I'm using Koin 2.1.6 in my app module. Here are the artefacts I use
implementation "org.koin:koin-android:2.1.6"
implementation "org.koin:koin-core:2.1.6"
implementation "org.koin:koin-androidx-viewmodel:2.1.6"
implementation "org.koin:koin-androidx-fragment:2.1.6"
And Koin module is
val userModule = module {
viewModel { (handle: SavedStateHandle) -> UserViewModel(get(), handle) }
}
class UserViewModel(
val iService: IService, //injected from core module
val handle: SavedStateHandle
) : ViewModel()
I use this ViewModel on UserFragment
private val viewModel: UserViewModel by stateViewModel()
UserFragment contains an internal fragment- UserUpdates, inflated from layout, shares the above ViewModel.
<fragment android:name="UserUpdates"
android:id="#id/fragment_user_updates"
android:width="match_parent"
android:height="wrap_content" />
On UserUpdates fragment, I set the ViewModel as follows
private val viewModel: UserViewModel by stateSharedViewModel()
However, I found out that ViewModel instances generated are not shared. In fact they are created as new objects. Is there anything I miss out here?
I believe you need to use stateSharedViewModel (instead of stateViewModel you have right now)
I have just learnt manual dependency injection, but I am trying out Hilt to handle these dependency injections.
I want to inject a ViewModel into a Fragment. The fragment is contained within an Activity. Right now, I have added the annotations to Application, Activity, and Fragment.
#HiltAndroidApp
class MovieCatalogueApplication : Application()
#AndroidEntryPoint
class MainActivity : AppCompatActivity() {
...
}
#AndroidEntryPoint
class HomeFragment : Fragment() {
private lateinit var binding: FragHomeBinding
private val viewmodel: HomeViewModel by viewModels()
...
As can be seen, my HomeFragment depends on HomeViewModel. I have added a ViewModel injection as described here like so.
class HomeViewModel #ViewModelInject constructor(
private val movieRepository: MovieRepository,
private val showRepository: ShowRepository,
#Assisted private val savedStateHandle: SavedStateHandle
) : ViewModel() {
...
}
However, the ViewModel requires two repositories. Right now, my MovieRepository is like so.
class MovieRepository (private val movieApi: MovieService) {
...
}
In the above code, MovieService will be created by Retrofit using the Retrofit.create(class) method. The interface used to create MovieService is like so.
interface MovieService {
...
}
To get my Retrofit instance, I am using the following code.
object RetrofitService {
...
private var _retrofit: Retrofit? = null
val retrofit: Retrofit
get() {
return when (_retrofit) {
null -> {
_retrofit = Retrofit.Builder()
.client(client)
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build()
_retrofit!!
}
else -> _retrofit!!
}
}
}
I am not too sure how I can inject the Retrofit into the Repository to be used by my ViewModel later on. Could someone give me some pointers or step-by-step instructions on how to do this?
Apparently, it is not as hard as it seems.
You have to first define the binding information to Hilt. Binding information tells Hilt how to provide the instances of the dependency specified. Because MovieService is created using a Retrofit (which is a 3rd-party class not created by yourself) using the builder pattern, you can't use the constructor injection and you have to instead use Hilt modules and the annotation #Provides to tell Hilt about this binding information.
As described in the doc, the annotated function in the Hilt module you have created will supply the following information to Hilt so that Hilt can provide the instances of the dependency.
• The function return type tells Hilt what type the function provides instances of.
• The function parameters tell Hilt the dependencies of the corresponding type.
• The function body tells Hilt how to provide an instance of the corresponding type. Hilt executes the function body every time it needs to provide an instance of that type.
In the end, you only need to modify the MovieRepository class, add a module for each repository, and annotate the function that tells Hilt how to provide the service instance created with Retrofit with #Provides.
Code.
class MovieRepository #Inject constructor(
private val movieApi: MovieService
) {
...
}
interface MovieService {
...
}
#Module
#InstallIn(ActivityRetainedComponent::class)
object MovieModule {
#Provides
fun provideMovieService(): MovieService
= RetrofitService.retrofit.create(MovieService::class.java)
}
As you can see, the ActivityRetainedComponent is referred in the #InstallIn annotation because the Repository is to be injected to a ViewModel. Each Android component is associated to different Hilt components.
I want to initialize ViewModel in Activity using androidx library
I have tried what documentation says but it is not working. the ".of" is not resolved.
