键入“状态<列表<用户>?>"没有方法"getValue(Nothing ?, KProperty< *>))"，因此它不能充当委托 [英] Type 'State<List<User>?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate

问题描述

我正在尝试在jetpack中使用observeAsState从LiveData中获取一个值，但出现一个奇怪的错误

I'm trying to get a value from LiveData with observeAsState in jetpack compose, but I get a weird error

键入状态<列表?>"没有方法'getValue(Nothing ?, KProperty< *>))，因此它不能充当代理人

Type 'State<List?>' has no method 'getValue(Nothing?, KProperty<*>)' and thus it cannot serve as a delegate

代码

@Composable
fun UserScreen(userViewModel:UserViewModel){
    val items: List<User> by userViewModel.fetchUserList.observeAsState()
    UserList(userList = items)
}

class UserViewModel: ViewModel() {

    private val dataSource = UserDataSource()
    val fetchUserList = liveData {
        emit(dataSource.dummyUserList)
    }
}

推荐答案

如果遇到未定义observeAsState或getValue的编译器错误，请确保您具有以下导入:

If you get a compiler error that observeAsState or getValue are not defined make sure you have the following imports:

导入androidx.compose.runtime.getValue

import androidx.compose.runtime.getValue

导入androidx.compose.runtime.livedata.observeAsState

import androidx.compose.runtime.livedata.observeAsState

该信息来自步骤4中的"Jetpack Compose中的使用状态".代码实验室.

This information is from Step #4 in the "Using State in Jetpack Compose" codelab.

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