Following the Pathway code labs from Google about Jetpack compose, I was trying out this code
import android.os.Bundle
import androidx.activity.compose.setContent
import androidx.appcompat.app.AppCompatActivity
import androidx.compose.animation.animateColorAsState
import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxHeight
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.material.Button
import androidx.compose.material.ButtonDefaults
import androidx.compose.material.Divider
import androidx.compose.material.Surface
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import com.codelab.basics.ui.BasicsCodelabTheme
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MyApp {
MyScreenContent()
}
}
}
}
#Composable
fun MyApp(content: #Composable () -> Unit) {
BasicsCodelabTheme {
Surface(color = Color.Yellow) {
content()
}
}
}
#Composable
fun MyScreenContent(names: List<String> = List(1000) { "Hello Android #$it" }) {
val counterState = remember { mutableStateOf(0) }
Column(modifier = Modifier.fillMaxHeight()) {
NameList(names, Modifier.weight(1f))
Counter(
count = counterState.value,
updateCount = { newCount ->
counterState.value = newCount
}
)
}
}
#Composable
fun NameList(names: List<String>, modifier: Modifier = Modifier) {
LazyColumn(modifier = modifier) {
items(items = names) { name ->
Greeting(name = name)
Divider(color = Color.Black)
}
}
}
#Composable
fun Greeting(name: String) {
var isSelected by remember { mutableStateOf(false) }
val backgroundColor by animateColorAsState(if (isSelected) Color.Red else Color.Transparent)
Text(
text = "Hello $name!",
modifier = Modifier
.padding(24.dp)
.background(color = backgroundColor)
.clickable(onClick = { isSelected = !isSelected })
)
}
#Composable
fun Counter(count: Int, updateCount: (Int) -> Unit) {
Button(
onClick = { updateCount(count + 1) },
colors = ButtonDefaults.buttonColors(
backgroundColor = if (count > 5) Color.Green else Color.White
)
) {
Text("I've been clicked $count times")
}
}
#Preview("MyScreen preview")
#Composable
fun DefaultPreview() {
MyApp {
MyScreenContent()
}
}
I have noticed that LazyColumn will recompose the items whenever they become Visible on the screen (intended behaviour!) however, the Local state of Greeting widget is completely lost!
I believe this is a bug in Compose, Ideally the composer should consider the remember cached state. Is there an elegant way to fix this?
Thanks in advance!
[Update]
Using rememberSaveable {...} gives the power to survive the android change of configuration as well as the scrollability
Docs
Remember the value produced by init.
It behaves similarly to remember, but the stored value will survive the activity or process recreation using the saved instance state mechanism (for example it happens when the screen is rotated in the Android application).
The code now is more elegant and shorter, we don't even need to hoist the state, it can be kept internal. The only thing I am not so sure of now with using rememberSaveable is if there will be any performance penalties when the list grows bigger and bigger, say 1000 items.
#Composable
fun Greeting(name: String) {
val isSelected = rememberSaveable { mutableStateOf(false) }
val backgroundColor by animateColorAsState(if (isSelected.value) Color.Red else Color.Transparent)
Text(
text = "Hello $name! selected: ${isSelected.value}",
modifier = Modifier
.padding(24.dp)
.background(color = backgroundColor)
.clickable(onClick = {
isSelected.value = !isSelected.value
})
)
}
[Original Answer]
Based on #CommonWare's answer The LazyColumn will dispose the composables along with their states when they are off-screen this means when LazyColumn recomposes the Compsoables again it will have fresh start state. To fix this issue all that has to be done is to hoist the state to the consumer's scope, LazyColumn in this case.
Also we need to use mutableStateMapOf() instead of MutableMapOf inside the remember { ... } lambda or Compose-core engine will not be aware of this change.
So far here is the code:
#Composable
fun NameList(names: List<String>, modifier: Modifier = Modifier) {
val selectedStates = remember {
mutableStateMapOf<Int, Boolean>().apply {
names.mapIndexed { index, _ ->
index to false
}.toMap().also {
putAll(it)
}
}
}
LazyColumn(modifier = modifier) {
itemsIndexed(items = names) { index, name ->
Greeting(
name = name,
isSelected = selectedStates[index] == true,
onSelected = {
selectedStates[index] = !it
}
)
Divider(color = Color.Black)
}
}
}
Happy composing!
