SavedStateViewModelFactory.java

@NonNull
@Override
public <T extends ViewModel> T create(@NonNull String key, @NonNull Class<T> modelClass) {
  boolean isAndroidViewModel = AndroidViewModel.class.isAssignableFrom(modelClass);
  ...
  Constructor<T> constructor;
  constructor = ... // Define ViewModel Constructor
  // Case 1, SavedStateHandleが不要の場合
  if (constructor == null) {
    return mFactory.create(modelClass);
  }
  // Case 2, SavedStateHandleが必要な場合
  SavedStateHandleController controller = SavedStateHandleController.create(
      mSavedStateRegistry, mLifecycle, key, mDefaultArgs);
  try {
    T viewmodel;
    // SavedStateHandleControllerを介してSavedStateHandleを注入
    if (isAndroidViewModel) {
      viewmodel = constructor.newInstance(mApplication, controller.getHandle());
    } else {
      viewmodel = constructor.newInstance(controller.getHandle());
    }
    ...
    return viewmodel;
  }
  ...
}