如何更新ViewModel中的StateFlow

Question

我的可组合项中有此员工列表：

val employeeViewModel: EmployeeViewModel = viewModel()
val employeeState by employeeViewModel.employeeState.collectAsState(ViewResult.Loading)

ALlEmployees(employeeState = employeeState,
      onRefresh = {
         // TODO: Re-fetch the list
      })

这是我的视图模型

var employeeState: StateFlow<ViewResult<List<Employee>>> = fetchEmployeesUseCase().stateIn(
            scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(5_000),
            initialValue = ViewResult.Loading,
        )
private set

我真的不知道如何重新获取员工列表。该流程需要以某种方式重新触发。如有任何帮助，我们将不胜感激。

Answer 1

为了实现这一目标，我们首先要重构 viewModel。 我一贯的处理方式是这样的：

class EmployeeViewModel(
    private val repository: TestRepository
) : ViewModel() {

    // Here we store the value of the employee list status
    // We have the internal mutable state '_uiEmployeeState' and the public state 'uiEmployeeState'
    // The public state will be used in the composable to obtain the state value safely
    private val uiEmployeeState = MutableStateFlow<ViewResult<List<Employee>>>(ViewResult.Loading)
    val _uiEmployeeState: StateFlow<ViewResult<List<Employee>>> = uiEmployeeState

    // Use this function if you want the state to be updated every time the viewmodel is instantiated.
    init {
        fetchEmployees()
    }

    /**
     * Function that is responsible for updating the employee state
     *  - Use a 'viewModelScope' if the function is suspend, otherwise do it directly
     *  - Use 'update' to update the state value, you can also use '.value'
     *  - Use 'first' to get the first value of the flow and update the state
     */
    fun fetchEmployees() {
        uiEmployeeState.value = ViewResult.Loading
        viewModelScope.launch {
            uiEmployeeState.update {
                repository.fetchEmployeesUseCase().first()
            }
        }
    }

}

在viewModel内部的

fetchEmployees()

中，您可以将状态临时设置为

loading

，以防万一您有一些动画或类似的东西，否则您可以忽略它并直接更新状态。 另外，在我的示例中，我们从存储库获取数据，您可以将其更改为您的用例

在用户界面方面，它会是这样的：

val employeeViewModel: EmployeeViewModel = viewModel()
// You do not need to give it the initial value since the viewModel already has one
val employeeState by employeeViewModel._uiEmployeeState.collectAsState()

AllEmployees(
    employeeState = employeeState,
    onRefresh = { employeeViewModel.fetchEmployees() }
     // You can also use it as a lambda reference
    //onRefresh = employeeViewModel::fetchEmployees

)

另外，当您从 viewModel 听到状态时，您可以检查推荐的库：

->

collectAsStateWithLifecycle()

它仅以生命周期感知的方式从 Flow 或 StateFLow 收集值，从而允许您的应用程序节省不需要的应用程序资源。特别适用于您使用 StateFlow 的情况

我给你一个参考链接： https://developer.android.com/jetpack/compose/state?hl=es-419#use-other-types-of-state-in-jetpack-compose