Related
I copied a piece of code from the example in jetpack compose.link
But in Android Studio a problem arises:
I wonder where is the problem? I'm still a beginner
The following is the complete code:
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.material.*
import androidx.compose.material.MaterialTheme.colors
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Menu
import androidx.compose.runtime.Composable
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import com.freedom.android.ui.theme.MyApplicationTheme
import kotlinx.coroutines.launch
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MyApplicationTheme {
val scaffoldState = rememberScaffoldState()
val scope = rememberCoroutineScope()
Scaffold(
scaffoldState = scaffoldState,
drawerContent = { Text("Drawer content") },
topBar = {
TopAppBar(
title = { Text("Simple Scaffold Screen") },
navigationIcon = {
IconButton(
onClick = {
scope.launch { scaffoldState.drawerState.open() }
}
) {
Icon(Icons.Filled.Menu, contentDescription = "Localized description")
}
}
)
},
floatingActionButtonPosition = FabPosition.End,
floatingActionButton = {
ExtendedFloatingActionButton(
text = { Text("Inc") },
onClick = { /* fab click handler */ }
)
},
content = { innerPadding ->
LazyColumn(contentPadding = innerPadding) {
items(count = 100) {
Box(
Modifier
.fillMaxWidth()
.height(50.dp)
.background(colors[it % colors.size])
)
}
}
}
)
}
}
}
}
#Composable
fun Greeting(name: String) {
Text(text = "Hello $name!")
}
#Preview(showBackground = true)
#Composable
fun DefaultPreview() {
MyApplicationTheme {
Greeting("Android")
}
}
I think the problem is with the colors variable, it doesn't seem to be an array, but this was copied from the official documentation, I didn't change it.
package androidx.compose.material
object MaterialTheme {
/**
* Retrieves the current [Colors] at the call site's position in the hierarchy.
*
* #sample androidx.compose.material.samples.ThemeColorSample
*/
val colors: Colors
#Composable
#ReadOnlyComposable
get() = LocalColors.current
}
If you look at the full source code of the sample the docs use, it has a top level object:
private val colors = listOf(
Color(0xFFffd7d7.toInt()),
Color(0xFFffe9d6.toInt()),
Color(0xFFfffbd0.toInt()),
Color(0xFFe3ffd9.toInt()),
Color(0xFFd0fff8.toInt())
)
So yeah, the colors that sample is referring to is a list that you can index into. If you want to also have a semi-random set of colors for your backgrounds, you can copy that list into your code as well.
I am currently trying to write an Android Application that makes API calls to retrieve the estimated arrival timings of the incoming buses. The ViewModel files shows me using my Bus Repository to make the API Call, where listResult contains the data I want.
How can I pass the API Call I made to one of my Android Application's screens? I'm supposed to use the UiState Variable to do so right? Thank you.
The Pastebin contains my code as well if it's easier to see there!!
AppViewModel.kt
https://pastebin.com/qPVrDF9i
package com.example.busexpress.ui.screens
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelProvider.AndroidViewModelFactory.Companion.APPLICATION_KEY
import androidx.lifecycle.viewModelScope
import androidx.lifecycle.viewmodel.initializer
import androidx.lifecycle.viewmodel.viewModelFactory
import com.example.busexpress.BusExpressApplication
import com.example.busexpress.data.SingaporeBusRepository
import com.example.busexpress.network.SingaporeBus
import kotlinx.coroutines.launch
import retrofit2.HttpException
import java.io.IOException
/**
* [AppViewModel] holds information about a cupcake order in terms of quantity, flavor, and
* pickup date. It also knows how to calculate the total price based on these order details.
*/
class AppViewModel(private val singaporeBusRepository: SingaporeBusRepository): ViewModel() {
/** The mutable State that stores the status of the most recent request */
var busUiState: BusUiState by mutableStateOf(BusUiState.Loading) // Loading as Default Value
// Setter is private to protect writes to the busUiState
private set
/**
* Call init so we can display status immediately.
