android - Jetpack Compose – 我需要使用哪个依赖项才能使用状态委托(delegate)？

Question

代码实验室中提供的示例存在编译时错误。

这是 View 模型

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
}

但它会产生以下错误:

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

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) { … }
}

我需要引入什么依赖项才能使委托(delegate)工作？

这是我的依赖项: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 doc 中所述，尝试添加以下导入:

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