I have Onboarding Screens for my project, and it work correctly, but I want to show users it just once, and I was using shared preferences for it, and when debug the project it is throw an error like that in logcat,
List contains no element matching the predicate.
, and in android emulator I can see main screen, but app crash quickly, when I open app again on simulator, onboarding screen shows just 1 second and open main screen, than app crash, I do not know why? I guess problem is because of this line of code,
if (!sharedPreferences.getBoolean("firstTime", true)) {
navController.navigate("main")
}else{
but I am not sure.
mainscreen:
@Composable
fun MainScreen(
navController: NavController,
) {
Column(
Modifier
.fillMaxSize()
,
horizontalAlignment = Alignment.CenterHorizontally
) {
Text(
"WELCOME TO",
modifier = Modifier
.width(300.dp)
,
textAlign = TextAlign.Start,
fontSize = 15.sp,
color = custom,
fontWeight = FontWeight.Medium
)
}
nav:
@OptIn(ExperimentalPagerApi::class)
@Composable
fun NavScreen(
sharedPreferences: SharedPreferences
) {
val navController = rememberNavController()
NavHost(navController = navController, startDestination = "onBoard") {
composable("onBoard", ) {
OnBoardScreen(navController = navController, sharedPreferences)
}
composable("main") {
MainScreen(navController = navController)
}
}
viewmodel:
class OnBoardViewModel (
) : ViewModel() {
private val _currentPage = MutableStateFlow(0)
val currentPage: StateFlow<Int> get() = _currentPage
fun setCurrentPage(currentPage: Int) {
_currentPage.value = currentPage
}
}
MainActivity:
@AndroidEntryPoint
class MainActivity : ComponentActivity(
) {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
CustomTheme {
Surface(color = MaterialTheme.colors.background) {
val sharedPreferences = getSharedPreferences("onBoardingScreen", MODE_PRIVATE)
NavScreen(sharedPreferences)
}
}
}
}
}
@ExperimentalPagerApi
@Composable
fun OnBoardScreen(
navController: NavController,
sharedPreferences: SharedPreferences
) {
val scaffoldState = rememberScaffoldState()
val onBoardViewModel : OnBoardViewModel = viewModel()
val currentPage = onBoardViewModel.currentPage.collectAsState()
val pagerState = rememberPagerState(
pageCount = onBoardItem.size,
initialOffscreenLimit = 2,
initialPage = 0,
infiniteLoop = false
)
Scaffold(
modifier = Modifier.fillMaxSize(),
scaffoldState = scaffoldState
) {
Surface(
modifier = Modifier.fillMaxSize()
) {
if (!sharedPreferences.getBoolean("firstTime", true)) {
navController.navigate("main")
}else{
val editor = sharedPreferences.edit()
editor.putBoolean("firstTime", false)
editor.apply()
}
LaunchedEffect(Unit) {
onBoardViewModel.currentPage
.collect {
pagerState.animateScrollToPage(
page = currentPage.value
)
}
}
Box(
modifier = Modifier
.fillMaxWidth()
.background(
brush = Brush.verticalGradient(
colors = listOf(
white,
grey
)
)
)
) {
Column(
horizontalAlignment = Alignment.CenterHorizontally
) {
HorizontalPager(
state = pagerState
) { page ->
Column(
modifier = Modifier
.padding(top = 60.dp)
.fillMaxWidth(),
horizontalAlignment = Alignment.CenterHorizontally
) {
Text(
text = onBoardItem[page].desc,
modifier = Modifier
.padding(30.dp),
color = custom,
fontSize = 18.sp,
textAlign = TextAlign.Center
)
Spacer(modifier = Modifier.padding(10.dp))
Image(
painter = painterResource(id = onBoardItem[page].image),
contentDescription = "OnBoardImage",
modifier = Modifier
.height(500.dp)
.fillMaxWidth(),
)
}
}
PagerIndicator(onBoardItem.size, pagerState.currentPage)
}
Box(
modifier = Modifier
.align(Alignment.BottomCenter)
) {
Row(
modifier = Modifier
.padding(bottom = 30.dp)
.fillMaxWidth(),
horizontalArrangement = if (pagerState.currentPage != 2 ) {
Arrangement.SpaceBetween
} else {
Arrangement.Center
}
) {
if (pagerState.currentPage == 2) {
CompositionLocalProvider(LocalRippleTheme provides NoRippleTheme) {
Text(
text = "Start",
color = custom,
modifier = Modifier
.padding(start = 280.dp, bottom = 40.dp)
.clickable {
navController.navigate("main")
},
fontSize = 18.sp,
fontWeight = FontWeight.Medium
)
}
} else {
CompositionLocalProvider(LocalRippleTheme provides NoRippleTheme) {
Text(
text = "Skip",
color = custom,
modifier = Modifier
.padding(start = 25.dp, bottom = 42.dp)
.clickable {
navController.navigate("main")
},
fontSize = 18.sp,
fontWeight = FontWeight.Medium
)
}
CompositionLocalProvider(LocalRippleTheme provides NoRippleTheme) {
Text(
text = "Next",
color = custom,
modifier = Modifier
.clickable {
onBoardViewModel.setCurrentPage(pagerState.currentPage 1)
}
.padding(end = 25.dp, bottom = 42.dp),
fontSize = 18.sp,
fontWeight = FontWeight.Medium
)
}
}
}
}
}
}
}
}
@Composable
fun PagerIndicator(size: Int, currentPage: Int) {
Row(
horizontalArrangement = Arrangement.SpaceBetween,
modifier = Modifier.padding(top = 40.dp)
) {
repeat(size) {
IndicateIcon(
isSelected = it == currentPage
)
}
}
}
@Composable
fun IndicateIcon(isSelected: Boolean) {
val width = animateDpAsState(
targetValue = if (isSelected) 10.dp else 10.dp
)
Box(
modifier = Modifier
.padding(2.dp)
.height(10.dp)
.width(width.value)
.clip(CircleShape)
.background(
if (isSelected) custom else customColor
)
)
}
CodePudding user response：
I think the problem is that you are calling navController.navigate("main") during composition while not ensuring that it is called only once when the navigation should happen, thus creating a situation where navController.navigate("main") is called repeatedly in quick succession. I think that might be the cause and the exception might be the effect.
Wrap the navigation call (that is now directly part of the composition) into a LaunchedEffect
if (!sharedPreferences.getBoolean("firstTime", true)) {
LaunchedEffect(Unit) {
navController.navigate("main")
}
} else {
val editor = sharedPreferences.edit()
editor.putBoolean("firstTime", false)
editor.apply()
}