I am migrating my multiple activity app to single activity app.
In the activity I am observing a live data from view model. When the observable triggers, I start a payment activity from a third party SDK as shown below.
onCreate() {
viewmodel.orderCreation.observe {
thirdpartysdk.startPaymentWithThisOrder(context)
}
}
onActivityResult() {
// use payment result
}
As I will be using a Composable now,
#Composable
fun PaymentScreen(onOrderCreated: () -> Unit) {
val orderCreation by viewmodel.orderCreation.observeAsState()
// How to use order creation once here to call onOrderCreated here only once as composable is called again and again
}
Here's my suggestion:
In your viewmodel, create a function to reset your orderCreation. And another field + function to store the payment result.
Something like:
fun resetOrderCreation() {
_orderCreation.value = null
}
fun paymentResult(value: SomeType) {
_paymentResult.value = value
}
Now, in your composable, you can do the following:
#Composable
fun PaymentScreen(onOrderCreated: () -> Unit) {
// 1
val orderCreation by viewmodel.orderCreation.observeAsState()
var paymentResult by viewmodel.paymentResult.observeAsState()
// 2
val launcher = rememberLauncherForActivityResult(
PaymentActivityResultContract()
) { result ->
viewModel.paymentResult(result)
}
...
// 3
LaunchedEffect(orderCreation) {
if (orderCreation != null) {
launcher.launch()
viewModel.resetOrderCreation()
}
}
// 4
if (paymentStatus != null) {
// Show some UI showing the payment status
}
}
Explaining the code:
I'm assuming that you're using LiveData. But I really suggest you move to StateFlow instead. See more here.
You will probably need to write a ActivityResultContact to your third party lib. I wrote a post about (it's in Portuguese, but I think you can get the idea translating it to English).
As soon the orderCreation has changed, the LaunchedEffect block will run, then you can start the third party activity using launcher.launch() (the parameters for this call are defined in your ActivityResultContract).
Finally, when the payment status changed, you can show something different to the user.
Related
I'm implementing registration in my application and, after filling in the respective fields, I click on a button that will make a registration request to the API. Meanwhile, I place a Loading View and when I receive the successful response, I execute the navigation to the OnBoarding screen. The issue is that the navController is always running the navigation and doing the navigation and popUp several times, when it should only do it once. I always get this warning on logs: Ignoring popBackStack to destination 29021787 as it was not found on the current back stack and I am not able to do any click or focus in the OnBoardingScreen.
My code:
val uiState by registerViewModel.uiState.collectAsState()
when (uiState) {
is BaseViewState.Data -> {
navController.navigate(NavigationItem.OnBoarding.route) {
popUpTo(NavigationItem.Register.route) {
inclusive = true
}
}
}
is BaseViewState.Loading -> LoadingView()
is BaseViewState.Error -> BannerView()
else -> {}
}
On button click I call the viewModel like this:
registerViewModel.onTriggerEvent(
RegisterEvent.CreateUser(
usernameInputState.value.text,
emailInputState.value.text,
passwordInputState.value.text
)
)
And, in ViewModel, I do my request like this:
override fun onTriggerEvent(eventType: RegisterEvent) {
when (eventType) {
is RegisterEvent.CreateUser -> createUser(eventType.username, eventType.email, eventType.password)
}
}
private fun createUser(username: String, email: String, password: String) = safeLaunch {
setState(BaseViewState.Loading)
execute(createUser(CreateUser.Params(username, email, password))) {
setState(BaseViewState.Data(RegisterViewState(it)))
}
}
I guess it should be caused by recomposition, because I put a breakpoint on first when scenario and it stops here multiple times, but only one on ViewModel. How can I fix this?
This issue is here
is BaseViewState.Data -> {
navController.navigate(NavigationItem.OnBoarding.route) {
popUpTo(NavigationItem.Register.route) {
inclusive = true
}
}
}
Every time you call navController.navigate NavHost will keep on passing through this block, executing an endless loop.
