Expected methods do not exists MutableStateFlow<List<T>>() for manipulation-CodePudding

I have this MutableStateFlow<>() declaration:

private val _books = MutableStateFlow<List<Book>>(emptyList())

I am trying to append/add results from the database:

fun fetchAllBooks(user_id: Long) = viewModelScope.launch(Dispatchers.IO) {
    dbRepository.getAllUsersBooks(user_id).collect{ books ->
        _books.add() // Does not exist, nor does the 'postValue' method exists
    }
}

But, this does not work as I though, non of the expected methods exists.

CodePudding user response：

If you need to update the state of a MutableStateFlow, you can set the value property:

fun fetchAllBooks(user_id: Long) = viewModelScope.launch(Dispatchers.IO) {
    dbRepository.getAllUsersBooks(user_id).collect{ books ->
        _books.value = books
    }
}

It will trigger events on collectors if the new value is different from the previous one.

But if getAllUsersBooks already returns a Flow<List<Book>>, you could also simply use it directly instead of updating a state flow.

If you really want a StateFlow, you can also use stateIn:

fun fetchAllBooks(user_id: Long) = dbRepository.getAllUsersBooks(user_id)
    .flowOn(Dispatchers.IO) // likely unnecessary if your DB has its own dispatcher anyway
    .stateIn(viewModelScope)

CodePudding user response：

You are actually declaring the immutable list and trying to add and remove data instade of that use mutable list to add or remove data from list like here :-

private var _bookState = MutableStateFlow<MutableList<Book>>(mutableListOf())
private var books=_bookState.asStateFlow()
var bookList= books.value

and to send the data to the state use this:-

viewModelScope.launch {
        _bookState.value.add(BookItem)     


 }
viewModelScope.launch {
            _bookState.value.remove(BookItem)    
}

I hope this will work out for you if you have any query pls tell me in comment.