Can anyone check if I'm doing something wrong with instantiating a viewmodel? here is the code:

@Preview
@Composable
fun LoginScreenPreview(){
    val navController = rememberNavController()
    val main: MainActivity = MainActivity()
    val myfactory = MainViewModelFactory(Database.getInstance(main.applicationContext).Dao, main.application)
    val viewModel: MainViewModel = viewModel(
        factory =myfactory
    )
    //TextField(value ="xxx", onValueChange ={} )
    LoginScreen(navController,  viewmodel = viewModel)
}

and viewmodel factory:

class MainViewModelFactory(
    private val dataSource: Dao,
    private val application: Application
): ViewModelProvider.Factory{
    @Suppress("unchecked_cast")
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(MainViewModel::class.java)) {
            return MainViewModel(dataSource, application) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

The login screen only has basic fields such as textfields and a button, but uses data from viewmodel. Can't preview anything as of this state.

You can't instantiate an Activity by calling its constructor, you should not pass a navigation controller to your composables (pass a lambda), and you should be providing fakes for the dependencies (viewmodel)

Thank you for answering. Why should I not pass the navController, isn't it more convenient this way? I'll learn about the last part, creating fakes for the dependencies.

It makes your previews and tests that much harder, it's best practice to pass a lambda, check this https://developer.android.com/jetpack/compose/navigation#testing

So all of a sudden clean architecture makes sense, I've been struggling (failing) to get my viewmodels with repo or dao arguments to work in preview. Probably unrelated.

I have a sample project here that you may find useful for reference https://github.com/fvilarino/Weather-Sample/tree/feature/compose