I suggest having the navigate call from a LaunchedEffect with a key (like this),
LaunchedEffect(key1 = "some key") {
navController.navigate(…)
}
or creating a separate structure namely "Events" where they are emitted as SharedFlow and observed via a Unit keyed LaunchedEffect
LaunchedEffect(Unit) {
viewModel.event.collectLatest {
when (it) {
is UiEvent.Navigate -> {
navController.navigate(…)
}
}
}
}
Suppose I have some data that I need to transfer to the UI, and the data should be emitted with a certain delay, so I have a Flow in my ViewModel:
val myFlow = flow {
listOfSomeData.forEachIndexed { index, data ->
//....
emit(data.UIdata)
delay(data.requiredDelay)
}
}
Somewhere in the UI flow is collected and displayed:
#Composable
fun MyUI(viewModel: ViewModel) {
val data by viewModel.myFlow.collectAsState(INITIAL_DATA)
//....
}
Now I want the user to be able to pause/resume emission by pressing some button. How can i do this?
The only thing I could come up with is an infinite loop inside Flow builder:
val pause = mutableStateOf(false)
//....
val myFlow = flow {
listOfSomeData.forEachIndexed { index, data ->
emit(data.UIdata)
delay(data.requiredDelay)
while (pause.value) { delay(100) } //looks ugly
}
}
Is there any other more appropriate way?
You can tidy up your approach by using a flow to hold pause value then collect it:
val pause = MutableStateFlow(false)
//....
val myFlow = flow {
listOfSomeData.forEachIndexed { index, data ->
emit(data.UIdata)
delay(data.requiredDelay)
if (pause.value) pause.first { isPaused -> !isPaused } // suspends
}
}
Do you need mutableStateOf for compose? Maybe you can transform it into a flow but I'm not aware how it looks bc I don't use compose.
A bit of a creative rant below:
I actually was wondering about this and looking for more flexible approach - ideally source flow should suspend during emit. I noticed that it can be done when using buffered flow with BufferOverflow.SUSPEND so I started fiddling with it.
I came up with something like this that lets me suspend any producer:
// assume source flow can't be accessed
val sourceFlow = flow {
listOfSomeData.forEachIndexed { index, data ->
emit(data.UIdata)
delay(data.requiredDelay)
}
}
val pause = MutableStateFlow(false)
val myFlow = sourceFlow
.buffer(Channel.RENDEZVOUS, BufferOverflow.SUSPEND)
.transform {
if (pause.value) pause.first { isPaused -> !isPaused }
emit(it)
}
.buffer()
It does seem like a small hack to me and there's a downside that source flow will still get to the next emit call after pausing so: n value gets suspended inside transform but source gets suspended on n+1.
If anyone has better idea on how to suspend source flow "immediately" I'd be happy to hear it.
If you don't need a specific delay you can use flow.filter{pause.value != true}
I have created a composable called ResolveAuth. ResolveAuth is the first screen when user opens the app after Splash. All it does is check whether an email is present in Datastore or not. If yes redirect to main screen and if not then redirect to tutorial screen
Here is my composable and viewmodel code
#Composable
fun ResolveAuth(resolveAuthViewModel: ResolveAuthViewModel, navController: NavController) {
Scaffold(content = {
ProgressBar()
when {
resolveAuthViewModel.userEmail.value != "" -> {
navController.navigate(Screen.Main.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
resolveAuthViewModel.userEmail.value == "" -> {
navController.navigate(Screen.Tutorial.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
}
})
}
#HiltViewModel
class ResolveAuthViewModel #Inject constructor(
private val dataStoreManager: DataStoreManager): ViewModel(){
val userEmail = MutableLiveData<String>()
init {
viewModelScope.launch{
val job = async {dataStoreManager.email.first()}
val email = job.await()
if(email != ""){
userEmail.value = email
}
}
}
}
But I keep getting an exception saying
java.lang.IllegalStateException: You cannot access the NavBackStackEntry's ViewModels until it is added to the NavController's back stack (i.e., the Lifecycle of the NavBackStackEntry reaches the CREATED state).
