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VisualizaçõesType 'State<List<User>?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate
I'm trying to get a value from LiveData with observeAsState in jetpack compose, but I get a weird error
Type 'State<List?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate
Code
@Composable
fun UserScreen(userViewModel:UserViewModel){
val items: List<User> by userViewModel.fetchUserList.observeAsState()
UserList(userList = items)
}
ViewModel
class UserViewModel: ViewModel() {
private val dataSource = UserDataSource()
val fetchUserList = liveData {
emit(dataSource.dummyUserList)
}
}
8 Respostas
Responde à pergunta0
You need to import
import androidx.compose.runtime.getValue
which will import this function which is basically by
inline operator fun <T> State<T>.getValue(thisObj: Any?, property: KProperty<*>): T = value
0
You could use: import androidx.compose.runtime.*
Necessary imports are:
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.runtime.getValue
import androidx.compose.runtime.setValue
import androidx.compose.runtime.mutableStateOf
var value by remember { mutableStateOf("") }
0
I had this problem despite imports! Took a bit but then I realised where my problem was the variable for whatever you're observing needs to be a val not a var:
In my case it was
var background: Int by currentBackgroundColor.observeAsState(0)
Should have been:
val background: Int by currentBackgroundColor.observeAsState(0)
0
Adding a dependency fixed the problem for me:
implementation "androidx.compose.runtime:runtime:$compose_version"
Thanks to Tayaab Mizhar
0
To fix the error add the following imports:
// for a 'val' variable
import androidx.compose.runtime.getValue
// for a `var` variable also add
import androidx.compose.runtime.setValue
// or just
import androidx.compose.runtime.*
To use a variable as a property delegate you should provide getValue operator function for read-only val variables and getValue and setValue functions for var variables.
To read more about how property delegates and state are combined in jetpack compose see Use remember to create internal state in a composable documentation section. There's also an explanation in Thinking in Compose video.
0
In my case, in a compose application it was this missing import that provoc the error
import androidx.compose.getValue
0
I think type of items must be nullable since you observing LiveData:
val items: List<User>? by userViewModel.fetchUserList.observeAsState()
0
If you get a compiler error that observeAsState or getValue are not defined make sure you have the following imports:
import androidx.compose.runtime.getValue
import androidx.compose.runtime.livedata.observeAsState
This information is from Step #4 in the "Using State in Jetpack Compose" codelab.