I have a LazyColumn that displays a list of shopping list items retrieved from the database in the ViewModel. If the retrieved list of items is empty, the LazyColumn shows the following message: "You don't have any items in this shopping list." The problem is that this message displays briefly for 1 second before the items are displayed. To solve the problem I implemented a circular progress bar while the items are being retrieved, but it does not even appear, and the message is still displayed. How can I fix this?
ViewModel
#HiltViewModel
class ShoppingListScreenViewModel #Inject constructor(
private val getAllShoppingListItemsUseCase: GetAllShoppingListItemsUseCase
) {
private val _shoppingListItemsState = mutableStateOf<Flow<PagingData<ShoppingListItem>>?>(null)
val shoppingListItemsState: State<Flow<PagingData<ShoppingListItem>>?> get() = _shoppingListItemsState
val loading = mutableStateOf(false)
init {
loading.value = true
getAllShoppingListItemsFromDb()
}
private fun getAllShoppingListItemsFromDb() {
viewModelScope.launch {
_shoppingListItemsState.value = getAllShoppingListItemsUseCase().distinctUntilChanged()
loading.value = false
}
}
}
ShoppingListScreen Composable
fun ShoppingListScreen(
navController: NavHostController,
shoppingListScreenViewModel: ShoppingListScreenViewModel,
sharedViewModel: SharedViewModel
) {
val scope = rememberCoroutineScope()
val focusManager = LocalFocusManager.current
val screenHeight = LocalConfiguration.current.screenHeightDp.dp
val allItems = shoppingListScreenViewModel.shoppingListItemsState.value?.collectAsLazyPagingItems()
val showProgressBar = shoppingListScreenViewModel.loading.value
Scaffold(
topBar = {
CustomAppBar(
title = "Shopping List Screen",
titleFontSize = 20.sp,
appBarElevation = 4.dp,
navController = navController
)
},
floatingActionButton = {
FloatingActionButton(
onClick = {
shoppingListScreenViewModel.setStateValue(SHOW_ADD_ITEM_DIALOG_STR, true)
},
backgroundColor = Color.Blue,
contentColor = Color.White
) {
Icon(Icons.Filled.Add, "")
}
},
backgroundColor = Color.White,
// Defaults to false
isFloatingActionButtonDocked = false,
bottomBar = { BottomNavigationBar(navController = navController) }
) {
Box {
LazyColumn(
modifier = Modifier
.fillMaxWidth()
.height(screenHeight)
) {
item {
if (allItems != null && allItems.itemCount == 0) {
Text("You don't have any items in this shopping list.")
}
}
items(
items = allItems!!,
key = { item ->
item.id
}
) { item ->
ShoppingListScreenItem(
navController = navController,
item = item,
sharedViewModel = sharedViewModel
) { isChecked ->
scope.launch {
shoppingListScreenViewModel.changeItemChecked(item!!, isChecked)
}
}
}
item { Spacer(modifier = Modifier.padding(screenHeight - (screenHeight - 70.dp))) }
}
ConditionalCircularProgressBar(isDisplayed = showProgressBar)
}
}
}
Quick solution:
val showProgressBar = shoppingListScreenViewModel.loading.collectAsState() //Use collectAsState, with Flow state in the ViewModel
and add this condition to the "You don't have any items..." if like so:
if (allItems != null && allItems.itemCount == 0 && !showProgressBar) { ... }
The better solution would be to implement this with sealed class(es), where you would return different class for different state (e.g. Loading, Error, Empty, Data). And on the UI side, you just need to when over the possible types of data. Here you can find a perfect example.
I'm using the Paging 3 library with Jetpack Compose and have just implemented swipe to dismiss on some paged data (using the Material library's SwipeToDismiss composable).
Once a swipe action has completed, I call a method in my ViewModel to send an update to the server (either to mark a message as read or to delete a message). Once this action has taken place, I obviously need to refresh the paging data.
My current approach is to have a call back from my ViewModel function which will then handle the refresh on the LazyPagingItems, but this feels wrong.
Is there a better approach?
