Why is the Android viewModels() extension function available in the fragment-ktx instead of viewmodel-ktx library?

Question

When I use viewModels() as below

class MainActivity : AppCompatActivity() {

    private val viewModel: MainViewModel by viewModels()

    // ... more codes
}

Why is it available in

implementation 'androidx.fragment:fragment-ktx:1.3.0'

Instead, when I include things like below, it is not available in them?

implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.3.0'
implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.0'
implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

I thought it supposed to be in the viewmodel-ktx library instead of fragment-ktx library

Answer 1

As per the documentation, the by viewModels() extension is an extension on the Fragment class and therefore, must belong in the fragment-ktx artifact - the lifecycle-viewmodel-ktx and lifecycle-runtime-ktx do not have any dependency on fragments and the lifecycle-extensions artifact is completely deprecated and should not be used at all as per the Lifecycle 2.2.0 release notes.