我正在使用Jetpack Compose与导航组件，Retrofit和Paging 3。我遇到的问题是，当我导航到具有分页的屏幕时，它会发出3个连续的网络请求，当我导航到另一个屏幕时，它会再次发出请求，因此，它不会缓存。从性能Angular 来看，这不太好。我尝试在composable中使用LauncdedEffect，但它抛出了一个编译错误。我可以做些什么来防止这种多个请求？

我的viewModel：

class CoursesViewModel(private val courseDataRepository: CourseDataRepository): ViewModel() {
    // ......
    fun getCourses(primaryCategory: String): Flow<PagingData<CourseData>> =
        courseDataRepository.getCourses(primaryCategory).cachedIn(viewModelScope)
    // ......
}

我的仓库：

interface CourseDataRepository {
    // ....
     fun getCourses(queryParam: String): Flow<PagingData<CourseData>>
    // ....
}

 class DefaultCourseDataRepository(private val retrofitService: EskoolApiService): CourseDataRepository { 
    // .....
      override fun getCourses(queryParam: String): Flow<PagingData<CourseData>> {
         return Pager(
             config = PagingConfig(pageSize = PAGE_SIZE),
             pagingSourceFactory = {
                 CourseDataSource(queryParam, retrofitService)
             }
         ).flow
     }
    // .....
}

我的数据源：

class CourseDataSource(
    private val queryIdentifier: String,
    private val apiService: EskoolApiService
): PagingSource<Int, CourseData>() {

    override fun getRefreshKey(state: PagingState<Int, CourseData>): Int? {
        return state.anchorPosition?.let { anchorPosition ->
            state.closestPageToPosition(anchorPosition)?.prevKey?.plus(1)
                ?: state.closestPageToPosition(anchorPosition)?.nextKey?.minus(1)
        }
    }

    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, CourseData> {

        return try {
            val nextPage = params.key ?: 1
            val filters = mapOf("page" to nextPage, "page_size" to PAGE_SIZE)

            val data: Courses = if (queryIdentifier == defaultCoursesArg) {
                            apiService.getAllCourses(filters, null)
                        } else {
                            apiService.getAllCourses(filters, queryIdentifier)
                        }

            LoadResult.Page(
                data = data.courses,
                prevKey = if (nextPage == 1) null else nextPage - 1,
                nextKey = if (data.courses.isEmpty()) null else nextPage + 1
            )
        } catch (e: IOException) { // ************
            return LoadResult.Error(e)
            } catch (exception: HttpException) {
                return LoadResult.Error(exception)
            }
        }
}

CoursesScreen

@SuppressLint("MutableCollectionMutableState")
@Composable
fun CoursesScreen(
    modifier: Modifier = Modifier,
    coursesViewModel: CoursesViewModel,
    coursesParam: String? = defaultCoursesArg,
    onClickCourseDetailsBySpan: (Int) -> Unit = {},
    onClickCourseDetailsByTitle: (Int) -> Unit = {},
) {

    val courseItems: LazyPagingItems<CourseData> =
        coursesViewModel.getCourses(coursesParam!!).collectAsLazyPagingItems()

    Surface(
        modifier = modifier
            .padding(vertical = CARD_PADDING),
        color = colors.background
    ) {
        CourseCards(
            courses = courseItems,
            onClickCourseDetailsBySpan = onClickCourseDetailsBySpan,
            onClickCourseTitle = onClickCourseDetailsByTitle,
        )
    }
}

主活动

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            val coursesViewModel: CoursesViewModel = viewModel(factory = CoursesViewModel.Factory)
            // app content
            ESchoolApp(viewModel = coursesViewModel)
        }
    }
}