Jetpack Compose collectAsState() 不适用于 Flow combine()

Question

我想从 Firestore 加载数据，并使用 Flow 将其与其他数据合并 combine()

视图模型：

private val userCurrentProject = MutableStateFlow("")

val projects = repository
        .listenToProject() //listening via Firestore snapshot listener, no problem here
        .combine(userCurrentProject) { projects, currentProjectName -> 
            // combine works and called normally
            projects.map { project ->
                project.apply {
                    isUserCurrentProject = name == currentProjectName
                }
            }
        }

fun setCurrentProject(projectName: String) = viewModelScope.launch {
    userCurrentProject.emit(projectName)
}

可组合项：

fun ProjectListScreen(navController: NavHostController, viewModel: ProjectsViewModel) {
    val projects by viewModel.projects.collectAsState(initial = emptyList())

    // This is where the problem started
    // Lazy column not updated when projects flow is emitting new value
    // Even Timber log does not called
    Timber.d("Projects : $projects")
    LazyColumn {
            items(projects) { project ->
                ProjectItem(project = project) {
                    currentlySelectedProject = project
                    scope.launch { bottomSheetState.show() }
                }
            }
    }

flow正常，但是state一直没有更新，不知道为什么。也许这是 collectAsState() 的问题？

但是当我导航到下一个屏幕（添加新项目屏幕）然后按返回键 (popBackStack) 时状态会更新

注意：使用 asLiveData() 和 observeAsState() 也不起作用。

Answer 1

我终于找到了答案

罪魁祸首是 custom object/class 的状态与 primitives (String, Int,等等）

对于状态对象，你需要使用copy()

所以我只是更改了 ViewModel 的这一部分

val projects = repository
        .listenProject()
        .combine(userCurrentProject) { projects, currentProjectName ->
            projects.map { project ->
                // use copy instead of apply
                val isCurrentProject = project.name == currentProjectName
                project.copy(isUserCurrentProject = isCurrentProject)
            }
        }

Jetpack Compose collectAsState() 不适用于 Flow combine()

Jetpack Compose collectAsState() does not work with Flow combine()

android-jetpack-compose

kotlin-flow