*/
init {
getBusTimings(null)
}
fun getBusTimings(userInput: String?) {
// Determine if UserInput is a BusStopCode
var busStopCode: String?
var busServiceNumber: String?
val userInputLength = userInput?.length ?: 0
if (userInputLength == 5) {
// Bus Stop Code
busStopCode = userInput
busServiceNumber = null
}
else {
// Bus Service Number
busStopCode = null
busServiceNumber = userInput
}
// Launch the Coroutine using a ViewModelScope
viewModelScope.launch {
busUiState = BusUiState.Loading
// Might have Connectivity Issues
busUiState = try {
// Within this Scope, use the Repository, not the Object to access the Data, abstracting the data within the Data Layer
val listResult: SingaporeBus = singaporeBusRepository.getBusTimings(
busServiceNumber = busServiceNumber,
busStopCode = busStopCode
)
// Assign results from backend server to busUiState {A mutable state object that represents the status of the most recent web request}
BusUiState.Success(timings = listResult)
}
catch (e: IOException) {
BusUiState.Error
}
catch (e: HttpException) {
BusUiState.Error
}
}
}
// Factory Object to retrieve the singaporeBusRepository and pass it to the ViewModel
companion object {
val Factory: ViewModelProvider.Factory = viewModelFactory {
initializer {
val application = (this[APPLICATION_KEY] as BusExpressApplication)
val singaporeBusRepository = application.container.singaporeBusRepository
AppViewModel(singaporeBusRepository = singaporeBusRepository)
}
}
}
// private val _uiState = MutableStateFlow(AppUiState(65199))
// val uiState: StateFlow<AppUiState> = _uiState.asStateFlow()
}
// Simply saving the UiState as a Mutable State prevents us from saving the different status
// like Loading, Error, and Success
sealed interface BusUiState {
data class Success(val timings: SingaporeBus) : BusUiState
// The 2 States below need not set new data and create new objects, which is why an object is sufficient for the web response
object Error: BusUiState
object Loading: BusUiState
// Sealed Interface used instead of Interface to remove Else Branch
}
Example: DefaultScreen.kt
https://pastebin.com/UiZPwZHG
package com.example.busexpress.ui.screens
import androidx.annotation.StringRes
import androidx.compose.foundation.Image
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.foundation.text.KeyboardActions
import androidx.compose.foundation.text.KeyboardOptions
import androidx.compose.material.*
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Close
import androidx.compose.material.icons.filled.Search
import androidx.compose.runtime.Composable
import androidx.compose.runtime.MutableState
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.res.painterResource
import androidx.compose.ui.res.stringResource
import androidx.compose.ui.text.input.ImeAction
import androidx.compose.ui.text.input.KeyboardType
import androidx.compose.ui.text.input.TextFieldValue
import androidx.compose.ui.unit.dp
import androidx.lifecycle.viewmodel.compose.viewModel
import androidx.navigation.NavController
import com.example.busexpress.BusExpressApp
import com.example.busexpress.BusExpressScreen
import com.example.busexpress.R
import com.example.busexpress.network.SingaporeBus
import com.example.busexpress.ui.component.BusStopComposable
#Composable
fun DefaultScreen(
busUiState: BusUiState,
modifier: Modifier = Modifier,
appViewModel: AppViewModel = viewModel(),
// navController: NavController
) {
// Mutable State for User Input
var userInput = remember {
mutableStateOf(TextFieldValue(""))
}
Column(
modifier = modifier
.fillMaxWidth()
.padding(16.dp),
) {
// Search Field for Bus Stop or Bus Numbers
SearchView(
label = R.string.search_field_instructions,
state = userInput,
keyboardOptions = KeyboardOptions(
keyboardType = KeyboardType.Number,
imeAction = ImeAction.Search
),
onKeyboardSearch = {
appViewModel.getBusTimings(userInput.value.text)
// navController.navigate(BusExpressScreen.Search.name)
}
)
val busArrivalsJson = appViewModel.getBusTimings(userInput.value.text)
when(busUiState) {
is BusUiState.Success -> ResultScreen(busUiState = busUiState, busArrivalsJSON = busArrivalsJson)
is BusUiState.Loading -> LoadingScreen()
is BusUiState.Error -> ErrorScreen()
else -> ErrorScreen()
}
}
}
#Composable
fun LoadingScreen(modifier: Modifier = Modifier) {
Box(
contentAlignment = Alignment.Center,
modifier = modifier
.fillMaxSize()
) {
Image(
modifier = Modifier.size(200.dp),
painter = painterResource(id = R.drawable.loading_img),
contentDescription = stringResource(R.string.loading_flavor_text)
)
}
}
#Composable
fun ErrorScreen(modifier: Modifier = Modifier) {
Box(
contentAlignment = Alignment.Center,
modifier = modifier.fillMaxSize()
) {
Text(text = stringResource(R.string.loading_failed_flavor_text))
}
}
/**
* The home screen displaying result of fetching photos.
