Why can I reference Application in ViewModel when I use Hilt in Android Studio?

I use Hilt as DI in Android Studio project. I know "A ViewModel must never reference a view, Lifecycle, or any class that may hold a reference to the activity context."

So you can find that there is a warning information in Image A for Code A.

But the ViewModelComponent of Hilt has bound Application, you can see the article.

1: I don't know why private val appContext: Application in ViewModel doesn't display warning information, does it mean I can use Application in ViewModel when I use Hilt? could you tell me?

2: BTW, private val appContext: Application displays the information below, why?

Constructor parameter is never used as a property

Code A

@HiltViewModel
class RecordSoundViewModel @Inject constructor(
    @ApplicationContext private val myContext: Context,    //Android Studio displays warning information
    private val appContext: Application,                   // Why doesn't it dsiplay warning information
    private val savedStateHandle: SavedStateHandle
): ViewModel()
{
     ...
}

Image A

It might just be the lint seeing Context inside a ViewModel() and complaining about it. Because you might be giving a Context that lives shorter than the ViewModel.

class MyViewModel: ViewModel() {
    //will complain about leaking context
    val ctx: Context = Context()
}

Injecting something that uses ApplicationContext into a ViewModel is a valid use case.

@Module
@InstallIn(SingletonComponent::class)
object WorkManagerModule {

    @Provides
    @Singleton
    fun provideWorkManager(@ApplicationContext context: Context): WorkManager {
        return WorkManager.getInstance(context)
    }
}

@HiltViewModel
class MyViewModel @Inject constructor(
    val workManager: WorkManager
)

For 2: Lint is telling you to remove private val. Since you are not using it as a property, val/var is not needed.

@HiltViewModel
class MyViewModel @Inject constructor(
    savedStateHandle: SavedStateHandle
) {
    //not complaints about property
    val myId = savedStateHandle.get<String>("MyId")
}

If you want to use it as a property you must add val/var.

@HiltViewModel
class MyViewModel @Inject constructor(
    savedStateHandle: SavedStateHandle
) {
    fun getMyIdFromSaveState(): String? {
        //will complain that it does not know savedStateHandle, you must add val or var.
        return savedStateHandle.get<String>("MyId")
    }
}

Try AndroidViewModel as follow:

@HiltViewModel
class RecordSoundViewModel @Inject constructor(
    private val appContext: Application,                
): AndroidViewModel(appContext) {
    ....
}

No need to pass application reference in when initializing viewModel in Fragment/Activity

private val viewModel : RecordSoundViewModel by viewModels()