My ViewModel basically looks like:
#HiltViewModel
class MessageListViewModel #Inject constructor(
private val repository: Repository
): ViewModel() {
companion object {
private const val TAG = "MessageListViewModel"
}
val messages : Flow<PagingData<Message>> = Pager(
PagingConfig(
enablePlaceholders = false,
)
) {
MessagePagingSource(repository)
}.flow.cachedIn(viewModelScope)
fun markRead(guid: String, onComplete: () -> Unit) {
viewModelScope.launch(Dispatchers.IO) {
try {
repository.markMessageRead(guid)
onComplete()
} catch (e: Throwable) {
Log.e(TAG, "Error marking message read: $guid", e)
}
}
}
}
And in my Composable for the message list, it looks a bit like the following:
#Composable
fun MessageListScreen(
vm: MessageListViewModel = viewModel(),
) {
val messages: LazyPagingItems<MessageSummary> = vm.messages.collectAsLazyPagingItems()
val refreshState = rememberSwipeRefreshState(
isRefreshing = messages.loadState.refresh is LoadState.Loading,
)
Scaffold(
topBar = {
SmallTopAppBar (
title = {
Text(stringResource(R.string.message_list_title))
},
)
}
) { paddingValues ->
Box(
modifier = Modifier
.fillMaxSize()
.padding(paddingValues),
) {
SwipeRefresh(
state = refreshState,
onRefresh = {
messages.refresh()
},
) {
LazyColumn(
modifier = Modifier.fillMaxSize(),
horizontalAlignment = Alignment.CenterHorizontally,
verticalArrangement = Arrangement.Top,
) {
items(
items = messages,
key = { it.guid }
) { message ->
message?.let {
MessageRow(
onMarkRead = {
vm.markRead(message.guid) {
messages.refresh()
}
},
)
}
}
}
}
}
}
}
As I say, this does work, it just doesn't quite feel like the cleanest approach.
I'm fairly new to working with flows, so I don't know if there's some other trick I'm missing...
I ended up implementing something like this:
View Model:
class MessageListViewModel #Inject constructor(
private val repository: Repository,
): ViewModel() {
sealed class UiAction {
class MarkReadError(val error: Throwable): UiAction()
class MarkedRead(val id: Long): UiAction()
}
private val _uiActions = MutableSharedFlow<UiAction>()
val uiActions = _uiActions.asSharedFlow()
.shareIn(
scope = viewModelScope,
started = SharingStarted.WhileSubscribed(),
)
fun markRead(id: Long) {
viewModelScope.launch(Dispatchers.IO) {
try {
repository.markMessageRead(id)
_uiActions.emit(UiAction.MarkedRead(id))
} catch (e: Throwable) {
Log.e(TAG, "Error marking message read: $id", e)
_uiActions.emit(UiAction.MarkReadError(e))
}
}
}
}
View:
#Composable
fun MessageListScreen(
vm: MessageListViewModel = viewModel(),
onMarkReadFailed: (String) -> Unit,
) {
val context = LocalContext.current
val lifecycleOwner = LocalLifecycleOwner.current
val messages: LazyPagingItems<Message> = vm.messages.collectAsLazyPagingItems()
val refreshState = rememberSwipeRefreshState(
isRefreshing = messages.loadState.refresh is LoadState.Loading,
)
LaunchedEffect(lifecycleOwner) {
lifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
vm.uiActions.collectLatest {
when (it) {
is MessageListViewModel.UiAction.MarkReadError -> {
val msg = it.error.localizedMessage ?: it.error.message
val message = if (!msg.isNullOrEmpty()) {
context.getString(R.string.error_unknown_error_with_message, msg)
} else {
context.getString(R.string.error_unknown_error_without_message)
}
onMarkReadFailed(message)
}
is MessageListViewModel.UiAction.MarkedRead -> {
messages.refresh()
}
}
}
}
}
SwipeRefresh(
state = refreshState,
onRefresh = {
messages.refresh()
},
) {
LazyColumn(
modifier = Modifier.fillMaxSize(),
horizontalAlignment = Alignment.CenterHorizontally,
verticalArrangement = Arrangement.Top,
state = listState,
) {
items(
items = messages,
key = { it.id }
) { message ->
message?.let {
MessageRow(
onMarkRead = {
vm.markRead(message.id)
},
)
}
FadedDivider()
}
messages.apply {
when (loadState.append) {
is LoadState.Loading -> {
item {
LoadingRow(R.string.messages_loading)
}
}
else -> {}
}
}
}
}
}
I was developing an App where I try to implement some new technologies, as Jetpack Compose. And in general, it's a great tool, except the fact that it has hard pre-visualize system (#Preview) thn the regular xml design files.