*/
#Composable
fun ResultScreen(
busUiState: BusUiState,
busArrivalsJSON: SingaporeBus
modifier: Modifier = Modifier,
) {
// Results of Search
BusStopComposable(
busArrivalsJSON = busArrivalsJSON,
modifier = modifier
)
// Box(
// contentAlignment = Alignment.Center,
// modifier = modifier.fillMaxSize()
// ) {
// Text(busUiState.toString())
// }
}
#Composable
fun SearchView(
#StringRes label: Int,
state: MutableState<TextFieldValue>,
modifier: Modifier = Modifier,
keyboardOptions: KeyboardOptions,
onKeyboardSearch: () -> Unit,
) {
Column() {
TextField(
value = state.value,
onValueChange = {value ->
state.value = value
},
label = {
if (state.value == TextFieldValue("")) {
Text(
stringResource(id = label),
modifier = Modifier
.fillMaxWidth(),
style = MaterialTheme.typography.h6
)
}
},
modifier = modifier
.fillMaxWidth(),
singleLine = true,
// Search Icon at the Start for Aesthetics
leadingIcon = {
Icon(
imageVector = Icons.Filled.Search,
contentDescription = null,
modifier = Modifier.padding(10.dp)
)
},
// Cancel Button to delete all Input
trailingIcon = {
// Icon appears iif the Search Field is not Empty
if (state.value != TextFieldValue("")) {
IconButton(onClick = {
// Clear the Search Field
state.value = TextFieldValue("")
}) {
Icon(
imageVector = Icons.Filled.Close,
contentDescription = "Delete all User Input",
modifier = Modifier.padding(10.dp)
)
}
}
},
keyboardActions = KeyboardActions(
onSearch = { onKeyboardSearch() }
),
keyboardOptions = keyboardOptions,
shape = RoundedCornerShape(25)
)
Row() {
Spacer(modifier = modifier.weight(3f))
// Button for User to Click to begin Search
Button(
onClick = {
// TODO Pass the User Query to the Search Function
onKeyboardSearch()
},
modifier = modifier
.align(Alignment.CenterVertically)
.padding(2.dp)
.weight(1f),
) {
Text(text = stringResource(R.string.search_button_flavor_text))
}
}
}
}
BusApi.kt (Contains the function to make the API Call)
https://pastebin.com/miAt8x8H
package com.example.busexpress.network
import com.example.busexpress.LTA_API_SECRET_KEY
import retrofit2.http.GET
import retrofit2.http.Headers
import retrofit2.http.Query
interface BusApiService {
/**
* Function to get JSON Objects from URI by specifying Type of Request and Endpoint like "/photos" a URL of sorts
*/
// 1. Returns Bus Timings for Bus Stop and/or Service Number
#Headers(
"accept: application/json",
"AccountKey: $LTA_API_SECRET_KEY"
)
#GET("BusArrivalv2")
suspend fun getTimingsOfBusStop(
#Query("BusStopCode") BusStopCode: String? = null,
#Query("ServiceNo") ServiceNo: String? = null
): SingaporeBus
// 2. Returns the details for all the Bus Stops in Singapore
#Headers(
"accept: application/json",
"AccountKey: $LTA_API_SECRET_KEY"
)
#GET("BusStops")
suspend fun getDetailsOfBusStop(): BusStop
}
You can use SharedViewModel to share the data between the Fragments hosted by a common parent activity or between parent activity and its child fragments as per your need.
For eg, You can declare a MutableStateFlow variable in the SharedViewModel, set its value when you receive response from API call (which you trigger from one Fragment or parent activity) and then collect the value of that flow via the same SharedViewModel inside child Fragment and update the UI accordingly.
Refer https://developer.android.com/codelabs/basic-android-kotlin-training-shared-viewmodel#0
I am new to Jetpack compose. I am following the tutorial and the problem is that according to the tutorial the text color is black on the preview as well as on the real device (in the tutorial)
on my preview I also see the color as black, however, when I run the app on my two different devices I see the color is white.
What am I missing here?
