user-mw

public class Activity {

  // Code
  
  public Object onRetainNonConfigurationInstance() {
    return null;
  }
  
  // Code
}

user-mw

public class FragmentActivity {

  @Override
  @Nullable
  public final Object onRetainNonConfigurationInstance() {
    // Code
    NonConfigurationInstances nci = new NonConfigurationInstances();
    // Code
    nci.viewModelStore = mViewModelStore;
    return nci;

user-mw

public class FragmentActivity {
  // Code
  public Object getLastCustomNonConfigurationInstance() {
    NonConfigurationInstances nc = (NonConfigurationInstances)
           getLastNonConfigurationInstance();
    return nc != null ? nc.custom : null;
  }

  public Object onRetainCustomNonConfigurationInstance() {
    return null;

user-mw

public class Fragment {

  // Code
  
  public ViewModelStore getViewModelStore() {
    // Code

    if (mViewModelStore == null) {
      mViewModelStore = new ViewModelStore();
    }

user-mw

public final Object onRetainNonConfigurationInstance() {
        // Code

        FragmentManagerNonConfig fragments = mFragments.retainNestedNonConfig();
  
        // Code
        NonConfigurationInstances nci = new NonConfigurationInstances();
        nci.custom = custom;
        nci.viewModelStore = mViewModelStore;
        nci.fragments = fragments;

user-mw

final class FragmentState implements Parcelable {
  // Code
  
  public Fragment instantiate(FragmentHostCallback host, FragmentContainer container,
            Fragment parent, FragmentManagerNonConfig childNonConfig,
            ViewModelStore viewModelStore) {
  
        // Code, that initialize a new Fragment 
            
        mInstance.mViewModelStore = viewModelStore;

user-mw

public abstract class ViewModel {

   protected void onCleared() { // Code }

   final void clear() { // Code }

   <T> T setTagIfAbsent(String key, T newValue) { // Code }

   <T> T getTag(String key) { // Code }

user-mw

public class Fragment {
  // Code
  public ViewModelStore getViewModelStore() {
    if (mFragmentManager == null) {
       throw new IllegalStateException(// Exception text);
    }
    return mFragmentManager.getViewModelStore(this);
  }
 // Code
}

user-mw

public class FragmentManagerImpl {

  // Code
  
  ViewModelStore getViewModelStore(@NonNull Fragment f) {
    return mNonConfig.getViewModelStore(f);
  }
  
  // Code
}

user-mw

final class FragmentManagerImpl extends FragmentManager implements LayoutInflater.Factory2 {
  // Code
  public void attachController(@NonNull FragmentHostCallback host,
            @NonNull FragmentContainer container, @Nullable final Fragment parent) {
        // Code
        if (parent != null) {
            // Code
        } else if (host instanceof ViewModelStoreOwner) {
            ViewModelStore viewModelStore = ((ViewModelStoreOwner) host).getViewModelStore();
            mNonConfig = FragmentManagerViewModel.getInstance(viewModelStore);