I have a composable function named 'Page' as a basic composable to hold NavHost for my app, please see architecture below:
#Composable
fun Page(viewModel: LdvToolViewModel = hiltViewModel(), scaffoldState: ScaffoldState, navController: NavHostController){
val statusBarMode = viewModel.statusBarUiState
val uiController = rememberSystemUiController()
LaunchedEffect(statusBarMode){
uiController.run {
if(statusBarMode.isDarkContent){
setStatusBarColor(color = Color.White, darkIcons = true)
}else{
setStatusBarColor(color = LdvOrange, darkIcons = false)
}
}
}
val navBuilder: NavGraphBuilder.() -> Unit = {
composable(LdvPages.SEARCHING.name) { SearchUi(viewModel, scaffoldState = scaffoldState) }
composable(LdvPages.ERROR.name) { ErrorUi(viewModel,scaffoldState = scaffoldState) }
composable(LdvPages.PANEL.name) { PanelUi(scaffoldState,viewModel, mBaseViewModel) }
composable(LdvPages.PrivacyPolicy.name){ PrivacyPolicy(scaffoldState)}
composable(LdvPages.TermsOfUse.name){ TermsOfUse(scaffoldState)}
composable(LdvPages.OpenSourceLicense.name){ OpenSourceLicense(scaffoldState)}
composable(LdvPages.DebugPage.name){ DebugPage(viewModel)}
}
val start by derivedStateOf {
if (...){
LdvPages.PANEL.name }else if(...){
LdvPages.ERROR.name
}else{LdvPages.SEARCHING.name}
}
NavHost(navController = navController, startDestination = start, builder = navBuilder)
if(!isNfcEnable){
viewModel.setNfcDisableContent()
ErrorDialog(viewModel = viewModel){
startActivity(Intent(Settings.ACTION_NFC_SETTINGS));
}
}
}
As you can see that 'LdvToolViewModel' has been injected to 'Page' as hiltViewModel. To keep 'LdvToolViewModel' as one instance among lifecycles of nested-composable functions in navBuilder, I have to pass it as parameter to those functions. Is there any better way like I can somehow inject 'LdvToolViewModel' in those functions as hiltViewModel and meanwhile I can still have the injected hiltViewModel as a same instance?
Imagine you have a "HomeGraph", with "Home" as a parent destination, and few destination screens that should share the same ViewModel instance.
First get a NavBackStackEntry, by passing your parent route
val parentEntry: NavBackStackEntry = remember(navBackStackEntry) {
navController.getBackStackEntry(Destination.HomeGraph.route)
}
Then get an instance of a ViewModel by passing the parent NavBackStackEntry
val userViewModel = hiltViewModel<HomeViewModel>(parentEntry)
Also, remember that if you navigate to Destination.HomeGraph.route either from nested navigation or from a different graph a new instance of ViewModel will be created, so if you navigate within a single graph, navigate to startDestination e.g Destination.Home.route - this way you will keep the same ViewModel instance.
I don't thing we have a well-defined ViewModel sharing in compose as we had with a view system e.g by activityViewModels(), but keeping ViewModel state in graphs while user is not accessing them is a bad practice.
You can always pass the ViewModel in one of the graph extension function if necessary.
fun NavGraphBuilder.homeGraph(navController: NavHostController) {
navigation(
startDestination = Destination.Home.route,
route = Destination.HomeGraph.route
) {
composable(Destination.Home.route) { navBackStackEntry ->
val parentEntry = remember(navBackStackEntry) {
navController.getBackStackEntry(Destination.HomeGraph.route)
}
val homeViewModel = hiltViewModel<HomeViewModel>(parentEntry)
HomeRoute(
viewModel = homeViewModel,
onNavigate = { dest ->
navController.navigate(dest.route)
})
}
composable(Destination.Search.route) { navBackStackEntry ->
val parentEntry = remember(navBackStackEntry) {
navController.getBackStackEntry(Destination.HomeGraph.route)
}
val homeViewModel = hiltViewModel<HomeViewModel>(parentEntry)
UserSupportRoute(
viewModel = userViewModel,
onNavigate = { dest ->
navController.navigate(dest.route) {
popUpTo(Destination.Search.route) {
inclusive = true
}
}
})
}
}
Related
I have a function like:
#Composable
fun LazyElementList(data: Flow<PagingData<Element>>) {
val scrollState = rememberLazyListState()
val elements = data.collectAsLazyPagingItems()
LazyColumn(state = scrollState) {
items(elements) {
DisplayElement(it)
}
}
}
I would like when navigating to another screen and back to maintain the place in the list.