UPD
package com.example.composableexmp
import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.CornerSize
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.MaterialTheme
import androidx.compose.material.Surface
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import com.example.composableexmp.ui.theme.ComposableExmpTheme
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MyApp {
TopHeader()
}
}
}
}
#Composable
fun MyApp(content: #Composable () -> Unit) {
ComposableExmpTheme {
Surface(
color = MaterialTheme.colors.background
) {
content()
}
}
}
#Preview
#Composable
fun TopHeader(totalPerPerson: Double = 0.0) {
Surface(
modifier = Modifier
.fillMaxWidth()
.height(150.dp)
.clip(shape = RoundedCornerShape(corner = CornerSize(12.dp))),
color = Color(color = 0xFFE9D7F7)
) {
Column(
modifier = Modifier.padding(12.dp),
horizontalAlignment = Alignment.CenterHorizontally,
verticalArrangement = Arrangement.Center
) {
val total = "%.2f".format(totalPerPerson)
Text(
text = "Total Per Person",
style = MaterialTheme.typography.h5
)
Text(
text = "$$total",
style = MaterialTheme.typography.h4,
fontWeight = FontWeight.ExtraBold
)
}
}
}
#Preview(showBackground = true)
#Composable
fun DefaultPreview() {
ComposableExmpTheme {
MyApp {
Text(text = "Hello Again")
}
}
}
Colors change based on your theme. You should inspect Theme.kt in ui.theme folder.
private val DarkColorScheme = darkColorScheme(
primary = Purple80,
secondary = PurpleGrey80,
tertiary = Pink80
)
private val LightColorScheme = lightColorScheme(
primary = Purple40,
secondary = PurpleGrey40,
tertiary = Pink40
/* Other default colors to override
background = Color(0xFFFFFBFE),
surface = Color(0xFFFFFBFE),
onPrimary = Color.White,
onSecondary = Color.White,
onTertiary = Color.White,
onBackground = Color(0xFF1C1B1F),
onSurface = Color(0xFF1C1B1F),
*/
)
And how these colors are selected
#Composable
fun MyTheme(
darkTheme: Boolean = isSystemInDarkTheme(),
// Dynamic color is available on Android 12+
dynamicColor: Boolean = true,
content: #Composable () -> Unit
) {
val colorScheme = when {
dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
val context = LocalContext.current
if (darkTheme) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
}
darkTheme -> DarkColorScheme
else -> LightColorScheme
}
val view = LocalView.current
if (!view.isInEditMode) {
SideEffect {
(view.context as Activity).window.statusBarColor = colorScheme.primary.toArgb()
ViewCompat.getWindowInsetsController(view)?.isAppearanceLightStatusBars = darkTheme
}
}
MaterialTheme(
colorScheme = colorScheme,
typography = Typography,
content = content
)
}
On Surface is the color of the Text provided by Surface. Based on your theme it can be the values set to these colors.
I have implemented 2 bottom sheets in the ModalBottomSheetLayout, both bottom sheets has a list of item checkable with checkbox.
The state of the screen is managed by the viewModel and when the selection changes is invoked a function that copies the state with the new value of the selected text.
When the bottom sheet opens the selection is correct but when I click to change the selection, the bottomsheet is not recomposed and the selection does not change, but in the main screen the state change is correctly read and the value is updated.
Here my code:
MainScreen:
import androidx.compose.foundation.layout.*
import androidx.compose.material.*
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import kotlinx.coroutines.launch
#ExperimentalMaterialApi
#Composable
fun MainScreen(
viewModel: MainViewModel = androidx.lifecycle.viewmodel.compose.viewModel()
) {
val screenState = viewModel.screenState
val scope = rememberCoroutineScope()
val bottomSheetState = rememberModalBottomSheetState(
initialValue = ModalBottomSheetValue.Hidden
)
var bottomSheetContent: (#Composable () -> Unit)? by remember {
mutableStateOf(null)
}
ModalBottomSheetLayout(
sheetState = bottomSheetState,
sheetContent = {
Box(
modifier = Modifier.defaultMinSize(minHeight = 1.dp)
) {
bottomSheetContent?.let { it() }
}
}
) {
Column(
modifier = Modifier
.fillMaxSize()
.padding(16.dp)
) {
Text(text = "First BottomSheet", style = MaterialTheme.typography.h6)