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.ViewModelProvider
import com.example.myapplication.databinding.ActivityMainBinding`
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val binding: ActivityMainBinding = DataBindingUtil.setContentView(
this, R.layout.activity_main)
binding.setLifecycleOwner(this)
var model = ViewModelProvider.of(this).get(SheduleViewModel::class.java)
}
}
of is not resolved, maybe there are another way to do it in androidx
Updated answer:
Things changed a little bit, as the previously needed dependency - ViewModelProviders - got deprecated (see the old answer for details). You can now use the ViewModelProvider constructor directly.
So, in this case, the answer would be:
private val viewModel = ViewModelProvider(this).get(SheduleViewModel::class.java)
Note that, however, if you include the androidx.activity:activity-ktx:$Version dependency (a few of the commonly used AndroidX dependencies already include it for you), you can make use of property delegation:
private val viewModel: SheduleViewModel by viewModels()
Which internally will use ViewModelProvider and scope your ViewModel to your Activity. It's just a more concise way of writing the same thing. You can do the same for a Fragment by including the androidx.fragment:fragment-ktx:$Version dependency instead (again, commonly already included by other AndroidX dependencies).
Both the ViewModelProvider constructor and by viewModels() also accept a factory as a parameter (useful for injecting your ViewModel):
private val viewModel =
ViewModelProvider(this, viewModelFactory).get(SheduleViewModel::class.java)
and
private val viewModel: SheduleViewModel by viewModels { viewModelFactory }
Use the one that best suits you.
Old answer:
Add the androidx.lifecycle:lifecycle-extensions:$lifecycleExtensionsVersion dependency in order to import ViewModelProviders.
Updating ViewModel to Lifecycle Version 2.2.0 and Above
The ViewModels (VMs) may theoretically be initialized as class level instance variables using the Kotlin extension library import androidx.fragment.app.viewModels method by viewmodels(). By initializing the VM as a class level instance var it can be accessed within the class.
Question: Is there a downside to initializing the VMs as class level instance variables instead of inside onCreate?
When creating the VMs with the extension function inside onCreate the VMs are only scoped within onCreate and extra code is required to reassign the class level instance variables.
See documentation
ViewModel Overview
Lifecycle
Initialize VM as Class Instance Val
class Fragment : Fragment() {
private val viewModel: SomeViewModel by viewModels()
private fun observeViewState() {
viewModel.feedViewState.observe(viewLifecycleOwner) { viewState ->
//viewState used here.
}
}
}
Initialize VM in onCreate and Reassign Class Instance Var
class Fragment : Fragment() {
private lateinit var viewModel: SomeViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val viewModel: ContentViewModel by viewModels()
this.viewModel = viewModel
}
private fun observeViewState() {
viewModel.feedViewState.observe(viewLifecycleOwner) { viewState ->
//viewState used here.
}
}
}
Passing Arguments/Parameters
// Override ViewModelProvider.NewInstanceFactory to create the ViewModel (VM).
class SomeViewModelFactory(private val someString: String): ViewModelProvider.NewInstanceFactory() {
override fun <T : ViewModel?> create(modelClass: Class<T>): T = SomeViewModel(someString) as T
}
class SomeViewModel(private val someString: String) : ViewModel() {
init {
//TODO: Use 'someString' to init process when VM is created. i.e. Get data request.
}
}
class Fragment: Fragment() {
// Create VM in activity/fragment with VM factory.
val someViewModel: SomeViewModel by viewModels { SomeViewModelFactory("someString") }
}
Enabling SavedState with Arguments/Parameters
class SomeViewModelFactory(
private val owner: SavedStateRegistryOwner,
private val someString: String) : AbstractSavedStateViewModelFactory(owner, null) {
override fun <T : ViewModel?> create(key: String, modelClass: Class<T>, state: SavedStateHandle) =
SomeViewModel(state, someString) as T
}
class SomeViewModel(private val state: SavedStateHandle, private val someString: String) : ViewModel() {
val feedPosition = state.get<Int>(FEED_POSITION_KEY).let { position ->
if (position == null) 0 else position
}
init {
//TODO: Use 'someString' to init process when VM is created. i.e. Get data request.