My problem comes when I try to create a #Preview of the component which represent the different rows, where I load my data recover from network.
In my case I made this:
#Preview(
name ="ListScreenPreview ",
showSystemUi = true,
showBackground = true,
device = Devices.NEXUS_9)
#Composable
fun myPokemonRowPreview(
#PreviewParameter(PokemonListScreenProvider::class) pokemonMokData: PokedexListModel
) {
PokedexEntry(
model = pokemonMokData,
navController = rememberNavController(),
viewModel = hiltViewModel())
}
class PokemonListScreenProvider: PreviewParameterProvider<PokedexListModel> {
override val values: Sequence<PokedexListModel> = sequenceOf(
PokedexListModel(
pokemonName = "Cacamon",
number = 0,
imageUrl = "https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/2.png"
),
PokedexListModel(
pokemonName = "Tontaro",
number = 73,
imageUrl = "https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/1.png"
)
)
}
To represent this #Composable:
#Composable
fun PokemonListScreen(
navController: NavController,
viewModel: PokemonListViewModel
) {
Surface(
color = MaterialTheme.colors.background,
modifier = Modifier.fillMaxSize()
)
{
Column {
Spacer(modifier = Modifier.height(20.dp))
Image(
painter = painterResource(id = R.drawable.ic_international_pok_mon_logo),
contentDescription = "Pokemon",
modifier = Modifier
.fillMaxWidth()
.align(CenterHorizontally)
)
SearchBar(
hint = "Search...",
modifier = Modifier
.fillMaxWidth()
.padding(16.dp)
) {
viewModel.searchPokemonList(it)
}
Spacer(modifier = Modifier.height(16.dp))
PokemonList(navController = navController,
viewModel = viewModel)
}
}
}
#Composable
fun SearchBar(
modifier: Modifier = Modifier,
hint: String = " ",
onSearch: (String) -> Unit = { }
) {
var text by remember {
mutableStateOf("")
}
var isHintDisplayed by remember {
mutableStateOf(hint != "")
}
Box(modifier = modifier) {
BasicTextField(value = text,
onValueChange = {
text = it
onSearch(it)
},
maxLines = 1,
singleLine = true,
textStyle = TextStyle(color = Color.Black),
modifier = Modifier
.fillMaxWidth()
.shadow(5.dp, CircleShape)
.background(Color.White, CircleShape)
.padding(horizontal = 20.dp, vertical = 12.dp)
.onFocusChanged {
isHintDisplayed = !it.isFocused
}
)
if (isHintDisplayed) {
Text(
text = hint,
color = Color.LightGray,
modifier = Modifier
.padding(horizontal = 20.dp, vertical = 12.dp)
)
}
}
}
#Composable
fun PokemonList(
navController: NavController,
viewModel: PokemonListViewModel
) {
val pokemonList by remember { viewModel.pokemonList }
val endReached by remember { viewModel.endReached }
val loadError by remember { viewModel.loadError }
val isLoading by remember { viewModel.isLoading }
val isSearching by remember { viewModel.isSearching }
LazyColumn(contentPadding = PaddingValues(16.dp)) {
val itemCount = if (pokemonList.size % 2 == 0) {
pokemonList.size / 2
} else {
pokemonList.size / 2 + 1
}
items(itemCount) {
if (it >= itemCount - 1 && !endReached && !isLoading && !isSearching) {
viewModel.loadPokemonPaginated()
}
PokedexRow(rowIndex = it, models = pokemonList, navController = navController, viewModel = viewModel)
}
}
Box(
contentAlignment = Center,
modifier = Modifier.fillMaxSize()
) {
if (isLoading) {
CircularProgressIndicator(color = MaterialTheme.colors.primary)
}
if (loadError.isNotEmpty()) {
RetrySection(error = loadError) {
viewModel.loadPokemonPaginated()
}
}
}
}
#SuppressLint("LogNotTimber")
#Composable
fun PokedexEntry(
model: PokedexListModel,
navController: NavController,
modifier: Modifier = Modifier,