Text(
text = "Selected: ${screenState.selectedTextFromFirstBottomSheet}",
Modifier.padding(16.dp)
)
Button(onClick = {
bottomSheetContent = {
FirstBottomSheet(
selectedText = screenState.selectedTextFromFirstBottomSheet,
onSelected = { text ->
viewModel.onEvent(
MainScreenEvent.OnFirstBottomSheetSelectedTextChanged(text)
)
},
textList = screenState.firstBottomSheetTextList
)
}
scope.launch {
bottomSheetState.show()
}
}, modifier = Modifier.padding(16.dp)) {
Text(text = " Open First BottomSheet")
}
Text(text = "Second BottomSheet", style = MaterialTheme.typography.h6)
Text(
text = "Selected: ${screenState.selectedTextFromSecondBottomSheet}",
Modifier.padding(16.dp)
)
Button(
onClick = {
bottomSheetContent = {
SecondBottomSheet(
selectedText = screenState.selectedTextFromSecondBottomSheet,
onSelected = { text ->
viewModel.onEvent(
MainScreenEvent.OnSecondBottomSheetSelectedTextChanged(text)
)
},
textList = screenState.secondBottomSheetTextList
)
}
scope.launch {
bottomSheetState.show()
}
}, modifier = Modifier
.padding(16.dp)
) {
Text(text = " Open Second BottomSheet")
}
}
}
}
ViewModel:
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.lifecycle.ViewModel
class MainViewModel : ViewModel(){
var screenState by mutableStateOf(MainScreenState())
fun onEvent(event: MainScreenEvent){
when(event){
is MainScreenEvent.OnFirstBottomSheetSelectedTextChanged -> {
screenState = screenState.copy(
selectedTextFromFirstBottomSheet = event.text
)
}
is MainScreenEvent.OnSecondBottomSheetSelectedTextChanged -> {
screenState = screenState.copy(
selectedTextFromSecondBottomSheet = event.text
)
}
}
}
}
ScreenState
data class MainScreenState(
val selectedTextFromFirstBottomSheet: String = "First Text b1",
val selectedTextFromSecondBottomSheet: String = "Third Text b2",
val firstBottomSheetTextList: List<String> = listOf(
"First Text b1",
"Second Text b1",
"Third Text b1",
"Fourth Text b1",
"Five Text b1"
),
val secondBottomSheetTextList: List<String> = listOf(
"First Text b2",
"Second Text b2",
"Third Text b2",
"Fourth Text b2",
"Five Text b2"
)
)
Screen Event
sealed class MainScreenEvent(){
data class OnFirstBottomSheetSelectedTextChanged(val text: String): MainScreenEvent()
data class OnSecondBottomSheetSelectedTextChanged(val text: String): MainScreenEvent()
}
First Bottom Sheet
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.selection.toggleable
import androidx.compose.material.Checkbox
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.semantics.Role
import androidx.compose.ui.unit.dp
#Composable
fun FirstBottomSheet(
selectedText: String,
textList: List<String>,
onSelected: (text: String) -> Unit
) {
Column(
modifier = Modifier
.fillMaxWidth()
.padding(16.dp)
) {
textList.forEach { text ->
Row(modifier = Modifier
.fillMaxWidth()
.toggleable(
value = selectedText == text,
role = Role.Checkbox,
onValueChange = { isSelected ->
if (isSelected) {
onSelected(text)
}
}
)
.padding(16.dp),
verticalAlignment = Alignment.CenterVertically
) {
Text(text = text, modifier = Modifier.weight(1f))
Checkbox(checked = selectedText == text, onCheckedChange = null)
}
}
}
}
Second Bottom Sheet
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.selection.toggleable
import androidx.compose.material.Checkbox
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.semantics.Role
import androidx.compose.ui.unit.dp
#Composable
fun SecondBottomSheet(
selectedText: String,
textList: List<String>,
onSelected: (text: String) -> Unit
) {
Column(
modifier = Modifier
.fillMaxWidth()
.padding(16.dp)
) {
textList.forEach { text ->
Row(modifier = Modifier
.fillMaxWidth()
.toggleable(
value = selectedText == text,
role = Role.Checkbox,
onValueChange = { isSelected ->
if (isSelected) {
onSelected(text)
}
}
)
.padding(16.dp),
verticalAlignment = Alignment.CenterVertically) {
Text(text = text, modifier = Modifier.weight(1f))
Checkbox(checked = selectedText == text, onCheckedChange = null)
}
}
}
}
Thanks for your help!
I copied and pasted your code. The only changes I made were:
Remove this line from MainScreen
val screenState = viewModel.screenState
Access the state directly.