I am using below jetpack lib for navigation
implementation("androidx.navigation:navigation-compose:2.4.0-rc01")
There is no issue in my Main and Tutorial screen as I tried to run them separately and it works fine.
Easily resolvable, just add this when call to a Side-Effect instead.
LaunchedEffect(Unit){
while(!isNavStackReady) // Hold execution while the NavStack populates.
delay(16) // Keeps the resources free for other threads.
when {
resolveAuthViewModel.userEmail.value != "" -> {
navController.navigate(Screen.Main.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
resolveAuthViewModel.userEmail.value == "" -> {
navController.navigate(Screen.Tutorial.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
}
}
Here, the call to navigate is made only after the currentBackStackEntry has been completely filled, so it yields no error. The original error occurred since you were calling navigate before the concerned composable was even made available to the nav stack.
As for how to update the isNavStackReady variable to reflect the correct state of the navStack, it is fairly simple. Create the variable at a top-level declaration, such that only the required components may access it. May as well throw it inside a viewModel if you please. Set the default value of the var to false, for obvious reasons. Here's the update mechanism.
#Composable
fun StartDestination(){
isNavStackReady = true
}
That's it, that's really it. If you could successfully navigate to your start destination that you define in the nav graph, it means the navStack has likely been populated well. Hence, you just update this variable here, and the LaunchedEffect block up there will respond to this update, and the while loop that's been holding execution off, will finally break. It will then call the navigate on the appropriate destination route. Remember, however, that the isNavStackReady variable, for this mechanism to work, needs to be a state-holder, i.e., initialised with mutableStateOf(false). Using delegates, of course, is completely fine (personally encouraged).
Now, all this is fine, but actually, it's not quite the right implementation. You see, this entire thing is taken care of completely internally by the navigation APIs for us, but it breaks because we are trying to do its job, and we suck at it.
We are creating an intermediate route to land on, at the start of the app, and from there, immediately navigating to another screen based on calculations. So, all we want is to open the app at a desired page, that is, start the navigator on a desired page when it is first created. We have a handy parameter called startDestination, just for that.
Hence, the ideal, simple, beautiful solution would be to just
startDestination = when {
resolveAuthViewModel.userEmail.value != "" -> {
navController.navigate(Screen.Main.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
resolveAuthViewModel.userEmail.value == "" -> {
navController.navigate(Screen.Tutorial.route) {
popUpTo(0)
}
resolveAuthViewModel.userEmail.value = null
}
}
in your NavBuilder's arguments. Tiniest silliest logical flaw, that so many people couldn't get. It's intriguing to think how the human mind works...
Happy New Year,
Is this good to put the collect latest inside observe?
viewModel.fetchUserProfileLocal(PreferencesManager(requireContext()).userName!!)
.observe(viewLifecycleOwner) {
if (it != null) {
viewLifecycleOwner.lifecycleScope.launch {
viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
launch {
viewModel.referralDetailsResponse.collect { referralResponseState ->
when (referralResponseState) {
State.Empty -> {
}
is State.Failed -> {
Timber.e("${referralResponseState.message}")
}
State.Loading -> {
Timber.i("LOADING")
}
is State.Success<*> -> {
// ACCESS LIVEDATA RESULT HERE??
}}}}
I'm sure it isn't, my API is called thrice too as the local DB changes, what is the right way to do this?
