Hilt

MyApplication.kt

@HiltAndroidApp
class MyApplication : Application() {
    
    @Inject
    @UserModelSingletonQualifier
    lateinit var singletonUserModel: UserModel

    override fun onCreate() {
        super.onCreate()  
        
        singletonUserModel.value += "MyApplication"
    }
}

SplashActivity.kt

@AndroidEntryPoint
class SplashActivity : AppCompatActivity() {

    private val splashViewModel by viewModels<SplashViewModel>()

    private lateinit var binding: SplashActivityBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = SplashActivityBinding.inflate(LayoutInflater.from(this))
        setContentView(binding.root)
        
        Timber.e("singleton userModel = ${splashViewModel.singletonUserModel}")
        
        splashViewModel.get("demo_key")
            .observe(this, Observer { 
                Timber.e("demo_key = $it")
            })

        splashViewModel.put("demo_key", "demo_value")
        
        binding.buttonFeature.setOnClickListener {
            val clazz = Class.forName("com.kienht.dagger.hilt.feature.FeatureActivity")
            startActivity(Intent(this, clazz))
        }
    }
}

SplashViewModel.kt

class SplashViewModel @ViewModelInject constructor(
    @UserModelSingletonQualifier val singletonUserModel: UserModel,
    @Assisted private val savedStateHandle: SavedStateHandle
) : ViewModel() {

    fun get(key: String) = savedStateHandle.getLiveData<String>(key)

    fun put(key: String, value: String) = savedStateHandle.set(key, value)

}