Unexpectedly, the value of scrollState is maintained when visiting child screens. If it wasn't, it should be hoisted, probably into the ViewModel.
In the code in the question scrollState will be reset to the beginning of the list because there are no items in the list on the first composition. You need to wait to display the list until the elements are loaded.
#Composable
fun LazyElementList(data: Flow<PagingData<Element>>) {
val scrollState = rememberLazyListState()
val elements = data.collectAsLazyPagingItems()
if (elements.isLoading) {
DisplayLoadingMessage()
} else {
LazyColumn(state = scrollState) {
items(elements) {
DisplayElement(it)
}
}
}
}
fun LazyPagingItems.isLoading(): Boolean
get() = loadState.refresh is LoadState.Loading
Folks I am stuck engineering a proper solution to access a viewModel scoped to a nav graph , from a button that exists in the TopAppBar in a compose application
Scaffold{
TopAppBar-> Contains the Save Button
Body->
BioDataGraph() -> Contains 5 screens to gather biodata information , and a viewmodel scoped to the graph
}
}
My BioDataViewModel looks like this
class BioDataViewModel{
fun gatherPersonalInformation()
fun gatherPhotos()
...
fun onSaveEverything()
}
The issue i came across is as i described above , how should i go about access the BioDataViewModel , such that i can invoke onSaveEverything when save is clicked in the TopAppBar.
What I have tried
private val performSave by mutableStateOf(false)
Scaffold(
topBar = {
TopAppBar(currentDestination){
//save is clicked.
performSave = true
}
})
{
NavHost(
navController = navController,
startDestination = homeNavigationRoute,
modifier = Modifier
.padding(padding)
.consumedWindowInsets(padding),
) {
composable(route = bioDataRoute) {
val viewModel = hiltViewModel<BioDataViewModel>()
if (performSave){
viewModel.onSaveEverything()
}
BioDataScreen(
viewModel
)
}
}
}
The problem with the approach above is that how and when should i reset the state of performSave ? . Because if i do not set it to false; on every recomposition onSaveEverything would get called.
What would be the best way to engineer a solution for this ? . I checked to see if a similar situation was tackled in jetpack samples , but i found nothing there .
I'm not sure if I understand you correctly, but you can define the BioDataViewModel in activity level, and you can access it in the TopAppBar like this
class MyActivity: ComponentActivity() {
// BioDataViewModel definition here
private val viewModel: BioDataViewModel by viewModels()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
Scaffold(
topBar = {
TopAppBar(currentDestination) {
//save is clicked.
viewModel.onSaveEverything() // call onSaveEverything here
}
})
{
...
...
}
...
...
Edit:
If you want to have the same instance of ViewModel from activity and NavGraph level, you can consider this, a reference from my other answer.
You can define the ViewModelStoreOwner in the navigation graph level.
