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我有一个用 Compose 制作的非常简单的应用程序 ui。

目前有 3 个屏幕：登录、项目列表和项目详细信息。

问题是当我单击项目列表中的项目时，我导航到项目详细信息并将项目 ID 作为导航 arg 传递。

问题是，我无法检索它并且参数包是空的。

这是我的代码：

MainActivity：

@AndroidEntryPoint
class MainActivity : ComponentActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            AdrestoApplication()
        }
    }
}

主要可组合：

@Composable
fun AdrestoApplication() {
    val authViewModel = hiltViewModel<AuthViewModel>()

    val navController = rememberNavController()
    val navBackStackEntry by navController.currentBackStackEntryAsState()
    val isLoggedIn = authViewModel.isLoggedIn()
    val initialRoute =
        if (isLoggedIn) Destinations.LISTINGS_LIST else Destinations.LOGIN_ROUTE
    val currentRoute = navBackStackEntry?.destination?.route ?: initialRoute

    AdrestoTheme {
        NavGraph(
            navController = navController,
            startDestination = currentRoute,
        )
    }
}

NavGraph：

object Destinations {
    const val LOGIN_ROUTE = "login"
    const val HOME_ROUTE = "home"
    const val ORDER_DETAILS = "order_details"
    const val ORDERS_LIST = "orders_list"
    const val LISTING_DETAILS = "listing_details/{listingId}"
    const val LISTINGS_LIST = "listings_list"
}

@Composable
fun NavGraph(
    navController: NavHostController = rememberNavController(),
    startDestination: String = Destinations.LOGIN_ROUTE,
) {
    NavHost(navController = navController, startDestination = startDestination) {
        composable(Destinations.LOGIN_ROUTE) {
            Login(
                navController = navController,
            )
        }
        composable(Destinations.LISTINGS_LIST) {
            ListingsScreen(
                navController = navController,
            )
        }
        composable(
            Destinations.LISTING_DETAILS,
            arguments = listOf(navArgument("listingId") { type = NavType.LongType })
        ) {
            Log.d("Navhost","NavGraph: the nav arg found is: ${it.arguments!!.getLong("listingId")}") // logs 0
            ListingScreen(
                navController = navController,
                listingId = it.arguments!!.getLong("listingId"),
            )
        }
    }
}

使用参数触发导航的 UI 部分：

LazyColumn(
    modifier = Modifier
        .padding(all = 8.dp)
        .background(MaterialTheme.colors.background)
) {
    items(listings.value.data ?: listOf()) { listing ->
        Listing(
            listing = listing,
            onCardClick = {
                Log.d("some tag", "ListingsScreen: navigating to ${listing.id}") // logs as expected
                val route = "listing_details/${listing.id}"
                Log.d("some tag", "ListingsScreen: the route is $route") //logs listing_details/418 (for example)
                navController.navigate(route)
            },
        )
    }
}

我不明白这里出了什么问题，不是同一个导航图中的可组合物吗？

我还有另一个问题，当我按下后退按钮时，导航不会上去但它会关闭应用程序（就像没有后退堆栈......）。

4

1 回答 1

0

问题出在 的起始目标参数中NavGraph，每次导航到新屏幕时，我都会（不知不觉地）重新初始化 navController 后台堆栈。

@Composable
fun AdrestoApplication() {
    val authViewModel = hiltViewModel<AuthViewModel>()

    val navController = rememberNavController()
    val navBackStackEntry by navController.currentBackStackEntryAsState()
    val isLoggedIn = authViewModel.isLoggedIn()
    val initialRoute =
        if (isLoggedIn) Destinations.LISTINGS_LIST else Destinations.LOGIN_ROUTE
    val currentRoute = navBackStackEntry?.destination?.route ?: initialRoute

    AdrestoTheme {
        NavGraph(
            navController = navController,
            startDestination = currentRoute, // this was issue, changed to a static initial route.
        )
    }
}
于 2022-02-03T08:42:38.147 回答