I am attempting to add Hilt DI to a view model class.
It's not clear to be from the docs (in layman's terms) what the constructor is used for?
All the Google docs also indicate you need to add this : ViewModel interface after the constructor but I am also curious what purpose that interface serves?
#HiltViewModel
class MyViewModel #Inject constructor(
) : ViewModel() {
private val _myVal: MutableState<String> = mutableStateOf("")
val myVal get() = _myVal.value
fun setMyVal (myVal: String) {
_myVal.value = phoneNumber
}
}
Related
i have a problem.
I try pass a variable <ArrayList<List>> betwenne two ViewModels.
ViewModel A:
#HiltViewModel
class RouteTrackViewModel #Inject constructor(
application: Application
) : ViewModel(){
private val locationLiveData = LocationLiveData(application)
private var finalRoute = ArrayList<List<Double>>()
private var finalTime : Duration = Duration.ZERO
fun getLocationLiveData() = locationLiveData
fun getFinalRoute() = finalRoute
...
}
ViewModel B:
#HiltViewModel
class RouteSaveViewModel #Inject constructor(
private var routeTrackViewModel : RouteTrackViewModel
) : ViewModel() {
fun getLocationLiveData() = routeTrackViewModel.getLocationLiveData()
fun getRouteLocation() = routeTrackViewModel.getFinalRoute()
}
if i use like that give me this error:
Injection of an #HiltViewModel class is prohibited since it does not create a ViewModel instance correctly.
Access the ViewModel via the Android APIs (e.g. ViewModelProvider) instead.
Injected ViewModel: com.xxxxxxxxxxxxxx.xxxxxxxxxxxx.presentation.routes.route_track.RouteTrackViewModel
please can you help me to fine a good solution?
I expect to have access to final Route in Route Save ViewModel.
I need these values to show on Mapbox a polyline and create a form to save the route later in a JSON file and send it to my database.
In my activity, I have multiple variables being initiated from Intent Extras. As of now I am using ViewModelFactory to pass these variables as arguments to my viewModel.
How do I eliminate the need for ViewModelFacotory with hilt
Here are two variables in my Activity class
class CommentsActivity : AppCompatActivity() {
private lateinit var viewModel: CommentsViewModel
override fun onCreate(savedInstanceState: Bundle?) {
val contentId = intent.getStringExtra(CONTENT_ID_FIELD) //nullable strings
val highlightedCommentId = intent.getStringExtra(HIGHLIGHTED_COMMENT_ID_RF) //nullable strings
val commentsViewModelFactory = CommentsViewModelFactory(
contentId,
highlightedCommentId
)
viewModel = ViewModelProvider(this, commentsViewModelFactory[CommentsViewModel::class.java]
}
}
Here is my viewModel
class CommentsViewMode(
contentId : String?,
highlightedCo;mmentId : String?,
) : ViewModel() {
//logic code here
}
My app is already set up to use hilt but in this case How can I pass these 2 variables and eliminate the viewModelFactory entirely
The trick is to initialize those variables only once, while the activity can be created multiple times. In my apps, I use a flag.
View model:
class CommentsViewModel : ViewModel() {
private var initialized = false
private var contentId : String? = null
private var highlightedCommentId : String? = null
fun initialize(contentId : String?, highlightedCommentId : String?) {
if (!initialized) {
initialized = true
this.contentId = contentId
this.highlightedCommentId = highlightedCommentId
}
}
//logic code here
}
Also, you should know that there is an open issue in dagger project exactly for this capability:
https://github.com/google/dagger/issues/2287
You're welcome to follow the progress.
If you want to use hilt effectively u can follow this steps
Use #HiltViewModel in your view model
#HiltViewModel
class MyViewModel #inject constructor(private val yrParameter): ViewModel {}
Also you no longer need any ViewModelFactory! All is done for you! In your activity or fragment, you can now just use KTX viewModels() directly.
private val viewModel: MyViewModel by viewModels()
Or if you want to use base classes for fragment and activity you can use this code to pass viewModel class
abstract class BaseFragment<V: ViewModel, T: ViewDataBinding>(#LayoutRes val layout: Int, viewModelClass: Class<V>) : Fragment() {
private val mViewModel by lazy {
ViewModelProvider(this).get(viewModelClass)
}
}
I'm using Dagger-Hilt for dependency injection in my Android project, now I have this situation where I have a base abstract Fragment
BaseViewModel.kt
abstract class BaseViewModel constructor(
val api: FakeApi,
) : ViewModel() {
//...
}
Here, I have a dependency which is FakeApi. What I'm trying to do is to inject the FakeApi into the BaseViewModel to be available in the BaseViewModel and all its children.
The first approach I tried is using the constructor injection and inject it to the child and pass it to the super using the constructor.
TaskViewModel.kt
#HiltViewModel
class TaskViewModel #Inject constructor(
api: FakeApi
) : BaseViewModel(api){
}
This approach works fine, but I don't need to pass the dependency from the child to the super class, I need the FakeApi to be automatically injected in the BaseViewModel without having to pass it as I have three levels of abstraction (There is another class inheriting from the TaskViewModel) So I have to pass it two times.
The second approach was to use the field injection as follows
BaseViewModel.kt
abstract class BaseViewModel: ViewModel() {
#Inject
lateinit var api: FakeApi
//...
}
TaskViewModel.kt
#HiltViewModel
class TaskViewModel #Inject constructor(): BaseViewModel() {
}
This approach didn't work for me and the FakeApi wasn't injected and I've got an Exception
kotlin.UninitializedPropertyAccessException: lateinit property api has not been initialized
My questions are
Why field injection doesn't work for me?
