Jetpack组合-我需要使用哪个依赖项才能使用状态委托？

Question

我在代码实验室提供的样本中有一个编译时错误。

这是ViewModel

class VM : ViewModel() {
     val isVisible = MutableStateFlow(true).asStateFlow()
}

这就是我想写的：

@Composable
fun Whatever(vm: VM = viewModel()) {
    val isVisible by vm.isVisible.collectAsState(true)
    // Use is visible here
}

但是，它会产生以下错误：

键入'State‘没有方法'getValue(Nothing?，KProperty<*>)’，因此它不能充当委托。

这真的很奇怪，因为我可以这样使用它：

@Composable
fun Whatever(vm: VM = viewModel()) {
    val isVisible = vm.isVisible.collectAsState(true)
    if(isVisible.value) { … }
}

我需要引入什么样的依赖性才能使委托工作？

下面是我的依赖关系:和compose_version = 1.0.0-beta01

dependencies {
    // LiveData
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.3.0"
    implementation 'androidx.core:core-ktx:1.3.2'
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'

    implementation "androidx.activity:activity-compose:1.3.0-alpha03"
    implementation "androidx.compose.runtime:runtime:$compose_version"
    implementation "androidx.compose.ui:ui:$compose_version"
    implementation "androidx.compose.foundation:foundation-layout:$compose_version"
    implementation "androidx.compose.material:material:$compose_version"
    implementation "androidx.compose.material:material-icons-extended:$compose_version"
    implementation "androidx.compose.foundation:foundation:$compose_version"
    implementation "androidx.compose.animation:animation:$compose_version"
    implementation "androidx.compose.ui:ui-tooling:$compose_version"
    implementation "androidx.compose.runtime:runtime-livedata:$compose_version"
    implementation "androidx.compose.runtime:runtime:$compose_version"
    implementation "androidx.compose.ui:ui:$compose_version"
    implementation "androidx.compose.ui:ui-tooling:$compose_version"

    implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.3.0'

    // Kotlin coroutines
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines_version"

    implementation 'androidx.appcompat:appcompat:1.3.0-beta01'
    implementation 'androidx.activity:activity-ktx:1.2.0'
    implementation 'androidx.core:core-ktx:1.5.0-beta02'
    implementation "androidx.activity:activity-compose:1.3.0-alpha03"

    implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:2.3.0"
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.3.0"
    implementation "androidx.lifecycle:lifecycle-viewmodel-compose:1.0.0-alpha02"

    androidTestImplementation 'androidx.test:rules:1.3.0'
    androidTestImplementation 'androidx.test:runner:1.3.0'
    androidTestImplementation "androidx.compose.ui:ui-test:$compose_version"
    androidTestImplementation "androidx.compose.ui:ui-test-junit4:$compose_version"
}

Answer 1

如文档中所述，尝试添加以下导入：

import androidx.compose.runtime.getValue
import androidx.compose.runtime.livedata.observeAsState