viewModel: PokemonListViewModel
) {
val defaultDominantColor = MaterialTheme.colors.surface
var dominantColor by remember {
mutableStateOf(defaultDominantColor)
}
Box(
contentAlignment = Center,
modifier = modifier
.shadow(5.dp, RoundedCornerShape(10.dp))
.clip(RoundedCornerShape(10.dp))
.aspectRatio(1f)
.background(
Brush.verticalGradient(
listOf(dominantColor, defaultDominantColor)
)
)
.clickable {
navController.navigate(
"pokemon_detail_screen/${dominantColor.toArgb()}/${model.pokemonName}/${model.number}"
)
}
) {
Column {
CoilImage(
imageRequest = ImageRequest.Builder(LocalContext.current)
.data(model.imageUrl)
.target {
viewModel.calcDominantColor(it) { color ->
dominantColor = color
}
}.build(),
imageLoader = ImageLoader.Builder(LocalContext.current)
.availableMemoryPercentage(0.25)
.crossfade(true)
.build(),
contentDescription = model.pokemonName,
modifier = Modifier
.size(120.dp)
.align(CenterHorizontally),
loading = {
ConstraintLayout(
modifier = Modifier.fillMaxSize()
) {
val indicator = createRef()
CircularProgressIndicator(
//Set constrains dynamically
modifier = Modifier.constrainAs(indicator) {
top.linkTo(parent.top)
bottom.linkTo(parent.bottom)
start.linkTo(parent.start)
end.linkTo(parent.end)
}
)
}
},
// shows an error text message when request failed.
failure = {
Text(text = "image request failed.")
}
)
Log.d("pokemonlist", model.imageUrl)
Text(
text = model.pokemonName,
fontFamily = RobotoCondensed,
fontSize = 20.sp,
textAlign = TextAlign.Center,
modifier = Modifier.fillMaxWidth(),
)
}
}
}
#Composable
fun PokedexRow(
rowIndex: Int,
models: List<PokedexListModel>,
navController: NavController,
viewModel: PokemonListViewModel
) {
Column {
Row {
PokedexEntry(
model = models[rowIndex * 2],
navController = navController,
modifier = Modifier.weight(1f),
viewModel = viewModel
)
Spacer(modifier = Modifier.width(16.dp))
if (models.size >= rowIndex * 2 + 2) {
PokedexEntry(
model = models[rowIndex * 2 + 1],
navController = navController,
modifier = Modifier.weight(1f),
viewModel = viewModel
)
} else {
Spacer(modifier = Modifier.weight(1f))
}
}
Spacer(modifier = Modifier.height(16.dp))
}
}
#Composable
fun RetrySection(
error: String,
onRetry: () -> Unit,
) {
Column() {
Text(error, color = Color.Red, fontSize = 18.sp)
Spacer(modifier = Modifier.height(8.dp))
Button(
onClick = { onRetry() },
modifier = Modifier.align(CenterHorizontally)
) {
Text(text = "Retry")
}
}
}
I try to annotate with the #Nullable navController and viewmodel of the PokemonListScreen #Composable, but doesn't work either. I'm still seeing an empty screen:
So I try to search into the Jetpack documentation but, it's just defining quite simple Composables.
So if you have some more knowledge about it and can help, thanks in advance !
The main problem is if I wanna Preview that #Composable, although I made #Nullable to the viewmodel parameter, which I guess it's the problem here, AS still demand to initialize. Because I guess the right way to pass argument to a preview is by #PreviewArgument annotation.
[EDIT]
After some digging, I found AS is returning the following error under the Preview Screen:
So, there anyway to avoid viewmodel error??
[SOLUTION]
Finally a apply the following solution which make works, because the cause of the problem is due to Hilt have some inconpatibilities with Jetpack Compose previews:
Create an interface of the your ViewModel which recover all the variables and methods.
Make yourcurrent viemodel class extends of the interface.