Text(
text = "Selected: ${viewModel.screenState.selectedTextFromFirstBottomSheet}",
Modifier.padding(16.dp)
)
Button(onClick = {
bottomSheetContent = {
FirstBottomSheet(
selectedText = viewModel.screenState.selectedTextFromFirstBottomSheet,
onSelected = { text ->
viewModel.onEvent(
MainScreenEvent.OnFirstBottomSheetSelectedTextChanged(text)
)
},
textList = viewModel.screenState.firstBottomSheetTextList
)
}
scope.launch {
bottomSheetState.show()
}
}, modifier = Modifier.padding(16.dp)) {
Text(text = " Open First BottomSheet")
}
Boom! It worked :)
My understanding is: you're creating a variable containing the value of a state, but you're not listening to the state changes, so the Compose doesn't know the state has changed, therefore the recomposition doesn't happen. The by keyword in your state declaration is a property delegate which set/get the current value of state, but not register the composable to react to these changes.
There are another solutions you can use to observe the state without repeat viewModel.screenState:
Using derivedStateOf:
val screenState by remember {
derivedStateOf {
viewModel.screenState
}
}
Changing the screenState declaration.
// Using "=" instead of "by"
var screenState = mutableStateOf(MainScreenState())
and then use screenState.value to set/get the state value.
And in the screen, use like below:
val screenState = viewModel.screenState
I had the exact same use case in my app but everything was working fine until I updated some of the compose libraries.
I am seeing a weird image flickering issue with Jetpack compose. It is a simple two card deck where the top image is animated off-screen to reveal the second card. The second card displays fine for a second and then the first image flashes on the screen. I have tried with Coil, Fresco and Glide and they all behave the same way.
import androidx.activity.compose.setContent
import androidx.activity.viewModels
import androidx.compose.animation.core.Animatable
import androidx.compose.foundation.Image
import androidx.compose.foundation.background
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.*
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.livedata.observeAsState
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.IntOffset
import androidx.compose.ui.unit.dp
import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import coil.compose.rememberImagePainter
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlin.math.roundToInt
class MainViewModel : ViewModel() {
var images = MutableLiveData(listOf(
"https://images.pexels.com/photos/212286/pexels-photo-212286.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/163016/crash-test-collision-60-km-h-distraction-163016.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/1366944/pexels-photo-1366944.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/5878501/pexels-photo-5878501.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/3846022/pexels-photo-3846022.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
))
}
class MainActivity : ComponentActivity() {
private val model by viewModels<MainViewModel>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
MainScreen(model)
}
}
}
#Composable
fun MainScreen(model: MainViewModel) {
val images: List<String> by model.images.observeAsState(listOf())
Box(
modifier = Modifier.fillMaxSize()
) {
images?.take(2).reversed().forEach {
Card(url = it) {
val d = model.images.value?.toMutableList()
d?.let {
it.removeFirst()
model.images.value = it
}
}
}
}
}
#Composable
fun Card(
url: String,
advance: ()-> Unit = {},
){
val coroutineScope = rememberCoroutineScope()
var offsetX = remember(url) { Animatable(0f) }
Box(
modifier = Modifier
.offset { IntOffset(offsetX.value.roundToInt(), 0) }
.fillMaxSize()
.background(color = Color.White)
.clickable {
coroutineScope.launch {
offsetX.animateTo(
targetValue = 3000F
)
}
coroutineScope.launch {
delay(400)
advance()
}
}
) {
Image(
painter = rememberImagePainter(
data = url,
),
contentDescription = null,
modifier = Modifier
.size(400.dp, 400.dp)
)
}
}
Also threw it on a github here in case anyone wants to try it out:
https://github.com/studentjet/learncompose
The problem is this: you have two card views. After deleting the top card, compose reuses them and updates them with the new data. And while the top card loads the second image, it still shows the first one.
You could disable caching, but in that case the image would still flash because it would show an empty space first. Instead, you need to have the second card's view reused for the first one.
Especially for such cases key Composable is made for: it'll reuse content for the same key between recompositions even if order changes.
val images = remember {
mutableStateListOf(
"https://images.pexels.com/photos/212286/pexels-photo-212286.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/163016/crash-test-collision-60-km-h-distraction-163016.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/1366944/pexels-photo-1366944.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/5878501/pexels-photo-5878501.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
"https://images.pexels.com/photos/3846022/pexels-photo-3846022.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500",
)
}
Box(
modifier = Modifier.fillMaxSize()
) {
images.take(2).reversed().forEach {
key(it) {
Card(url = it) {
images.add(
images.removeFirst()
)
}
}
}
}