房间流总是返回kotlinx.coroutines.flow.SafeFlow@c8abe2e

Question

最初，我从网络中获取列表数据，并将其存储在数据库中。

这是一对多的关系。为此，我创建了两个表和一个关系数据类。

产品表：

@Entity(tableName = "Product")
data class Products (

    @PrimaryKey(autoGenerate = false)
    @ColumnInfo(name = "id")
    var id : Int = 0,

    @ColumnInfo(name = "name")
    var name  : String? = null,

    @ColumnInfo(name = "category_id")
    var category_id : String? = null,

    @ColumnInfo(name = "subcategory_id")
    var subcategory_id : String? = null,

    @ColumnInfo(name = "variants")
    var variants : List<Variants> = listOf()
)

变式表：

@Entity(tableName = "Variant")
data class Variants (

    @PrimaryKey(autoGenerate = false)
    @ColumnInfo(name = "id")
    var id : Int  = 0,

    @ColumnInfo(name = "product_id", index = true)
    var product_id : Int?  = null,

    @ColumnInfo(name = "measurement")
    var measurement : String?  = null,

    @ColumnInfo(name = "price")
    var price : String?  = null
)

带有变体的产品(两个表之间的关系)

  data class ProductWithVariants(
    @Embedded val product: Products,
    @Relation(
        parentColumn = "id",
        entityColumn = "product_id"
    )
    val variants: MutableList<Variants> 
)

Dao :我使用查询获取ProductsWithVariants数据，并通过subcategory_id进行筛选。

@Transaction
@Query("SELECT * FROM Product WHERE subcategory_id=:subcat")
fun getProductWithVariants(subcat:Int): Flow<MutableList<ProductWithVariants>>

ViewModel：

var productListN: Flow<MutableList<ProductWithVariants>> = flowOf(mutableListOf())

fun networkproductlist() = viewModelScope.launch(Dispatchers.IO) {
    productist.collectLatest {
        when (it) {
            Resource.Empty -> {
                Log.e("product", "" + "empty")
            }
            is Resource.Failure -> {
                Log.e("product", "" + "failure")
            }
            Resource.Loading -> {

            }
            is Resource.Success -> {
                val response = it.value
                for (i in 0 until response.data.size) {
                    val product: Products = response.data.get(i)
                    for (j in 0 until product.variants.size) {
                        variants = product.variants.get(j)
                    }
                }
                productsDao.deleteAllProducts()
                productsDao.insertProducts(response.data)
                productsDao.insertVariants(variants!!)
                val subcategoryid = SubCategoryList(response.data[0].subcategory_id!!.toInt())
                productsDao.insertSubCat(subcategoryid)
                productListN = productsDao.getProductWithVariants(response.data[0].subcategory_id!!.toInt())
                Log.e("product","product in room viewmodel : $productListN")
            }
        }
    }
}

如前所述，获得了成功资源中的网络响应，并在相应的表中插入产品和变体，然后在数据库中插入产品子类别，然后按下一行的ProductWithVariants ()获得getProductWithVariants()列表。

现在的问题是-我总是得到kotlinx.coroutines.flow.SafeFlow@f06e8a9作为productlistN的响应。

主要活动：

lifecycleScope.launch(Dispatchers.Main) {
    proadapter = ProductAdapter()
    binding.ProductRecyclerView.apply {
       adapter = proadapter
    }
}

lifecycleScope.launch(Dispatchers.Main) {
    viewModel.productListN.collect {
        println("Received UserInfo List $it")
        proadapter.setMutableArraylist(it)
        proadapter.notifyDataSetChanged()
    }
}

Answer 1

我在您的代码中发现了几个问题：

在

• In ViewModel中使用var productListN = ...，然后用新的对象productListN = productsDao.getProductWithVariants(response.data[0].subcategory_id!!.toInt())重新初始化它。您不应该重新初始化它，您必须使用相同的对象。您可以尝试使用StateFlow或SharedFlow来发出数据：

val productListN: Flow<MutableList<ProductWithVariants>> = StateFlow(mutableListOf())
...
productListN.value = ...

在lifecycleScope.launch { ... }函数之外，

• 在Activity中初始化proadapter和binding.ProductRecyclerView，而为了收集Flow数据，只需使用launch

proadapter = ProductAdapter()
binding.ProductRecyclerView.apply {
    adapter = proadapter
}

lifecycleScope.launch {
    viewModel.productListN.collect {
        println("Received UserInfo List $it")
        proadapter.setMutableArraylist(it)
        proadapter.notifyDataSetChanged()
    }
}