使用 viewModel 作为 jetpack compose 中的单一事实来源

Question

let's say we have a viewModel that has a value called apiKey inside. Contents of this value is received from DataStore in form of a Flow and then, it is exposed as LiveData. On the other hand we have a Fragment called SettingsFragment, and we are trying to display that apiKey inside a TextField, let the user modify it and save it in DataStore right away. The solution that I'm currently using is down below, but the issue is that the UI gets very laggy and slow when changes are being made to the text. My question is that what is the best way to implement this and still have a single source of truth for our apiKey?

class SettingsViewModel() : ViewModel() {

    val apiKey = readOutFromDataStore.asLiveData()

    fun saveApiKey(apiKey: String) {
        viewModelScope.launch(Dispatchers.IO) {
            saveToDataStore("KEY", apiKey)
        }
    }
}

/** SettingsFragment **/
...

@Composable
fun ContentView() {
    var text = mViewModel.apiKey.observeAsState().value?.apiKey ?: ""

    Column() {
        OutlinedTextField(
            label = { Text(text = "API Key") },
            value = text,
            onValueChange = {
                text = it
                mViewModel.saveApiKey(it)
            })
    }
}

Answer 1

have you tried removing text = it from your textfield onValueChange ? If you're observing the value form the viewModel it should change automatically

Answer 2

Don't save the TextField's value in the onValueChange event to the data store on every key press - which is almost certainly slowing you down - especially if you are using the same thread. Use a local state variable and only update the data store when the user either moves the focus elsewhere or they save what's on the screen through some button press. You also need to avoid mixing UI threading with data storage threading which should be on the IO thread. Here is one possible solution:

@Composable
fun ContentView() {
    var text by remember { mutableStateOf(mViewModel.apiKey ?: "")}

    Column() {
        OutlinedTextField(
            label = { Text(text = "API Key") },
            value = text,
            onValueChange = {
                text = it
            },
            modifier = Modifier.onFocusChanged { // Save text})
    }

    // Or add a button and save the text when clicked.
}