LazyColumn item not updated accordingly while list in room table already updated - android-room

Question

When the Icon clicked, viewModel.onLockIconClicked(it) is called to reverse the value of isLock in db.
The Icon is expected to be updated according based on the value of isLock.
I've checked the value did reversed in db table. But LazyColumn not update accordingly.
What did I miss? Thanks a lot!
Ex, initially, Screen: icon = lock and Db: isLock = true,
when Icon clicked, Screen: icon = lock and Db: isLock = false,
while expected is Screen: icon = lock_open and Db: isLock = false.
ListScreen:
#Composable
fun ListScreen(context: Context) {
val viewModel: ListViewModel =
viewModel(factory = ListViewModelFactory(Db.getInstance(context)))
val list by viewModel.list.collectAsState(initial = emptyList())
Scaffold() {
SwipeRefresh(
state = rememberSwipeRefreshState(viewModel.isRefreshing),
onRefresh = { }
) {
LazyColumn(
state = rememberLazyListState(),
) {
items(list) {
Row() {
Icon(
painter = painterResource(if (it.isLock) R.drawable.ic_baseline_lock_24 else R.drawable.ic_baseline_lock_open_24),
contentDescription = null,
modifier = Modifier.clickable() { viewModel.onLockIconClicked(it) }
)
Text(it.code)
}
}
}
}
}
}
ListViewModel:
class ListViewModel(db: Db) : ViewModel() {
private val sumDao = db.sumDao()
val list = sumDao.getAllRows()
var isRefreshing by mutableStateOf(false)
private set
//init
init {
viewModelScope.launch(Dispatchers.IO) {
val initialCodeList = listOf("aaa", "bbb")
for (code in initialCodeList) {
val sum = Sum()
sum.code = code
sumDao.insert(sum)
}
}
}
fun onLockIconClicked(sum: Sum) {
sum.isLock = !sum.isLock
viewModelScope.launch(Dispatchers.IO) {
sumDao.update(sum)
}
}
}
class ListViewModelFactory(private val db: Db) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(ListViewModel::class.java)) {
#Suppress("UNCHECKED_CAST")
return ListViewModel(db) as T
}
throw IllegalArgumentException("Unknown ViewModel class")
}
}
Sum:
#Entity(tableName = "sum", primaryKeys = ["code"])
data class Sum(
#ColumnInfo(name = "code")
var code: String = "",
#ColumnInfo(name = "is_lock")
var isLock: Boolean = true
)
SumDao:
#Dao
interface SumDao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insert(sum: Sum): Long
#Update(onConflict = OnConflictStrategy.REPLACE)
suspend fun update(sum: Sum): Int
#Delete
suspend fun delete(sum: Sum): Int
#Query("select * from sum")
fun getAllRows(): Flow<List<Sum>>
}
Db:
#Database(entities = [Sum::class], version = 1, exportSchema = false)
abstract class Db : RoomDatabase() {
abstract fun sumDao(): SumDao
companion object {
#Volatile
private var INSTANCE: Db? = null
fun getInstance(context: Context): Db {
return INSTANCE ?: synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
Db::class.java,
"db"
)
.fallbackToDestructiveMigration()
.build()
INSTANCE = instance
return instance
}
}
}
}

Answer 1

Consider taking the State-in-Compose for a better understanding of the concepts of state-handling in Compose.
I'm sorry but the information that you have provided is massive, so I can't pinpoint the source of the bug, but here's what you can do for now:
In your Dao class, just replace the words Flow<List<Sum>> with LiveData<List<Sum>>
In your ViewModel, you can get access to the LiveData inside the init like so
var list by mutableStateListOf<Sum>()
init{
sumDao.getAllRows().observeForever{
list = it
}
}
Now, list would ideally be updated every time the value in the databse changes, which infact would trigger recompositions since I am using a direct mutableStateListOf object here.
The problem may lie anywhere:
Since the class Sum is a custom-made class, it may have been experiencing issues triggering recompositions, which is a common problem among new developers, and even some experienced ones nowadays.
Since you are declaring the viewModel inside the Composable, wrong instances of ViewModels may have been passed around, leading to state-inconsistency - always try to declare your viewModels in the top-most layer possibly, i.e., somewhere like the onCreate method of the activity. Fragments are discourages so you should not face any problems over there.
Since you were not actively observing the Flow anywhere, that could have lead to the variable not being updated at all in the ViewModel, which would again lead to UI-inconsistency.