'Cannot create an instance of class ViewModel

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;
    }
}

Solution 1:^[1]

Make your constructor public.

Solution 2:^[2]

if you are using Hilt, ensure your activity/fragment is having @AndroidEntryPoint annotation

Solution 3:^[3]

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

Solution 4:^[4]

Make sure your ViewModel has constructor with only one parameter i.e. Application.

example:

public YourViewModel(Application application) {
    super(application);
    ...

Solution 5:^[5]

DggerHilt can also be the reason, If you are using it make sure your activity/fragment is having @AndroidEntryPoint annotation on it.

Solution 6:^[6]

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'

Solution 7:^[7]

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

Solution 8:^[8]

Add @HiltViewModel on top of your viewModel .

Solution 9:^[9]

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() {}

Solution 10:^[10]

Make the class and constructor public it solved my problem .

Solution 11:^[11]

Extend AndroidViewModel from your ViewModel class.

public class YourViewModel extends AndroidViewModel {

    public YourViewModel(Application application) {
        super(application);

        //Todo: ...
    }

}

Solution 12:^[12]

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.

Solution 13:^[13]

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

Solution 14:^[14]

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.

Solution 15:^[15]

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

Solution 16:^[16]

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()**

Solution 17:^[17]

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)

Solution 18:^[18]

if your PostViewModel class is an inner class, make sure its public and static

Solution 19:^[19]

Please add below code. It worked for me

val binding = FragmentLayoutBinding.inflate(inflater, container, false)

val viewModel = ViewModelProvider(
            requireActivity(),
            defaultViewModelProviderFactory
            ).get(MainViewModel::class.java)

Solution 20:^[20]

If you face this issue in Kotlin Dagger Hilt even after @HiltViewModel and using @Inject, make sure you have updated all hilt dependencies.

Solution 21:^[21]

In my case I needed to use a ListItemViewModelFactory to pass in a parameter to my view model.

Solution 22:^[22]

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'

Solution 23:^[23]

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.

Solution 24:^[24]

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)
        }
    }
}

@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)
        }
    }
}

Solution 25:^[25]

My problem was that the IDE had added a "abstract" modifier to my ViewModel class.

Solution 26:^[26]

Make ViewModal class and constructure public

Solution 27:^[27]

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)

Solution 28:^[28]

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.

Solution 29:^[29]

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"

Solution 30:^[30]

For ViewModels used with Jetpack Compose

In case you are using Jepack Compose with a ViewModel in your component. The @Preview annotation may cause this error. That was the problem in my case.

Hope it helps someone!

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	CommonsWare
Solution 2
Solution 3	Max
Solution 4	vivek
Solution 5	Rahul
Solution 6
Solution 7	Ali Zarei
Solution 8	Rabindra Khadka
Solution 9	Brandon
Solution 10	RaghavPai
Solution 11	Zeero0
Solution 12	Duncan Lukkenaer
Solution 13	Afjalur Rahman Rana
Solution 14	lomec
Solution 15	iamkdblue
Solution 16	Rahul
Solution 17	Lydia Ralph
Solution 18	Lasitha Lakmal
Solution 19	Evgeniy Mishustin
Solution 20	Abdul Mateen
Solution 21	Loren
Solution 22	J.Dragon
Solution 23	Sohail Pathan
Solution 24	Quick learner
Solution 25	DBragion
Solution 26	John Ruban Singh
Solution 27	eleven
Solution 28	Paras Sidhu
Solution 29	Ahmet B.
Solution 30	Omar El Hussein

'Cannot create an instance of class ViewModel

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Solution 4:[4]

Solution 5:[5]

Solution 6:[6]

Edited

Solution 7:[7]

Solution 8:[8]

Solution 9:[9]

Solution 10:[10]

Solution 11:[11]

Solution 12:[12]

For people using Jetpack Compose, Navigation and Hilt

Solution 13:[13]

Solution 14:[14]

Solution 15:[15]

Solution 16:[16]

Solution 17:[17]

Solution 18:[18]

Solution 19:[19]

Solution 20:[20]

Solution 21:[21]

Solution 22:[22]

Solution 23:[23]

Solution 24:[24]

Solution 25:[25]

Solution 26:[26]

Solution 27:[27]

Solution 28:[28]

Solution 29:[29]

Solution 30:[30]