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);

Answer 1

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); 

Answer 2

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() } )