}
fun saveFeedPosition(position: Int) {
state.set(FEED_POSITION_KEY, position)
}
}
class Fragment: Fragment() {
// Create VM in activity/fragment with VM factory.
val someViewModel: SomeViewModel by viewModels { SomeViewModelFactory(this, "someString") }
private var feedPosition: Int = 0
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
someViewModel.saveFeedPosition((contentRecyclerView.layoutManager as LinearLayoutManager)
.findFirstVisibleItemPosition())
}
override fun onViewStateRestored(savedInstanceState: Bundle?) {
super.onViewStateRestored(savedInstanceState)
feedPosition = someViewModel.feedPosition
}
}
For me, the only thing that worked:
implementation 'androidx.fragment:fragment:1.2.4'
PS. This is for someone who is using java and got stuck for a while like I did and this SO answer comes up in google all the time.
Apparently, the API has change as of this date (6 May 2020), I had to do this to get it working.
// 1. Create a ViewModel Class Let's call it AppStateViewModel
// 2. Put below code Inside Activity onCreate like this:
ViewModelProvider.Factory factory = new ViewModelProvider.NewInstanceFactory();
appStateManager = new ViewModelProvider(this, factory).get(AppStateViewModel.class);
ViewModelProviders: This class is deprecated. Use the constructors for ViewModelProvider directly.
Examples in Kotlin
This is how you can use ViewModelProvider directly:
If your view-model is extending AndroidViewModel with just one argument, the app - then you can use the default AndroidViewModelFactory and you don't have to write a new Factory. Example:
// Activity / fragment class
private lateinit var viewModel: MyOwnAndroidViewModel
// onCreate
viewModel = ViewModelProvider(
this,
ViewModelProvider.AndroidViewModelFactory(application)
).get(MyOwnAndroidViewModel::class.java)
If your view-model is only extending the ViewModel without extra arguments then use the NewInstanceFactory().
// Activity / fragment class
private lateinit var viewModel: MyOwnViewModel
// onCreate
viewModel = ViewModelProvider(
this,
ViewModelProvider.NewInstanceFactory()
).get(MyOwnViewModel::class.java)
Adam's answer above covers other variations as well.
Disclaimer: Still learning basic Android development - if there's any problem with the code, let me know in comments.
(How to) Use ViewModel from Android Architecture Component :
Add the Google Maven repository (Optional, just verify that)
Android Studio projects aren't configured to access this repository by default.
To add it to your project, open the build.gradle file for your project (not the ones for your app or module) and add the google() repository as shown below:
allprojects {
repositories {
google()
jcenter()
}
}
Declaring dependencies
Open your app-level build.gradle file,
Go to dependencies{} block
Put implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version" for AndroidX version, $lifecycle_version here is latest version defined.
For Pre-AndroidX use implementation "android.arch.lifecycle:viewmodel:1.1.1" (1.1.1 is the last version from this artifact i guess.)
In your activity, use like this syntax
Import this class :
import androidx.lifecycle.ViewModelProviders; for AndroidX
import android.arch.lifecycle.ViewModelProviders; when using Pre-AndroidX
And obtain your ViewModel like following
ViewModelProviders.of(this).get(ProfileObservableViewModel::class.java) // Kotlin syntax
---- or ----
ViewModelProviders.of(this).get(ProfileObservableViewModel.class); // Java syntax
In your app gradle file make sure you have added below dependencies:
For Activity use:
implementation "androidx.activity:activity-ktx:1.4.1"
For Fragment use:
implementation 'androidx.fragment:fragment:1.4.1'
Paste the code below in build.gradle(:app)
implementation 'androidx.fragment:fragment-ktx:1.4.1'
paste the following or similar(relevant to your settings) in app.gradle under dependencies
implementation 'androidx.navigation:navigation-fragment-ktx:2.3.5'
implementation 'androidx.navigation:navigation-ui-ktx:2.3.5'
I add the last version of this dependency from
https://developer.android.com/kotlin/ktx/extensions-list
implementation "androidx.activity:activity-ktx:1.4.0"
I have the following LoginFragment that uses Dagger to inject its fields:
class LoginFragment : DaggerFragment() {
#Inject
lateinit var viewModelFactory: ViewModelProvider.Factory
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel = ViewModelProviders.of(this, viewModelFactory)
.get(LoginViewModel::class.java)
}
I also have a corresponding test that mocks the LoginViewModel according to the documentation from Google: "You can create the fragment and provide it a mock ViewModel."