Create a 2ยบ class which extends on the interface and pass that to your #Preview
#SuppressLint("UnrememberedMutableState")
#Preview(
name ="ListScreenPreview",
showSystemUi = true,
showBackground = true,
device = Devices.PIXEL)
#Composable
fun MyPokemonRowPreview(
#PreviewParameter(PokemonListScreenProvider::class) pokemonMokData: PokedexListModel
) {
JetpackComposePokedexTheme {
PokedexRow(
rowIndex = 0,
models = PokemonListScreenProvider().values.toList(),
navController = rememberNavController(),
viewModel = PokemonListViewModelMock(
0, mutableStateOf(""), mutableStateOf(value = false),
mutableStateOf(false), mutableStateOf(listOf(pokemonMokData))
)
)
}
}
class PokemonListScreenProvider: PreviewParameterProvider<PokedexListModel> {
override val values: Sequence<PokedexListModel> = sequenceOf(
PokedexListModel(
pokemonName = "Machasaurio",
number = 0,
imageUrl = "https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/2.png"
),
PokedexListModel(
pokemonName = "Tontaro",
number = 73,
imageUrl = "https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/1.png"
)
)
}
PokemonListViewModelInterface
interface PokemonListViewModelInterface {
var curPage : Int
var loadError: MutableState<String>
var isLoading: MutableState<Boolean>
var endReached: MutableState<Boolean>
var pokemonList: MutableState<List<PokedexListModel>>
fun searchPokemonList(query: String)
fun loadPokemonPaginated()
fun calcDominantColor(drawable: Drawable, onFinish: (Color) -> Unit)
}
PokemonListViewModelMock
class PokemonListViewModelMock (
override var curPage: Int,
override var loadError: MutableState<String>,
override var isLoading: MutableState<Boolean>,
override var endReached: MutableState<Boolean>,
override var pokemonList: MutableState<List<PokedexListModel>>
): PokemonListViewModelInterface{
override fun searchPokemonList(query: String) {
TODO("Not yet implemented")
}
override fun loadPokemonPaginated() {
TODO("Not yet implemented")
}
override fun calcDominantColor(drawable: Drawable, onFinish: (Color) -> Unit) {
TODO("Not yet implemented")
}
}
The actual Preview is the following, and although the image doesn't display, is shown correctly:
You could create another composable which invokes the viewmodel logic via lambda functions instead of using the viewmodel itself. Extract your uiState to a separate class, so it can be used as a StateFlow in your viewmodel, which in turn can be observed from the composable.
#Composable
fun PokemonListScreen(
navController: NavController,
viewModel: PokemonListViewModel
) {
/*
rememberStateWithLifecyle is an extension function based on
https://medium.com/androiddevelopers/a-safer-way-to-collect-flows-from-android-uis-23080b1f8bda
*/
val uiState by rememberStateWithLifecycle(viewModel.uiState)
PokemonListScreen(
uiState = uiState,
onLoadPokemons = viewModel::loadPokemons,
onSearchPokemon = {viewModel.searchPokemon(it)},
onCalculateDominantColor = {viewModel.calcDominantColor(it)},
onNavigate = {route -> navController.navigate(route, null, null)},
)
}
#Composable
private fun PokemonListScreen(
uiState: PokemonUiState,
onLoadPokemons:()->Unit,
onSearchPokemon: (String) -> Unit,
onCalculateDominantColor: (Drawable) -> Color,
onNavigate:(String)->Unit,
) {
}
#HiltViewModel
class PokemonListViewModel #Inject constructor(/*your datasources*/) {
private val loading = MutableStateFlow(false)
private val loadError = MutableStateFlow(false)
private val endReached = MutableStateFlow(false)
private val searching = MutableStateFlow(false)
private val pokemons = MutableStateFlow<Pokemon?>(null)
val uiState: StateFlow<PokemonUiState> = combine(
loading,
loadError,
endReached,
searching,
pokemons
) { loading, error, endReached, searching, pokemons ->
PokemonUiState(
isLoading = loading,
loadError = error,
endReached = endReached,
isSearching = searching,
pokemonList = pokemons,
)
}.stateIn(
scope = viewModelScope,
started = SharingStarted.WhileSubscribed(5000),
initialValue = PokemonUiState.Empty,
)
}
data class PokemonUiState(
val pokemonList: List<Pokemon> = emptyList(),
val endReached: Boolean = false,
val loadError: Boolean = false,
val isLoading: Boolean = false,
val isSearching: Boolean = false,
) {
companion object {
val Empty = PokemonUiState()
}
}
I'm not sure of the depth of this application, but a potential idea would be to code to an interface and not an implementation.
