android mvvm and livedata: list not observed in activity - mvvm

Question

I am developing an android app that has an activity with a recyclerview and an add button. When add button is clicked, a FragmentDialog is launched. the user enters the name of the book which will be stored in a greendao database. The list of books is displayed in the recyclerview.
I am using mvvm and livedata . the problem is that after adding the book in DialogFragment, the list is not updated, although the list is wrapped in livedata which is observed in activity.
DialogFragment:
// repository
val repository = Injection.provideRepository()
// viewmodel
val factory = CreateBookViewModelFactory(repository)
val viewModel =
ViewModelProvider(this, factory).get(BookViewModel::class.java)
builder.setView(binding.root)
// Add action buttons
.setPositiveButton(R.string.add,
DialogInterface.OnClickListener { dialog, id ->
// create book
book = Book(null, binding.name)
viewModel.onAddBook(book)
})
.setNegativeButton(R.string.cancel,
DialogInterface.OnClickListener { dialog, id ->
getDialog()?.cancel()
})
builder.create()
} ?: throw IllegalStateException("Activity cannot be null")
}
}
viewModel:
class BookViewModel(val repository: Repository) : ViewModel() {
// Create a LiveData
val _books = MutableLiveData<List<Book>>()
val books = repository.books
fun init() :MutableLiveData<List<Book>> {
_books.postValue(books)
return _books
}
}
activity
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = DataBindingUtil.setContentView(this, R.layout.activity_books)
binding.setLifecycleOwner(this)
binding.recyclerview.adapter = adapter
binding.recyclerview.setHasFixedSize(false)
// repository
val repository = Injection.provideRepository()
val factory = CreateBookViewModelFactory(repository)
val viewModel =
ViewModelProvider(this, factory).get(BookViewModel::class.java)
viewModel.init().observe(this, Observer {
it?.let {
adapter.submitList(Mapper.mapToBookListDTO(it))
}
})
binding.addReturn.setOnClickListener { view ->
val createFragment: DialogFragment = BookDialog()
createFragment.show(supportFragmentManager, "new Book")
}
}
When I add a new book and click the add button, the list is not updated. But when I reopen the activity the list of books get updated, it means the list is not observed for changes.
I am using the same viewModel for the activity and the DialogFragment. I also tried using seperate viewmodels for each, but same result.
Thanks a lot for your help!