#MediumTest
#RunWith(AndroidJUnit4::class)
class LoginFragmentTest {
#Mock
private lateinit var viewModel: LoginViewModel
#Before
fun setUp() {
loginFragment = LoginFragment()
loginFragment.viewModelFactory = createMockViewModelFactory(viewModel)
activityRule.activity.setFragment(loginFragment)
}
}
The problem is that when the onAttached method of the fragment is invoked, Dagger overrides the viewModelFactory with its own object, thus replacing my mock.
How can I prevent Dagger from overriding my mock object?
In the android-architecture-components samples on Github Google have an interesting solution.
They inject the activities trough ActivityLifecycleCallbacks. For instrumented tests they use a TestApp that does not register ActivityLifecycleCallbacks so it injects nothing.
Just like in your example the ViewModel.Factory is package private so in the test you can assign it yourself.
For Fragments there is FragmentManager.FragmentLifecycleCallbacks class which can be used. Instead of the Fragment injecting itself in onActivityCreated your production activity injects the Fragment using FragmentLifecycleCallbacks. You can create a testing activity which does not inject the fragment and you can create a mock factory yourself.
I am trying to write a sample app using Android architecture components and but even after trying for days I could not get it to work. It gives me the above exception.
Lifecycle owner:-
public class MainActivity extends LifecycleActivity {
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView textView = findViewById(R.id.tv_user);
PostViewModel viewModel = ViewModelProviders.of(this).get(PostViewModel.class);
viewModel.loadPosts();
viewModel.getPost().observe(this, new Observer<Post>() {
#Override
public void onChanged(#Nullable Post post) {
if(post != null) {
textView.setText(post.toString());
}
}
});
}
}
ViewModel:-
public class PostViewModel extends ViewModel {
private MediatorLiveData<Post> post;
private PostRepository postRepo;
PostViewModel() {
post = new MediatorLiveData<>();
postRepo = new PostRepository();
}
public LiveData<Post> loadPosts() {
post.addSource(postRepo.getPost(),
post -> this.post.setValue(post)
);
return post;
}
#NonNull
public LiveData<Post> getPost() {
return post;
}
}
if you are using Hilt, ensure your activity/fragment is having #AndroidEntryPoint annotation
Make your constructor public.
If you are using Kotlin make sure to replace any annotationProcessor in build.gradle with kapt.
Like:
annotationProcessor "android.arch.persistence.room:compiler:$rootProject.roomVersion"
Will become
kapt "android.arch.persistence.room:compiler:$rootProject.roomVersion"
and add
apply plugin: 'kotlin-kapt' on top of the buidl.gradle file.
Annotation Processing with Kotlin
Make sure your ViewModel has constructor with only one parameter i.e. Application.
example:
public YourViewModel(Application application) {
super(application);
...
DaggerHilt can also be the reason, If you are using it make sure your activity/fragment is having #AndroidEntryPoint annotation on it.
There are few reason to throw the exception . I have mention some of them..
Make sure your view Model class is public
Make sure your view model class constructor is public
Make sure you have added the dependency in your gradle file for
lifecycle also if you use room and other libraries you have added ..
if you create object any other dependent class in your view model
class constructor . Other class can throw error to create the
instance of viewModel
I had this problem following google's roomdb CodeLab. Solution was changing the following.
Edited
Add the following Build dependencies to Gradle file (as of 2/22/2020)
implementation 'androidx.fragment:fragment:1.2.2'
implementation 'androidx.lifecycle:lifecycle-process:2.2.0'
implementation 'androidx.lifecycle:lifecycle-service:2.2.0'
implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:2.2.0'
annotationProcessor 'androidx.lifecycle:lifecycle-compiler:2.2.0'
Imports within the fragment
import androidx.lifecycle.ViewModelProvider;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
Creating the viewModel. Add one of the following methods.
Note: I'v seen this done many ways. I believe the correct way is using getDefaultViewModelProviderFactory(). But I have been using requireActivity().
new ViewModelProvider(requireActivity(),getDefaultViewModelProviderFactory()).get(YourViewModel.class);
|
new ViewModelProvider(requireActivity()).get(YourViewModel.class);
ViewModelProvider Docs
Deprecated
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0-rc01'
annotationProcessor 'androidx.lifecycle:lifecycle-compiler:2.2.0-rc01'
Add #HiltViewModel on top of your viewModel .
For people using Jetpack Compose, Navigation and Hilt
Make sure to use the hiltNavGraphViewModel instead of viewModel.
This is provided by androidx.hilt:hilt-navigation-compose dependency.
