[英]Jetpack Compose Preview is not showing when having a ViewModel parameter
我正在使用 Jetpack Compose 並注意到未顯示預覽。 我讀過這樣的文章,但我的問題似乎有不同的根本原因。 甚至我在 compose function 中為所有參數添加了默認值,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(
...
)
}
}
當我回滾一些更改時,我意識到@Preview
不支持viewModels
,無論它們是否注入了 Hilt。
知道如何解決這個問題嗎?
我設法通過將 ViewModel 的函數包裝到數據類中來可視化屏幕預覽,如下所示:
@OptIn(ExperimentalLifecycleComposeApi::class)
@Composable
@ExperimentalFoundationApi
@Preview
fun VolumeSettingsScreen(
modifier: Modifier = Modifier,
speechCallbacks: SpeechCallbacks = SpeechCallbacks(),
navigationCallbacks: NavigationCallbacks = NavigationCallbacks(),
viewModelCallbacks: VolumeSettingsScreenCallbacks = VolumeSettingsScreenCallbacks()
) {
MyAppheme {
Box(
...
)
}
}
我沒有直接在 compose 中傳遞 ViewModel,而是需要數據 class 中的函數,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 = {}
)
我創建了一個在 ViewModel 中生成這些回調的方法,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,我像這樣提升了 ViewModel 的創建:
@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()
)
}
}
...
}
它有點復雜,但它有效:D。 如果有一些彗星需要改進,我會很高興。
你有沒有考慮過有一個結構,你有一個Screen
和實際的Content
這樣分開?
// 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: () ->
) {
...
}
在哪里可以預覽這樣的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
}
}
這樣,實際可組合內容不需要配置的所有組件都被分開,讓您從配置預覽的麻煩中解脫出來。
只是一個補充說明,可能是題外話,我只是注意到你有一個這樣的參數,
speech: SpeechHelper = SpeechHelper()
您可能會考慮使用compositionLocalProvider (如果需要),它可以清理您的參數。
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