NavHost(
navController = navController,
startDestination = homeNavigationRoute,
modifier = Modifier
.padding(padding)
.consumedWindowInsets(padding),
) {
val viewModelStoreOwner = checkNotNull(LocalViewModelStoreOwner.current) {
"LocalViewModelStoreOwner not available"
}
composable(route = bioDataRoute) {
val viewModel = hiltViewModel<BioDataViewModel>(viewModelStoreOwner)
if (performSave){
viewModel.onSaveEverything()
}
BioDataScreen(
viewModel
)
}
}
I am quite new in Android Flow and JetPack compose,
I am trying to update my UI when mutable state is being changed , but this is not calling our composable , here is my code
#Composable
fun Grid() {
val mainViewModel by viewModels<DashBoardViewModel>()
mainViewModel.getData()
when (val result = mainViewModel.mutableState.value) {
is Resource.Success -> {
LazyVerticalGrid(
cells = GridCells.Adaptive(100.dp)
) {
items(result.device.items.first().devices.count()) {
EachItem(it)
}
}
}
is Resource.Error -> { Text(text = result.message) }
Resource.Loading -> { CircularProgressIndicator() }
Resource.Empty -> {}
else -> { CircularProgressIndicator() }
}
}
ViewModel:
#HiltViewModel
class DashBoardViewModel #Inject constructor(
private val dashBoardRepository: DashBoardRepository
) : ViewModel() {
val mutableState = MutableLiveData<Resource>()
fun getData() = viewModelScope.launch {
flow {
emit(Resource.Loading)
try {
val mResponse = dashBoardRepository.getDevice()
emit(Resource.Success(mResponse))
} catch (e: Exception) {
e.printStackTrace()
emit(Resource.Error("Error"))
}
}.flowOn(Dispatchers.IO).collect {
mutableState.value = it
}
}
}
There are two problems in your code:
mainViewModel.mutableState.value gets only the current value from your mutable state. Your composable will not be notified when this value changes and thus it cannot reflect the change. If you want to use LiveData in your viewmodel, you have to use observeAsState() extension function which converts LivaData to State that can be automatically observed by composable function. Other option is to have (Mutable)State directly in your viewmodel. See this state explanation.
Your mainViewModel.getData() function will be called every time your Grid() function recomposes, which will be every time your mainViewModel.mutableState changes (once you observe it correctly). You definitely don't want that. Better solution would be to call getData() from your viewModel's init block, or, if you really need to call it from your composable function, use LaunchedEffect.
And, as a side note, the way you are creating flow and then collecting it into LiveData is really odd and unnecessary. You can do something like this instead:
fun getData() = viewModelScope.launch {
mutableState.value = Resource.Loading
try {
val mResponse = dashBoardRepository.getDevice()
mutableState.value = Resource.Success(mResponse)
} catch (e: Exception) {
e.printStackTrace()
mutableState.value = Resource.Error("Error")
}
}
I try to display live data in an MPAndroidChart hosted in an AndroidView.
I get the graph but an UnsupportedOperationException happens when I call addEntry() to update the graph dynamically. Am I doing something wrong?
You find a demo repo in the comments.
#Composable
fun MyLineChart() {
val mainViewModel = viewModel()
val sensorData = mainViewModel.sensorFlow.collectAsState(SensorModel(0F,0F)).value
AndroidView(modifier = Modifier.fillMaxSize(),
factory = { context ->
val lineChart = LineChart(context)
var entries = listOf(Entry(1f,1f))
val dataSet = LineDataSet(entries, "Label").apply { color = Color.Red.toArgb() }
val lineData = LineData(dataSet)
lineChart.data = lineData
lineChart.invalidate()
lineChart
}){
try {
Log.d("TAG", "MyLineChart: Update --- Current thread id: ${Thread.currentThread()}")
it.data.dataSets[0].addEntry(Entry(sensorData.x, sensorData.y))
it.lineData.notifyDataChanged()
it.notifyDataSetChanged()
it.invalidate()
} catch(ex: Exception) {
Log.d("TAG", "MyLineChart: $ex")
}
}
}
The data is sent to the view via the following ViewModel:
#HiltViewModel
class MainViewModel #Inject constructor(#ApplicationContext var appContext: Context) : ViewModel() {
private var rand: Random = Random(1)
val sensorFlow: Flow<SensorModel> = flow<SensorModel> {
while (true) {
delay(1000L)
Log.d("TAG", "sensorFlow: Current thread id: ${Thread.currentThread()}")
emit(SensorModel(rand.nextFloat(), rand.nextFloat()))
}
}
}
You pass entries to LineDataSet, which is an immutable list.