That is, create an interface with all of the functions you need (that may already exist in your ViewModel), have your PokemonListViewModel implement it, and create another mock class that implements it as well. Pass the mock into your preview and leave the real implementation with PokemonListViewModel
interface PokeListViewModel {
...
// your other val's
val isLoading: Boolean
fun searchPokemonList(pokemon: String)
fun loadPokemonPaginated()
// your other functions
...
}
Once you create your interface you can simply update your composables to be expecting an object that "is a" PokeListViewModel, for example.
Hopefully this helps
I have a main screen where I have retrieved a list string in a viewmodel. I also have a button that opens a Dialog. In this dialog I have a text field for the user to write the word that he want to filter (potato name field), and buttons to filter and cancel.
How can I apply the filter in the viewmodel when the user clicks on the button to accept that on the main screen the list is already filtered?
MainScreen:
#Composable
fun PotatosScreen(
viewModel: PotatosViewModel,
state: Success<PotatosData>
) {
val expandedItem = viewModel.expandedCardList.collectAsState()
Box(
modifier = Modifier.fillMaxSize()
) {
LazyColumn(
modifier = Modifier
.fillMaxSize()
.padding(vertical = 8.dp)
) {
items(state.data.potatos) { potato ->
potatoCard(
potato = potato,
onCardArrowClick = { viewModel.itemArrowClick(potato.id) },
expanded = expandedItem.value.contains(potato.id)
)
}
}
var showCustomDialogWithResult by remember { mutableStateOf(true) }
// Text button for open Dialog
Text(
text = "Filter",
modifier = Modifier
.clickable {
if (showCustomDialogWithResult) {
DialogFilter(
onDismiss = {
showCustomDialogWithResult = !showCustomDialogWithResult
},
onNegativeClick = {
showCustomDialogWithResult = !showCustomDialogWithResult
},
onPositiveClick = {
showCustomDialogWithResult = !showCustomDialogWithResult
}
)
}
}
)
}
}
Dialog:
#Composable
fun DialogFilter(
onDismiss: () -> Unit,
onNegativeClick: () -> Unit,
onPositiveClick: () -> Unit
) {
var text by remember { mutableStateOf("") }
Dialog(onDismissRequest = onDismiss) {
Card(
shape = RoundedCornerShape(10.dp),
modifier = Modifier.padding(10.dp, 5.dp, 10.dp, 10.dp),
elevation = 8.dp
) {
Column(
Modifier.background(Color.White)
) {
Text(
text = stringResource("Filter")
)
TextField(
value = text
)
TextButton(onClick = onNegativeClick) {
Text(
text = "Cancel
)
}
// How apply filter in viewModel here?
TextButton(onClick = onPositiveClick) {
Text(
text = "Filter"
)
}
}
}
}
}
ViewModel:
#HiltViewModel
class PotatosViewModel #Inject constructor(
private val getPotatosDataUseCase: GetPotatosData
) : ViewModel() {
private val _state = mutableStateOf<Response<PotatosData>>(Loading)
val state: State<Response<PotatosData>> = _state
private val _expandedItemList = MutableStateFlow(listOf<Int>())
val expandedCardList: StateFlow<List<Int>> get() = _expandedItemList
private val _isRefreshing = MutableStateFlow(false)
val isRefreshing: StateFlow<Boolean>
get() = _isRefreshing.asStateFlow()
init {
getPotatos()
}
fun refresh() {
viewModelScope.launch {
_isRefreshing.emit(true)
getPotatos()
_isRefreshing.emit(false)
}
}
private fun getPotatos() {
viewModelScope.launch {
getPotatosDataUseCase().collect { response ->
_state.value = response
}
}
}
fun containsItem(potatoId: Int): Boolean {
return _expandedItemList.value.toMutableList().contains(potatoId)
}
fun itemArrowClick(potatoId: Int) {
_expandedItemList.value = _expandedItemList.value.toMutableList().also { list ->
if (list.contains(potatoId)) {
list.remove(potatoId)
} else {
list.add(potatoId)
}
}
}
}
State:
data class PotatosState(
val potatoes: List<Potato>,
)
Potato:
data class Potato(
val id: Int,
val name: String)
You can change the onPositiveClick callback to accept a String and pass it to the ViewModel in order to apply your filter, something like this:
fun DialogFilter(
onDismiss: () -> Unit,
onNegativeClick: () -> Unit,
onPositiveClick: (String) -> Unit
)
And then the callback would call your ViewModel with the text
onPositiveClick = { filter ->
showCustomDialogWithResult = !showCustomDialogWithResult
viewModel.applyFilter(filter)
}
Edit 1
TextButton(onClick = {
onPositiveClick(text)
}) {
Text(
text = "Filter"
)
}
I am trying to do pagination in my application. First, I'm fetching 20 item from Api (limit) and every time i scroll down to the bottom of the screen, it increase this number by 20 (nextPage()). However, when this function is called, the screen goes to the top, but I want it to continue where it left off. How can I do that?
