How to get an Instance of ViewModel in activity in 2020/21?

Question

I am new to the mvvm pattern. I created a ViewModel for the main activity. Now I want to get an instance of the ViewModel in the main activity.

Most Tutorials and answers here on Stackoverflow suggest using ViewModelProviders.of(..., but this is depreceated.

So according to this question on stackoverflow: ViewModelProviders is deprecated in 1.1.0 main activity in onCreate, I do the following (and I could swear I already had it running): mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);

However, I am getting an error telling me, that no suitable constructor has been found.

error: no suitable constructor found for ViewModelProvider(MainActivity)

Alternatively to make absolutely clear, that the MainActivity shall be the ViewModelStoreOwner, I created a variable ViewModelStoreOwner vmso = this; and put that variable into the constructor like so: mainActivityViewModel = new ViewModelProvider(vmso).get(MainActivityViewModel.class);

are you sure your reference to `this` is correct? If it's a Fragment you'll need to use `getActivity()` instead of `this` iirc, and if you are in a listener or anonymous class you will have to do `MainActivity@this` etc etc — Blundell, Jan 28 '20 at 16:22
Does this answer your question? [As ViewModelProviders.of() is deprecated, How should i create object of ViewModel?](https://stackoverflow.com/questions/57534730/as-viewmodelproviders-of-is-deprecated-how-should-i-create-object-of-viewmode) — Chisko, Jan 30 '20 at 18:14
No, it doesn not. The described solution in Java code is ```boardViewModel = new ViewModelProvider(this).get(BoardViewModel.class)```, which is equivalent to ```mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);``` which I already tried, but seems to be no suitable constructor. — Gerke, Jan 31 '20 at 15:07

score 28 · Accepted Answer · answered Apr 03 '20 at 11:58

You should update your gradle file to:

implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

And due to this change you can pass Activity to the constructor you mentioned:

mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);

score 9 · Answer 2 · answered Jul 23 '20 at 19:16

Using Fragment-ktx libr in your app you can get viewModel as below

First Update Gradle File as app -> build.gradle

implementation 'androidx.fragment:fragment-ktx:1.1.0'

// get ViewModel in Activity or Fragment as

private val viewModel: MainActivityViewModel by viewModels()

// If you want to get same instance of ViewModel in ChildFragment as

 private val viewModel: MainActivityViewModel by viewModels(
    ownerProducer = { requireParentFragment() }
)

Fragment-ktx is for fragments. We need **activity-ktx** – IgorGanapolsky Apr 22 '21 at 01:29 — IgorGanapolsky, Apr 22 '21 at 01:29

Boy · Answer 3 · 2020-12-01T15:03:55.160

7

Use val viewModel by viewModels<TheViewModel>() in Activities and val viewModel by activityViewModels<TheViewModel>() in fragment to obtain the same viewmodel from the activity (so sharing the viewmodel).

This is part of androidx now

edited Dec 01 '20 at 15:03

answered Sep 24 '20 at 07:36

Boy

5,006
4
47
60

1

Thanks! This is probably obvious to most people, but you can also do `val viewModel: ThisViewModel by viewModels()` and `val viewModel: ThisViewModel by activityViewModels()` – eddielement Apr 15 '21 at 02:20

score 2 · Answer 4 · answered Feb 01 '20 at 17:22

2

For now, the only thing working for me was to use: MainActivityViewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MainActivityViewModel.class);

However, I am still thankful for any advice, how this can be done different using new ViewModelProvider(this).get(MainActivityViewModel.class);

answered Feb 01 '20 at 17:22

Gerke

437
1
4
15

This still fails, but this time with `java.lang.RuntimeException: Cannot create an instance of class xxx` instead – Davide Mar 23 '20 at 20:44
Did you follow the first answer ? – Ahmed Elsayed Aug 31 '20 at 08:57

score 2 · Answer 5 · answered Sep 29 '20 at 21:06

2

Get ViewModel In New Way

MainActivityViewModel mainActivityViewModel;
    mainActivityViewModel= new ViewModelProvider(this).get(MainActivityViewModel.class);

answered Sep 29 '20 at 21:06

Ali Raza

101
1
6

This is Java. We use Kotlin. – IgorGanapolsky Apr 22 '21 at 01:31

score 0 · Answer 6 · answered Jan 30 '20 at 17:59

0

Duplicate question and already answered here

Simply replace:

This:

boardViewModel = ViewModelProviders.of(this).get(BoardViewModel::class.java)

With this:

boardViewModel = ViewModelProvider(this).get(BoardViewModel::class.java)

answered Jan 30 '20 at 17:59

Devara

69
2

5

If this question is a duplicate, please refrain from answering and flag as so instead – Chisko Jan 30 '20 at 18:14
Plus, your suggestion does not work but fails with `error: no suitable constructor found for ViewModelProvider(MainActivity)` as described in the question – Davide Mar 23 '20 at 20:43
main thing to notice here is the line that we need to replace is ViewModelProvider not ViewModelProviders. notice the 's' here at the end. – Ravi Yadav Sep 23 '20 at 18:05

score 0 · Answer 7 · edited Jul 15 '20 at 06:57

You can use a ViewModelFactory:

val viewModelFactory = VMFactory(requireActivity().application)
viewModel= ViewModelProvider(requireActivity(),viewModelFactory).get(MainViewModel::class.java)

VMFactory code:

class VMFactory(application: Application) : ViewModelProvider.NewInstanceFactory() {

    val _application: Application=application

    @NonNull
    override fun <T : ViewModel?> create(@NonNull modelClass: Class<T>): T {
            return  MainViewModel(_application) as T
    }
}

Please note that here my MainViewModel extends AndroidViewModel and hence requires application as the input parameter.

score 0 · Answer 8 · answered Dec 27 '20 at 09:18

I had similar problems and in the end found out I missed off the "extends ViewModel" within the class definition, so it should look like this:

public class ViewModelClass extends ViewModel
{
    // Tracks the score for Team A
    public int scoreTeamA = 0;

    // Tracks the score for Team B
    public int scoreTeamB = 0;
}

score -1 · Answer 9 · answered Jan 28 '20 at 18:02

-1

ViewModel viewModel = ViewModelProviders.of(this).get(ViewModel.class);

Android Support library version is depreciated. So you need to make sure that you import Androidx. And you need to implement androidx dependency in Gradle file.

It is not advised to create a new ViewModel object with "new" keyword.

answered Jan 28 '20 at 18:02

barutto

94
1
14

2

According to the developer guides, ViewModelProviders is depreceated and it is recommended to use the constructors directly. https://developer.android.com/reference/androidx/lifecycle/ViewModelProviders.html – Gerke Jan 28 '20 at 20:48

How to get an Instance of ViewModel in activity in 2020/21?

9 Answers9

First Update Gradle File as app -> build.gradle

Linked