More details in the docs.
It was not completely obvious to me, but when getting this error I resolved it by creating a public constructor. My constructor was derived from the Android Developer examples and contained the Repository as a parameter. Creating an additional constructor that was empty with no params and having it public solved the issue.
i.e., in your case
public PostViewModel() {}
Make the class and constructor public it solved my problem .
Extend AndroidViewModel from your ViewModel class.
public class YourViewModel extends AndroidViewModel {
public YourViewModel(Application application) {
super(application);
//Todo: ...
}
}
If you used viewmodel inside your activity check that your activity extends "DaggerAppCompatActivity" or not
For instance
public class UserComments extends AppCompatActivity
change this to
public class UserComments extends DaggerAppCompatActivity
Mostly, Solution is making Class and Constructor Public as the other answers
It may also be a runtime error, check the Logcat Error Logs if there are multiple causes listed.
If you are using Hilt then don't forget to add these four dependencies.
implementation "com.google.dagger:hilt-android:2.28-alpha"
kapt "com.google.dagger:hilt-android-compiler:2.28-alpha"
implementation 'androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha01'
kapt "androidx.hilt:hilt-compiler:1.0.0-alpha01"
Note:- If any of these dependencies are missing you will get Cannot create an instance of class ViewModel error
In my case, the reason was that I was trying to get a shared instance of the ViewModel in my fragment too soon - before the activity was created. What happens when the application is restoring its state after being killed.
Preconditions:
My ViewModel has a public constructor.
My ViewModel has multiple arguments. But this is absolutely fine as I use ViewModelFactory to construct the ViewModel.
My Fragment and Activity shares the same instance of the ViewModel. In other words: Activity creates the ViewModel and the fragment receives the same instance later.
Code in activity:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//factory is constructed using Dagger
val factory = App.get().components().appComponent.getMapViewModelFactory()
//activity creates the instance of MapViewModel
viewModel = ViewModelProviders.of(this, factory)[MapViewModel::class.java]
}
Code in fragment:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//fragment receives the instance of MapViewModel
viewModel = ViewModelProviders.of(activity!!)[MapViewModel::class.java]
...
}
When I open the app for the first time, everything works fine: activity creates an instance of ViewModel; I open Fragment, which gets the instance of ViewModel. But when the application is trying to restore its state after being killed, first it calls the body of onCreate of the Fragment and then the body of onCreate of the Activity. At that point, the fragment can't get the ViewModel as Activity had not created it yet.
Solution 1: Move the code when the fragment gets the ViewModel from onCreate to onViewCreated. This is fine as I observe all live data in onViewCreated as well.
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = activity?.run { ViewModelProviders.of(this)[MapViewModel::class.java] } ?: throw Exception("Invalid Activity")
viewModel.getSurveyDateLiveData().observe(viewLifecycleOwner, Observer<String> { dateTextView.text = it })
...
}
Solution 2:
Create the instance of ViewModel in Activity.onCreate before super.onCreate is called. In this case, you can get the ViewModel in your fragment's onCreate.
override fun onCreate(savedInstanceState: Bundle?) {
val factory = App.get().components().appComponent.getMapViewModelFactory()
viewModel = ViewModelProviders.of(this, factory)[MapViewModel::class.java]
super.onCreate(savedInstanceState)
Timber.d("cc: onCreate: $this ")
}
Solution 3:
If you are injecting repository instance in your ViewModel, Check that you are not using #Inject constructor(...): ViewModel() to inject your repository, but rather **#ViewModelInject constructor(...): ViewModel()**
I fixed the same problem by doing this.
Note:- I am using Dagger hilt, Room database, MVVM, Data binding
Added the annotation.
class AlertViewModel
#Inject
constructor(private val userRepository: AlertRepository) : ViewModel(){
val getList:LiveData<List<Alert>> get() =
userRepository.getList.flowOn(Dispatchers.Main)
.asLiveData(context = viewModelScope.coroutineContext)
fun insert(user:Alert){
viewModelScope.launch {
userRepository.insert(user)
}
}
}
To
#HiltViewModel // Added this annotation
class AlertViewModel
#Inject
constructor(private val userRepository: AlertRepository) : ViewModel(){
val getList:LiveData<List<Alert>> get() =
userRepository.getList.flowOn(Dispatchers.Main)
.asLiveData(context = viewModelScope.coroutineContext)
fun insert(user:Alert){
viewModelScope.launch {
userRepository.insert(user)
}
}
}
I got this after migrating to AndroidX.