This library seems to have a pretty bad API, because it doesn't ask for a modifiable list as a parameter, but at the same time it doesn't make it modifiable on its side. This causes you to try to modify the immutable list, which leads to an exception.
Replace
var entries = listOf(Entry(1f,1f))
with
val entries = mutableListOf(Entry(1f,1f))
p.s. I can't advise you another graph library as I haven't worked with any, but I would advise you to look for a library with a better API.
try this code:
// it.data.dataSets[0].addEntry(Entry(sensorData.x, sensorData.y))
val entryList = mutableListOf<Entry>()
entryList.add(Entry(sensorData.x, sensorData.y))
val dataSet = LineDataSet(entryList, "Label").apply {
color = Color.Red.toArgb()
}
it.data = LineData(dataSet)
Consider this example.
For authentication, we'll be using 2 screens - one screen to enter phone number and the other to enter OTP.
Both these screens were made in Jetpack Compose and the for the NavGraph, we are using compose navigation.
Also I have to mention that DI is being handled by Koin.
val navController = rememberNavController()
NavHost(navController) {
navigation(
startDestination = "phone_number_screen",
route = "auth"
) {
composable(route = "phone_number_screen") {
// Get's a new instance of AuthViewModel
PhoneNumberScreen(viewModel = getViewModel<AuthViewModel>())
}
composable(route = "otp_screen") {
// Get's a new instance of AuthViewModel
OTPScreen(viewModel = getViewModel<AuthViewModel>())
}
}
}
So how can we share the same viewmodel among two or more composables in a Jetpack compose NavGraph?
You can to pass your top viewModelStoreOwner to each destination
directly passing to .viewModel() call, composable("first") in my example
overriding LocalViewModelStoreOwner for the whole content, so each composable inside CompositionLocalProvider will have access to the same view models, composable("second") in my example
val viewModelStoreOwner = checkNotNull(LocalViewModelStoreOwner.current) {
"No ViewModelStoreOwner was provided via LocalViewModelStoreOwner"
}
val navController = rememberNavController()
NavHost(navController = navController, startDestination = "first") {
composable("first") {
val model = viewModel<SharedModel>(viewModelStoreOwner = viewModelStoreOwner)
}
composable("second") {
CompositionLocalProvider(
LocalViewModelStoreOwner provides viewModelStoreOwner
) {
SecondScreen()
}
}
}
In the second case, you can get your model at any level of the composition tree, which is inside the CompositionLocalProvider:
#Composable
fun SecondScreen() {
val model = viewModel<SharedModel>()
SomeView()
}
#Composable
fun SomeView() {
val model = viewModel<SharedModel>()
}
Using Hilt you could do something like the below. But since you are using Koin I don't know the way of Koin yet.
#Composable
fun MyApp() {
NavHost(navController, startDestination = startRoute) {
navigation(startDestination = innerStartRoute, route = "Parent") {
// ...
composable("exampleWithRoute") { backStackEntry ->
val parentEntry = remember {
navController.getBackStackEntry("Parent")
}
val parentViewModel = hiltViewModel<ParentViewModel>(
parentEntry
)
ExampleWithRouteScreen(parentViewModel)
}
}
}
}
Official doc: https://developer.android.com/jetpack/compose/libraries#hilt
Here is an other way with Koin.
It strictly do the same than the validated answer but simpler to write. It will have exactly the same viewModelStoreOwner without having to write it explicitly. Please tell me if i'm wrong.
val navController = rememberNavController()
val sharedViewModel = getViewModel()
NavHost(navController = navController, startDestination = "first") {
composable("first") {
// You can use sharedViewModel
}
composable("second") {
// You can use sharedViewModel
}
}