具有 ViewModel 参数时不显示 Jetpack Compose Preview-解网

问：

我正在使用 Jetpack Compose，但注意到预览未显示。我读过这样的文章，但似乎我的问题有不同的根本原因。即使我为compose函数中的所有参数添加了默认值，如下所示：

@OptIn(ExperimentalLifecycleComposeApi::class)
@Composable
@ExperimentalFoundationApi
@Preview
fun VolumeSettingsScreen(
    speech: SpeechHelper = SpeechHelper(), // my class that converts text to speech
    viewModel: VolumeSettingsViewModel = hiltViewModel(), // using Hilt to inject ViewModels
    navController: NavHostController = rememberNavController() // Compose Navigation component
) {
    MyAppheme {
        Box(
             ...
        )
    }
}

当我回滚一些更改时，我意识到无论它们是否注入了 Hilt，它都不支持。@PreviewviewModels

知道如何解决这个问题吗？

Android Kotlin android-jetpack-compose android-jetpack-compose-preview

@OptIn(ExperimentalLifecycleComposeApi::class)
@Composable
@ExperimentalFoundationApi
@Preview
fun VolumeSettingsScreen(
    modifier: Modifier = Modifier,
    speechCallbacks: SpeechCallbacks = SpeechCallbacks(),
    navigationCallbacks: NavigationCallbacks = NavigationCallbacks(),
    viewModelCallbacks: VolumeSettingsScreenCallbacks = VolumeSettingsScreenCallbacks()
) {
    MyAppheme {
        Box(
             ...
        )
    }
}

我没有直接在 compose 中传递 ViewModel，而是在 Data 类中传递了所需的函数，例如，如下所示：

data class VolumeSettingsScreenCallbacks(
    val uiState: Flow<BaseUiState?> = flowOf(null),
    val onValueUpSelected: () -> Boolean = { false },
    val onValueDownSelected: () -> Boolean = { false },
    val doOnBoarding: (String) -> Unit = {},
    val onScreenCloseRequest: (String) -> Unit = {} 
)

我制作了一个在 ViewModel 中生成这些回调的方法，如下所示：

@HiltViewModel
class VolumeSettingsViewModel @Inject constructor() : BaseViewModel() {

    fun createViewModelCallbacks(): VolumeSettingsScreenCallbacks =
        VolumeSettingsScreenCallbacks(
            uiState = uiState,
            onValueUpSelected = ::onValueUpSelected,
            onValueDownSelected = ::onValueDownSelected,
            doOnBoarding = ::doOnBoarding,
            onScreenCloseRequest = ::onScreenCloseRequest
        )

 ....
}

在 NavHost 中，我像这样提升了 ViewModel 的创建：

    @Composable
    @ExperimentalFoundationApi
    fun MyAppNavHost(
        speech: SpeechHelper,
        navController: NavHostController,
        startDestination: String = HOME.route,
    ): Unit = NavHost(
        navController = navController,
        startDestination = startDestination,
    ) {
        ...
    
        composable(route = Destination.VOLUME_SETTINGS.route) {
            hiltViewModel<VolumeSettingsViewModel>().run {
                VolumeSettingsScreen(
                    modifier = keyEventModifier,
                    speechCallbacks = speech.createCallback() // my function,
                    navigation callbacks = navController.createCallbacks(), //it is mine extension function                  
                    viewModelCallbacks = createViewModelCallbacks()
                )
            }
        }
    
        ...
    }

这有点复杂，但:D有效。如果有一些彗星需要改进，我会很高兴。

4赞 z.g.y 11/20/2022 #2

你有没有考虑过有一个结构，你有一个和实际分开的，像这样？ScreenContent

// data class
data class AccountData(val accountInfo: Any?)

// composable "Screen", where you define contexts, viewModels, hoisted states, etc
@Composable
fun AccountScreen(viewModel: AccountViewModel = hiltViewModel()) {

    val accountData = viewModel.accountDataState.collectAsState()

    AccountContent(accountData = accountData) {
        // click callback
    }
}

//your actual composable that hosts your child composable widget/components
@Composable
fun AccountContent(
    accountData: AccountData,
    clickCallback: () ->
) {
   ...
}

在哪里可以预览这样的内容？Content

@Preview
@Composable
fun AccountContentPreview() {

    // create some mock AccountData
    val mockData = AccountData(…)
    AccountContent(accountData = mockData) {
         // I'm not expecting some actual ViewModel calls here, instead I'll just manipulate the mock data
    }
}

这样一来，实际内容可组合项不需要配置的所有组件都将分开，从而免去配置预览的麻烦。

只是一个附加的注释，可能偏离主题，我刚刚注意到你有一个这样的参数，

speech: SpeechHelper = SpeechHelper()

您可以考虑使用 compositionLocalProvider（如果需要），它可以清理您的参数。

具有 ViewModel 参数时不显示 Jetpack Compose Preview

Jetpack Compose Preview is not showing when having a ViewModel parameter

评论

评论