RecyclerView项未使用LiveData更新

Question

我有一个使用数据绑定，实时数据，房间，kotlin koroutine，视图模型，导航组件和匕首的应用程序。我有一个活动，有两个片段。

ListFragment：在回收站视图中显示项目列表。

DetalFragment：显示项目详细信息，并可以使用保存按钮更新项目的某些字段。

问题是，当我从detailfragment更新某些字段时，更改在listfragment中不可见，但是当我上下滚动时，更改变为可见。

ListFragment：

 @Inject
lateinit var viewModelFactory: ViewModelProvider.Factory
val viewModel: ListViewModel by viewModels {
    viewModelFactory
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    val bindings = ListFragmentBinding.inflate(inflater, container, false).apply {
        viewmodel = viewModel
    }
    bindings.lifecycleOwner = this
    adapter = ItemsAdapter()
    bindings.recyclerView.adapter = adapter
    viewModel.items.observe(
        viewLifecycleOwner,
        Observer { adapter.submitList(it)})
    return bindings.root
}

ListViewModel：

var items: LiveData<PagedList<Item>> = repository.items

存储库：

val items<PagedList<Item>>
get()=itemDao.getAllItemsPaged().toLiveData(pageSize=50)
fun getItemFlow(id: String): Flow<Item> = itemDao.getItemFlow(id)
suspend fun updateItem(item: Item) {
   itemDao.updateItem(item)
}

ItemDao：

 @Query("SELECT * FROM item")
fun getAllItemsPaged(): DataSource.Factory<Int,Item>
@Query("SELECT * FROM itemWHERE id=:id")
fun getItemFlow(id:String):Flow<Item>
@Update
suspend fun updateItem(item:Item)

ItemFragment：

@Inject
lateinit var viewModelFactory: ViewModelProvider.Factory
val viewModel: ItemViewModel by viewModels {
    viewModelFactory
}
override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    viewModel.loadItem(args.itemId)
    val bindings = ItemFragmentBinding.inflate(inflater, container, false).apply {
        viewmodel = viewModel
        buttonSave.setOnClickListener{viewModel. viewModelScope.launch {
        viewModel.saveItem()
        findNavController().navigateUp()
    }}

    }

    bindings.lifecycleOwner = this
    return bindings.root
}

ItemViewModel：

var item: LiveData<Item>? = null

fun loadItem(id: String) {
    viewModelScope.launch {
        item = repository.getItemFlow(id).asLiveData()
    }
}

suspend fun saveItem() {
    item!!.value!!.someField = "hi"
    repository.updateItem(item!!.value!!)
}

Answer 1

问题出在项目适配器中。适配器需要DiffUtil.ItemCallback的正确实现

在这种情况下：

private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<Contador>() {
// The ID property identifies when items are the same.
override fun areItemsTheSame(oldItem: Contador, newItem: Contador) =
    oldItem.id == newItem.id

// Check the properties that can change, or implements the equals method in Item class
override fun areContentsTheSame(
    oldItem: Item, newItem: Item) = oldItem.someField == newItem.someField

}