I am trying to save the HorizontalPager currentPage state in the room database, so was thinking when the composable closes I will save the currentPage value to the database. I did it like this.
DisposableEffect(true) {
(context as? Activity)?.window?.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
onDispose {
scope.launch(Dispatchers.IO) {
vm.updateBookProgress(vm.book.bookId, pagerState.currentPage+1)
}
(context as? Activity)?.window?.clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
}
}
but the data is not stored in the database, I am guessing that the composable was disposed of so the coroutine was cancelled? I am not sure.
I guess you are true, the coroutine will get cancelled.
I suggest you have a globalViewModel or a progressViewModel initiated in the parent compose, pass it in your current compose and update your progress.
if you are not using ViewModel, you can pass a lambda to your compose from your parent composable and update progress in lambda.
example:
#Composable
fun HorizontalPager(onProgress: (bookId: Int, progress: Int) -> Unit){
DisposableEffect(true) {
(context as? Activity)?.window?.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
onDispose {
onProgress(20, 10)
(context as? Activity)?.window?.clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
}
}
}
Related
I have a StateFlow from which my List composable collects any changes as a State.
private val _people = MutableStateFlow(personDataList())
val people = _people.asStateFlow()
And inside my viewModel, I perform modifications on _people and I verify that people as a read-only StateFlow is also getting updated. I also have to make a copy of the original _people as an ordinary kotlin map to use for some verifications use-cases.
val copyAsMap : StateFlow<MutableMap<Int, Person>> = people.map {
it.associateBy( { it.id }, { it } )
.toMutableMap()
}.stateIn(viewModelScope, SharingStarted.Eagerly, mutableMapOf())
however, with my attempt above, it (the copyAsMap) doesn't get updated when I try to modify the list (e.g delete) an item from the _people StateFlow
Any ideas..? Thanks!
Edit:
Nothing is collecting from the copyAsMap, I just display the values everytime an object is removed from _person state flow
delete function (triggered by an action somewhere)
private fun delete(personModel: Person) {
_person.update { list ->
list.toMutableStateList().apply {
removeIf { it.id == personModel.id }
}
}
copyAsMap.values.forEach {
Log.e("MapCopy", "$it")
}
}
So based on your comment how you delete the item, that's the problem:
_people.update { list ->
list.removeIf { it.id == person.id }
list
}
You get an instance of MutableList here, do the modification and you "update" the flow with the same instance. And, as StateFlow documentation says:
Values in state flow are conflated using Any.equals comparison in a similar way to distinctUntilChanged operator. It is used to conflate incoming updates to value in MutableStateFlow and to suppress emission of the values to collectors when new value is equal to the previously emitted one.
Which means that your updated list is actually never emitted, because it is equal to the previous value.
You have to do something like this:
_people.update { list ->
list.toMutableList().apply { removeIf { ... } }
}
Also, you should define your state as val _people: MutableStateFlow<List<T>> = .... This would prevent some mistakes you can make.
I want to load data from Firestore, and combine it with other data using Flow combine()
ViewModel:
private val userCurrentProject = MutableStateFlow("")
val projects = repository
.listenToProject() //listening via Firestore snapshot listener, no problem here
.combine(userCurrentProject) { projects, currentProjectName ->
// combine works and called normally
projects.map { project ->
project.apply {
isUserCurrentProject = name == currentProjectName
}
}
}
fun setCurrentProject(projectName: String) = viewModelScope.launch {
userCurrentProject.emit(projectName)
}
Composables:
fun ProjectListScreen(navController: NavHostController, viewModel: ProjectsViewModel) {
val projects by viewModel.projects.collectAsState(initial = emptyList())
// This is where the problem started
// Lazy column not updated when projects flow is emitting new value
// Even Timber log does not called
Timber.d("Projects : $projects")
LazyColumn {
items(projects) { project ->
ProjectItem(project = project) {
currentlySelectedProject = project
scope.launch { bottomSheetState.show() }
}
}
}
The flow is working normally, but the state never got updated, I don't know why. Maybe this is a problem with collectAsState()?
But the state is updated when I navigate to next screen (add new project screen), then press back (popBackStack)
NB: using asLiveData() with observeAsState() does not work either.
I've finally found the answer
The culprit is that a State of custom object/class behaves differently than a state of primitives (String, Int, etc.)
For a State of object, you need to use copy()
So I just changed this part of ViewModel
val projects = repository
.listenProject()
.combine(userCurrentProject) { projects, currentProjectName ->
projects.map { project ->
// use copy instead of apply
val isCurrentProject = project.name == currentProjectName
project.copy(isUserCurrentProject = isCurrentProject)
}
}
I'm trying to use the Google MLKitTranslate framework for offline translation in my app. I have written a function for downloading a language model.
public func downloadModel(forLanguage language: TranslateLanguage) -> Observable<Double> {
let model = TranslateRemoteModel.translateRemoteModel(language: language)
return Observable<Double>.create { _ -> Disposable in
// Observe the download progress
self.progress = ModelManager.modelManager().download(
model,
conditions: ModelDownloadConditions(
allowsCellularAccess: true,
allowsBackgroundDownloading: true
)
)
return Disposables.create()
}
}
progress here has the Progress type.
However I want to create an Observable that sends out a .next event when I have an update in the .fractionComplete and a .completed event when .fractionComplete is 1.0.
I have tried using .rx.observe and .rx.observeWeakly (KVO) on the progress object but it didn't work.
So how can I create an observable from this Progress event? Help is much appreciated.