Is there any way to use constructor injection for the super class instead of passing the dependency from the child?
Thanks to this Github Issue I figured out that the problem is that you can't use the field injected properties during the ViewModel constructor initialization, but you still use it after the constructor -including all the properties direct initialization- has been initialized.
Dagger firstly completes the constructor injection process then the field injection process takes place. that's why you can't use the field injection before the constructor injection is completed.
❌ Wrong use
abstract class BaseViewModel : ViewModel() {
#Inject
protected lateinit var fakeApi: FakeApi
val temp = fakeApi.doSomething() // Don't use it in direct property declaration
init {
fakeApi.doSomething() // Don't use it in the init block
}
}
✔️ Right use
abstract class BaseViewModel : ViewModel() {
#Inject
protected lateinit var fakeApi: FakeApi
val temp: Any
get() = fakeApi.doSomething() // Use property getter
fun doSomething(){
fakeApi.doSomething() // Use it after constructor initialization
}
}
Or you can use the by lazy to declare your properties.
I tested and I see that field injection in base class still work with Hilt 2.35. I can not get the error like you so maybe you can try to change the Hilt version or check how you provide FakeApi
abstract class BaseViewModel : ViewModel() {
#Inject
protected lateinit var fakeApi: FakeApi
}
FakeApi
// Inject constructor also working
class FakeApi {
fun doSomeThing() {
Log.i("TAG", "do something")
}
}
MainViewModel
#HiltViewModel
class MainViewModel #Inject constructor() : BaseViewModel() {
// from activity, when I call this function, the logcat print normally
fun doSomeThing() {
fakeApi.doSomeThing()
}
}
AppModule
#Module
#InstallIn(SingletonComponent::class)
class AppModule {
#Provides
fun provideAPI(
): FakeApi {
return FakeApi()
}
}
https://github.com/PhanVanLinh/AndroidHiltInjectInBaseClass
After many searches on the Internet, I think the best solution is to not use initializer blocks init { ... } on the ViewModel, and instead create a function fun initialize() { ... } that will be called on the Fragment.
BaseViewModel.kt
#HiltViewModel
open class BaseViewModel #Inject constructor() : ViewModel() {
#Inject
protected lateinit var localUserRepository: LocalUserRepository
}
OnboardingViewModel.kt
#HiltViewModel
class OnboardingViewModel #Inject constructor() : BaseViewModel() {
// Warning: don't use "init {}", the app will crash because of BaseViewModel
// injected properties not initialized
fun initialize() {
if (localUserRepository.isLoggedIn()) {
navigateToHomeScreen()
}
}
}
OnBoardingFragment.kt
#AndroidEntryPoint
class OnBoardingFragment() {
override val viewModel: OnboardingViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.initialize()
}
}
Sources:
https://github.com/google/dagger/issues/2507
the answers on this question
My ViewModel:
class LoginViewModel #ViewModelInject constructor(
private val loginUseCase: LoginUseCase
) : ViewModel() {
val currentResult: MutableLiveData<String> by lazy {
MutableLiveData<String>()
}
fun loginUseCase(username: String, password: String) {
viewModelScope.launch {
loginUseCase.invoke(username, password).apiKey.let {
currentResult.value = it
}
}
}
}
Is being used by my MainActivity:
#AndroidEntryPoint
class MainActivity : AppCompatActivity() {
private val loginViewModel: LoginViewModel by viewModels()
And I know that the ViewModelProvider is expecting a empty constructor but I need to use the LoginUseCase:
class LoginUseCase #Inject constructor(
private val apiService: ApiServiceImpl
) : UseCase<Unit>() {
suspend operator fun invoke(username: String, password: String) =
apiService.login(username, password)
}
Inside the modelView, but i get the error:
Cannot create an instance of class com.example.myboards.ui.login.LoginViewModel
in runtime, and I dont know how I could manage the LoginUseCase inside the LoginViewModel
Provide a ViewModel by annotating it with #HiltViewModel and using the #Inject annotation in the ViewModel object's constructor.
#HiltViewModel
class LoginViewModel #Inject constructor(
private val loginUseCase: LoginUseCase
) : ViewModel() {
...
}
Hilt needs to know how to provide instances of ApiServiceImpl, too. Read here to know how to inject interface instances with #Binds.
Let me know If you still have a problem.
I have this class:
class MyViewModel #Inject constructor(repository: MyRepository): ViewModel () {
lateinit var myLiveData: LiveData<User>
fun signIn(credential: AuthCredential) {
myLiveData = repository.signIn(credential)
}
val otherLiveData = repository.signOut() //Works fine
}
The problem is that the repository cannot be used inside the signIn function and I don't know why. However, the second call to signOut works. Can anyone please help?
Creating a class with primary constructor and parameter like this:
class MyViewModel #Inject constructor(repository: MyRepository): ViewModel () { ... }
leads to the fact that repository parameter is not a property, which means it can't be used in other functions of the class. But it can be used in the initializer blocks and in property initializers declared in the class body:
class MyViewModel(repo: MyRepository) {
val repository = repo
}
However, Kotlin has more concise syntax for declaring properties and initializing them from the primary constructor, using val or var keyword:
class MyViewModel #Inject constructor(val repository: MyRepository): ViewModel () { ... }
If you declare parameter with val or var keyword it will be treated as a property and be available in other functions of the class.
More info about constructors and parameters in Kotlin.