
private fun onSearchResult(List<MyDto> data) {
val lastIndex = displayItems.lastIndex
displayItems = data.map { createItem(it) }
notifyChange()
viewNotifications.onNext(Pair(lastIndex, data.count()))
}
private fun createItem(dto: MyDto): MyItemViewModel // stub
}
The problem I have with the above code is that with an empty query MyViewModel::onSearchResult is called 3 times in a row and when the query is not empty MyViewModel::onSearchResult isn't called at all.
I suspect the problem lies somewhere in the way I have nested the Observables in findEntries or that I'm subscribing wrong / getting data from a wrong thread.
Does anyone have an idea about this?