im currently experiencing with jetpack compose states.
Check out this composable:
@Composable
fun CounterWithoutRemember(reset: MutableState<Boolean>) {
val count = mutableStateOf(0)
Box(Modifier.fillMaxWidth()) {
Column {
Text("Your count: ${count.value}")
ElevatedButton(onClick = {
count.value += 1
}) {
Text("Add 1")
}
}
}
}
This is working as expected. count is state without remember, that makes it resetting to 0 after recomposition.
But this code :
@Composable
fun CounterWithoutRemember(reset: MutableState<Boolean>) {
val count = mutableStateOf(0)
Surface(Modifier.fillMaxWidth()) {
Column {
Text("Your count: ${count.value}")
ElevatedButton(onClick = {
count.value += 1
}) {
Text("Add 1")
}
}
}
}
I change the Box with Surface. with this code, i see that the count state is persisting like when i use remember when that composable recomposes. Can anyone explain me?
this is the activity :
class MainActivity : ComponentActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val resetState = mutableStateOf(false)
setContent {
MyApplicationTheme {
// A surface container using the 'background' color from the theme
Surface(Modifier.padding(52.dp)) {
Column {
Counter()
CounterWithRemember(resetState)
CounterWithoutRemember(resetState)
ElevatedButton(onClick = {
resetState.value = !resetState.value
}) {
Text(text = "Reset")
}
}
}
}
}
}
}
>Solution :
Because Column, Row, and Box are inline functions and they don’t create a scope. But Surface creates a scope as any other Composable that is not inline and returns Unit that limits composition range. Because of that CounterWithoutRemember is not recomposed.
@Composable
fun CounterWithoutRemember(reset: MutableState<Boolean>) {
val count = mutableStateOf(0)
Surface(Modifier.fillMaxWidth()) {
Column {
Text("Your count: ${count.value}")
ElevatedButton(onClick = {
count.value += 1
}) {
Text("Add 1")
}
}
}
}
Why does mutableStateOf without remember work sometimes?