This should work:
func downloadModel(forLanguage language: TranslateLanguage) -> Observable<Double> {
let model = TranslateRemoteModel.translateRemoteModel(language: language)
return Observable.create { observer -> Disposable in
let progress = ModelManager.modelManager().download(
model,
conditions: ModelDownloadConditions(
allowsCellularAccess: true,
allowsBackgroundDownloading: true
)
)
return progress.rx.observe(Double.self, "fractionCompleted")
.compactMap { $0 }
.takeUntil(.inclusive, predicate: { $0 >= 1.0 })
.subscribe(observer)
}
}
A couple of things to note. This is not a method, do not put it in a class. It is a free function. The progress object does not need to be retained by any class, the model manager will retain it and release it when it isn't needed anymore.
If you are using the create(_:) operator, do not ignore the parameter being passed into your closure. If you do that you will not be able to emit anything.
just trying to implement SwiftUI and Combine in my new project.
But stuck in this:
func task() -> AnyPublisher<Int, Error> {
return AnyPublisher { subscriber in
subscriber.receive(Int(arc4random()))
subscriber.receive(completion: .finished)
}
}
This produces the following compiler error:
Type '(_) -> ()' does not conform to protocol 'Publisher'
Why?
Update
Actually Random here is just as an example. The real code will look like this:
func task() -> AnyPublisher<SomeCodableModel, Error> {
return AnyPublisher { subscriber in
BackendCall.MakeApiCallWithCompletionHandler { response, error in
if let error == error {
subscriber.receive(.failure(error))
} else {
subscriber.receive(.success(response.data.filter))
subscriber.receive(.finished)
}
}
}
}
Unfortunately, I don't have access to BackendCall API since it is private.
It's kind of pseudocode but, it pretty close to the real one.
You cannot initialise an AnyPublisher with a closure accepting a Subscriber. You can only initialise an AnyPublisher from a Publisher. If you want to create a custom Publisher that emits a single random Int as soon as it receives a subscriber and then completes, you can create a custom type conforming to Publisher and in the required method, receive(subscriber:), do exactly what you were doing in your closure.
struct RandomNumberPublisher: Publisher {
typealias Output = Int
typealias Failure = Never
func receive<S>(subscriber: S) where S : Subscriber, Failure == S.Failure, Output == S.Input {
subscriber.receive(Int.random(in: 0...Int.max))
subscriber.receive(completion: .finished)
}
}
Then in your task method, you simply need to create a RandomNumberPublisher and then type erase it.
func task() -> AnyPublisher<Int, Never> {
return RandomNumberPublisher().eraseToAnyPublisher()
}
If all you want is a single random value, use Just
fun task() -> AnyPublisher<Int, Never> {
return Just(Int.random(in: 0...Int.max)).eraseToAnyPublisher()
}
Sidenote: don't use Int(arc4random()) anymore.
You're likely better off wrapping this in a Future publisher, possibly also wrapped with Deferred if you want it to response when subscriptions come in. Future is an excellent way to wrap external async API calls, especially ones that you can't fully control or otherwise easily adapt.
There's an example in Using Combine for "wrapping an async call with a Future to create a one-shot publisher" that looks like it might map quite closely to what you're trying to do.
If you want it to return more than a single value, then you may want to compose something out of PassthoughSubject or CurrentValueSubject that gives you an interface of -> AnyPublisher<YourType, Error> (or whatever you're looking for).
I am trying to achieve something similar in rxswift example project from RxSwift repo. But in my case there are dependent observables. I couldn't find any solution without using binding in viewmodel
Here is the structure of my viewmodel:
First the definitions of input, output and viewmodel
typealias UserListViewModelInput = (
viewAppearAction: Observable<Void>,
deleteAction: Observable<Int>
)
typealias UserListViewModelOutput = Driver<[User]>
typealias UserListViewModel = (UserListViewModelInput, #escaping UserApi) -> UserListViewModelOutput
Then there is actual implementation which doesn't compile.
let userListViewModel: UserListViewModel = { input, loadUsers in
let loadedUserList = input.viewAppearAction
.flatMapLatest { loadUsers().materialize() }
.elements()
.asDriver(onErrorDriveWith: .never())
let userListAfterDelete = input.deleteAction
.withLatestFrom(userList) { index, users in
users.enumerated().compactMap { $0.offset != index ? $0.element : nil }
}
.asDriver(onErrorJustReturn: [])
let userList = Driver.merge([loadedUserList, userListAfterDelete])
return userList
}
Viewmodel has two job. First load the user list. Second is delete a user at index. The final output is the user list which is downloaded with UserApi minus deleted users.
The problem in here in order the define userList I need to define userListAfterDelete. And in order to define userListAfterDelete I need to define userList.
So is there a way to break this cycle without using binding inside view model? Like a placeholder observable or operator that keeps state?
This is a job for a state machine. What you will see in the code below is that there are two actions that can affect the User array. When the view appears, a new array is downloaded, when delete comes in, a particular user is removed.
This is likely the most common pattern seen in reactive code dealing with state. So common that there are whole libraries that implement some variation of it.
let userListViewModel: UserListViewModel = { input, loadUsers in
enum Action {
case reset([User])
case delete(at: Int)
}
let resetUsers = input.viewAppearAction
.flatMapLatest { loadUsers().materialize() }
.compactMap { $0.element }
.map { Action.reset($0) }
let delete = input.deleteAction.map { Action.delete(at: $0) }
return Observable.merge(resetUsers, delete)
.scan(into: [User](), accumulator: { users, action in
switch action {
case let .reset(newUsers):
users = newUsers
case let .delete(index):
users.remove(at: index)
}
})
.asDriver(onErrorJustReturn: [])
}