My ViewModel looks like this where I'm getting user information from local Room DB and referral details response is the API response
private val _referralDetailsResponse = Channel<State>(Channel.BUFFERED)
val referralDetailsResponse = _referralDetailsResponse.receiveAsFlow()
init {
val inviteSlug: String? = savedStateHandle["inviteSlug"]
// Fire invite link
if (inviteSlug != null) {
referralDetail(inviteSlug)
}
}
fun referralDetail(referral: String?) = viewModelScope.launch {
_referralDetailsResponse.send(State.Loading)
when (
val response =
groupsRepositoryImpl.referralDetails(referral)
) {
is ResultWrapper.GenericError -> {
_referralDetailsResponse.send(State.Failed(response.error?.error))
}
ResultWrapper.NetworkError -> {
_referralDetailsResponse.send(State.Failed("Network Error"))
}
is ResultWrapper.Success<*> -> {
_referralDetailsResponse.send(State.Success(response.value))
}
}
}
fun fetchUserProfileLocal(username: String) =
userRepository.getUserLocal(username).asLiveData()
You can combine both streams of data into one stream and use their results. For example we can convert LiveData to Flow, using LiveData.asFlow() extension function, and combine both flows:
combine(
viewModel.fetchUserProfileLocal(PreferencesManager(requireContext()).userName!!).asFlow(),
viewModel.referralDetailsResponse
) { userProfile, referralResponseState ->
...
}.launchIn(viewLifecycleOwner.lifecycleScope)
But it is better to move combining logic to ViewModel class and observe the overall result.
Dependency to use LiveData.asFlow() extension function:
implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.4.0"
it certainly is not a good practice to put a collect inside the observe.
I think what you should do is collect your livedata/flows inside your viewmodel and expose the 'state' of your UI from it with different values or a combined state object using either Flows or Livedata
for example in your first code block I would change it like this
get rid of "userProfile" from your viewmodel
create and expose from your viewmodel to your activity three LiveData/StateFlow objects for your communityFeedPageData, errorMessage, refreshingState
then in your viewmodel, where you would update the "userProfile" update the three new state objects instead
this way you will take the business logic of "what to do in each state" outside from your activity and inside your viewmodel, and your Activity's job will become to only update your UI based on values from your viewmodel
For the specific case of your errorMessage and because you want to show it only once and not re-show it on Activity rotation, consider exposing a hot flow like this:
private val errorMessageChannel = Channel<CharSequence>()
val errorMessageFlow = errorMessageChannel.receiveAsFlow()
What "receiveAsFlow()" does really nicely, is that something emitted to the channel will be collected by one collector only, so a new collector (eg if your activity recreates on a rotation) will not receive the message and your user will not see it again
I am working on a compose screen, where on application open, i redirect user to profile page. And if profile is complete, then redirect to user list page.
my code is like below
#Composable
fun UserProfile(navigateToProviderList: () -> Unit) {
val viewModel: MainActivityViewModel = viewModel()
if(viewModel.userProfileComplete == true) {
navigateToProviderList()
return
}
else {
//compose elements here
}
}
but the app is blinking and when logged, i can see its calling the above redirect condition again and again. when going through doc, its mentioned that we should navigate only through callbacks. How do i handle this condition here? i don't have onCLick condition here.
Content of composable function can be called many times.
If you need to do some action inside composable, you need to use side effects
In this case LaunchedEffect should work:
LaunchedEffect(viewModel.userProfileComplete == true) {
if(viewModel.userProfileComplete == true) {
navigateToProviderList()
}
}
In the key(first argument of LaunchedEffect) you need to specify some key. Each time this key changes since the last recomposition, the inner code will be called. You may put Unit there, in this case it'll only be called once, when the view appears at the first place
The LaunchedEffect did not work for me since I wanted to use it in UI thread but it wasn't for some reason :/
However, I made this for my self:
#Composable
fun <T> SelfDestructEvent(liveData: LiveData<T>, onEvent: (argument: T) -> Unit) {
val previousState = remember { mutableStateOf(false) }
val state by liveData.observeAsState(null)
if (state != null && !previousState.value) {
previousState.value = true
onEvent.invoke(state!!)
}
}
and you use it like this in any other composables:
SingleEvent(viewModel.someLiveData) {
//your action with that data, whenever it was triggered, but only once
}