AndroidcollectAsStateWithLifecycle() 未在可组合项内收集

Question

我正在使用 composeLazyColumn和 viewModel 通过在我的 viewModel 中更新列表项：

    data class ContactsListUiState(
       val contacts: MutableList<Contact>
    )
    @HiltViewModel
    class ContactsViewModel @Inject constructor(savedStateHandle: SavedStateHandle) : ViewModel() {
    private val _contactsListUiState = MutableStateFlow(ContactsListUiState(mutableListOf()))
    val contactsListUiState: StateFlow<ContactsListUiState> = _contactsListUiState.asStateFlow()

    private fun updateContactsList(newContacts: MutableList<Contact>) {
        _contactsListUiState.update{ currentState ->
            currentState.copy(
                contacts = newContacts
            )
        }
    }

这样我的updateContactsList()函数就会更新 stateFlow，并且我应该在collectAsStateWithLifecycle()可组合函数内部收集联系人列表MainActivity

@OptIn(ExperimentalLifecycleComposeApi::class, ExperimentalFoundationApi::class)
    @Composable
    fun ContactsListScreen(
        navController: NavController,
        modifier: Modifier = Modifier
    ) {
        Log.d("ViewModel", "ContactsListScreen recomposed")
        val uiState by contactsViewModel.contactsListUiState.collectAsStateWithLifecycle()
        Box(modifier = modifier) {
            val listState = rememberLazyListState()
            val scope = rememberCoroutineScope()
            Column {
                TextField(
                    value = searchText,
                    singleLine = true,
                    onValueChange = {
                        searchText = it
                        Log.d("MainActivity", "calling filter with $it")
                        contactsViewModel.filterContactsByString(it)
                    },
                    leadingIcon = if (searchText.isNotBlank()) searchLeadingIcon else null,
                    trailingIcon = if (searchText.isBlank()) searchTrailingIcon else null,
                    modifier = Modifier
                        .fillMaxWidth()
                        .background(Color.White)
                )
                LazyColumn(
                    Modifier.fillMaxWidth(),
                    state = listState,
                    contentPadding = PaddingValues(bottom = 80.dp)
                ) {                      
                        items(uiState.contacts) { contact ->
                            ContactListItem(
                                navController,
                                contact = contact,
                                modifier = Modifier.fillMaxWidth()
                            )
                            Divider(thickness = 0.5.dp, color = colorResource(id = R.color.blue))
                    }
                }
                 ...

wherecontactsListViewModel是在我使用 hilt 注入的活动之上声明的：

@AndroidEntryPoint
class MainActivity : ComponentActivity(), LoaderManager.LoaderCallbacks<Cursor> {
    private val contactsViewModel: ContactsViewModel by viewModels()

由于某种原因uiState.contacts，可组合函数内为空，但当我将其记录在 viewModel 函数内时，它确实包含项目，因此我的列表保持为空。

关于可能出什么问题有什么建议吗？

谢谢

Answer 1

请使用SnapshotStatelist/( mutableStateListOf()) 而不是普通列表 ( mutableList)。

private val _contactsListUiState = MutableStateFlow(ContactsListUiState(mutableStateListOf()))

另请检查这篇文章这个和这个