There's a bug in androidx.lifecycle:lifecycle-viewmodel:2.0.0-beta01 where Proguard removes the constructor.
https://issuetracker.google.com/issues/112230489
Fix by upgrading to 2.0.0, and remember to update your proguard rules if needed.
My error message looked like this:
java.lang.RuntimeException: Cannot create an instance of class my.custom.viewmodel.CustomViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:202)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:135)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:103)
......
Caused by: java.lang.NoSuchMethodException: <init> [class android.app.Application]
at java.lang.Class.getConstructor0(Class.java:2204)
at java.lang.Class.getConstructor(Class.java:1683)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:200)
... 34 more
androidx.test.espresso.PerformException: Error performing 'single click - At Coordinates: 539, 1167 and precision: 16, 16' on view 'with id: my.test:id/button_return_to_main_menu'.
at androidx.test.espresso.PerformException$Builder.build(PerformException.java:82)
at androidx.test.espresso.base.DefaultFailureHandler.getUserFriendlyError(DefaultFailureHandler.java:79)
.....
Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{my.custom.domain.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class my.custom.viewmodel.CustomViewModel
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
if your PostViewModel class is an inner class, make sure its public and static
Please add below code. It worked for me
val binding = FragmentLayoutBinding.inflate(inflater, container, false)
val viewModel = ViewModelProvider(
requireActivity(),
defaultViewModelProviderFactory
).get(MainViewModel::class.java)
If you face this issue in Kotlin Dagger Hilt even after #HiltViewModel and using #Inject, make sure you have updated all hilt dependencies.
In my case I needed to use a ListItemViewModelFactory to pass in a parameter to my view model.
In my case, it was gradle a dependencies problem.
If you are using Livedata,,
build.gradle(Module.app)
not
implementation 'android.arch.lifecycle:extensions:1.1.1'
kapt 'android.arch.lifecycle:common-java8:1.1.1'
use these
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
kapt 'androidx.lifecycle:lifecycle-common-java8:2.2.0'
If you're using Hilt Dependency Injection, You probably have missed #ViewModelInject. Because, Hilt provide its own injection for viewmodel.
In my case, I used and #Inject due to this caught into the error.
I had a different scenario when creating a view model instance:
I was requesting for the instance in a fragment.
My ViewModel required a parameter to be passed on the constructor.
I was not using Dependency Injection.
Solution
In a scenario where your viewmodel requires a parameter to be passed you have to create a ViewModelFactory to define your instances
Solution In Practice
- ViewModel Sample
class SharedViewModel(private val repository: UserRepository) : ViewModel() {
init {
viewModelScope.launch {
repository.refreshDataInDb()
}
}
}
- Creating ViewModel Factory
class ViewModelFactory(
private val repository: UserRepository
) : ViewModelProvider.NewInstanceFactory(){
override fun <T : ViewModel> create(modelClass: Class<T>): T {
return SharedViewModel( repository as UserRepository) as T
}
}
- Creating ViewModel Instannce in a Fragment
private lateinit var factory: ViewModelFactory
private lateinit var searchViewModel: SharedViewModel
private lateinit var repository: UserRepository
repository = UserRepository()
factory = ViewModelFactory(repository)
searchViewModel = ViewModelProvider(requireActivity(), factory)[SharedViewModel::class.java]
My problem was that the IDE had added a "abstract" modifier to my ViewModel class.
Make ViewModal class and constructure public
If constructor of your viewmodel is public and accepts only application then make sure you can create your own model without ViewModelProvider. Error message might be much more clear:
val model = YouViewModel(app)
I'm a proficient Android developer and I have used ViewModel 100s of times with no issue. Today I came across this issue. Spent hours and scrolled through various SO posts. Didn't get solved.
Then I saw that the package name in which I have the ViewModel contains new. Like this:
com.myapp.myfeature.new.feature
I changed new to neww for testing like this:
com.myapp.myfeature.neww.feature
and it worked! I hope someone find it useful.
If you are using version 2.33-beta and upper remove these dependencies;
implementation "androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha03"
kapt "androidx.hilt:hilt-compiler:1.0.0-beta01"
Keep only these two dependency
implementation "com.google.dagger:hilt-android:2.33-beta"
kapt "com.google.dagger:hilt-android-compiler:2.33-beta"