Here is my code:
CharacterListScreen:
#Composable
fun CharacterListScreen(
characterListViewModel: CharacterListViewModel = hiltViewModel()
) {
val state = characterListViewModel.state.value
val limit = characterListViewModel.limit.value
Box(modifier = Modifier.fillMaxSize()) {
val listState = rememberLazyListState()
LazyColumn(modifier = Modifier.fillMaxSize(), state = listState) {
itemsIndexed(state.characters) { index, character ->
characterListViewModel.onChangeRecipeScrollPosition(index)
if ((index + 1) >= limit) {
characterListViewModel.nextPage()
}
CharacterListItem(character = character)
}
}
if (state.error.isNotBlank()) {
Text(
text = state.error,
color = MaterialTheme.colors.error,
textAlign = TextAlign.Center,
modifier = Modifier
.fillMaxWidth()
.padding(horizontal = 20.dp)
.align(Alignment.Center)
)
}
if (state.isLoading) {
CircularProgressIndicator(modifier = Modifier.align(Alignment.Center))
}
}
}
CharacterListViewModel:
#HiltViewModel
class CharacterListViewModel #Inject constructor(
private val characterRepository: CharacterRepository
) : ViewModel() {
val state = mutableStateOf(CharacterListState())
val limit = mutableStateOf(20)
var recipeListScrollPosition = 0
init {
getCharacters(limit.value, Constants.HEADER)
}
private fun getCharacters(limit : Int, header : String) {
characterRepository.getCharacters(limit, header).onEach { result ->
when(result) {
is Resource.Success -> {
state.value = CharacterListState(characters = result.data ?: emptyList())
}
is Resource.Error -> {
state.value = CharacterListState(error = result.message ?: "Unexpected Error")
}
is Resource.Loading -> {
state.value = CharacterListState(isLoading = true)
}
}
}.launchIn(viewModelScope)
}
private fun incrementLimit() {
limit.value = limit.value + 20
}
fun onChangeRecipeScrollPosition(position: Int){
recipeListScrollPosition = position
}
fun nextPage() {
if((recipeListScrollPosition + 1) >= limit.value) {
incrementLimit()
characterRepository.getCharacters(limit.value, Constants.HEADER).onEach {result ->
when(result) {
is Resource.Success -> {
state.value = CharacterListState(characters = result.data ?: emptyList())
}
is Resource.Error -> {
state.value = CharacterListState(error = result.message ?: "Unexpected Error")
}
is Resource.Loading -> {
state.value = CharacterListState(isLoading = true)
}
}
}.launchIn(viewModelScope)
}
}
}
CharacterListState:
data class CharacterListState(
val isLoading : Boolean = false,
var characters : List<Character> = emptyList(),
val error : String = ""
)
I think the issue here is that you are creating CharacterListState(isLoading = true) while loading. This creates an object with empty list of elements. So compose renders an empty LazyColumn here which resets the scroll state. The easy solution for that could be state.value = state.value.copy(isLoading = true). Then, while loading, the item list can be preserved (and so is the scroll state)
Not sure if you are using the LazyListState correctly. In your viewmodel, create an instance of LazyListState:
val lazyListState: LazyListState = LazyListState()
Pass that into your composable and use it as follows:
#Composable
fun CharacterListScreen(
characterListViewModel: CharacterListViewModel = hiltViewModel()
) {
val limit = characterListViewModel.limit.value
Box(modifier = Modifier.fillMaxSize()) {
LazyColumn(modifier = Modifier.fillMaxSize(), state = characterListViewModel.lazyListState) {
itemsIndexed(state.characters) { index, character ->
}
}
}
}