I have a few items stored in Room, and I want to add a new one. Here is what I have tried:

interface ItemDao {
    @Query("SELECT * FROM item_table")
    fun getItems(): List<Intem>

    @Insert(onConflict = IGNORE)
    fun addItem(item: Item)
}

My repo is very simple:

interface ItemRepository {
    fun getItemsFromRoom(): List<Item>

    fun addItemToRoom(item: Item)
}

And inside the View Model class I do:

class ItemsViewModel @Inject constructor(
    private val repo: ItemRepository
) : ViewModel() {
    var items by mutableStateOf(emptyList<Item>())

    fun getItems() = viewModelScope.launch {
        items = repo.getItemsFromRoom()
    }

    fun addItem(item: Item) = viewModelScope.launch(Dispatchers.IO) {
        repo.addItemToRoom(ietm)
    }
}

And inside the composable I do:

LazyColumn(
    modifier = Modifier.fillMaxSize()
) {
    items(
       items = viewModel.items
    ) { item ->
        Text(item.name)
    }
}

When I open the app, I get all the data from Room correctly. When I want to add another item, I press a button, a dialog is displayed, I write the data and I hit add. The problem comes when the dialog is closed, I cannot see the new data, unless I close and reopen the app. Why isn't the state changed when I add a new item in Room? How to solve this?

CodePudding user response：

Your query returns List of items. To refresh UI list you need to call getItemsFromRoom function again. It's not updated automatically because it's only simple List. I would suggest to return Flow<List<Item>> instead of List<Item> and collect from that flow to update items automatically then database changes

Where's official android codelab, where you can follow step by step to implement this.

CodePudding user response：

You should emit a reactive data stream (like LiveData or Flow) from your Dao if you want to get data updates. It's better to use a Flow here.

interface ItemDao {
    @Query("SELECT * FROM item_table")
    fun getItems(): Flow<List<Intem>>

    @Insert(onConflict = IGNORE)
    fun addItem(item: Item)
}

interface ItemRepository {
    fun getItemsFromRoom(): Flow<List<Item>>

    fun addItemToRoom(item: Item)
}

And in your ViewModel, you don't need a new getItems function to be called from the UI. Instead you can directly do this:

class ItemsViewModel @Inject constructor(
    private val repo: ItemRepository
) : ViewModel() {

    val items = repo.getItemsFromRoom()

    fun addItem(item: Item) = viewModelScope.launch(Dispatchers.IO) {
        repo.addItemToRoom(ietm)
    }
}

Finally, in the UI, you can collect this Flow like this:

val items by viewModel.items.collectAsState(initialValue = emptyList())
LazyColumn(
    modifier = Modifier.fillMaxSize()
) {
    items(items = items) { item ->
        Text(item.name)
    }
}