Android collectAsStateWithLifecycle()未在可组合的内部收集

xqk2d5yq  于 2022-11-27  发布在  Android
关注(0)|答案(1)|浏览(197)

我使用compose LazyColumn with viewModel更新列表项,方法是在viewModel中包含:

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()函数就可以更新stateFlow,并且我应该在MainActivity内的可组合函数中收集collectAsStateWithLifecycle()的联系人列表

@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))
                    }
                }
                 ...

其中,contactsListViewModel声明在我使用hilt注入的Activity之上:

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

由于某种原因,uiState.contacts在可组合函数中是空的,但是当我在viewModel函数中记录它时,它确实包含了项,因此我的列表保持为空。
有什么建议吗?
谢谢

q3qa4bjr

q3qa4bjr1#

请使用SnapshotStatelist/(mutableStateListOf())代替普通列表(mutableList)。

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

也请检查这个post这个和这个

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