Convert LiveData to MutableLiveData

Question

Apparently, Room is not able to handle MutableLiveData and we have to stick to LiveData as it returns the following error:

error: Not sure how to convert a Curso         


        

Answer 1

Since Room doesn't support MutableLiveData and has support for LiveData only, your approach of creating a wrapper is the best approach I can think of. It will be complicated for Google to support MutableLiveDatasince the setValue and postValue methods are public. Where as for LiveData they are protected which gives more control.

Answer 2

In your repository you can get LiveData and transform it to MutableLivedata:

var data= dao.getAsLiveData()
return MutableLiveData<T>(data.value)

Answer 3

Call me crazy but AFAIK there is zero reason to use a MutableLiveData for the object that you received from the DAO.

The idea is that you can expose an object via LiveData<List<T>>

@Dao
public interface ProfileDao {
    @Query("SELECT * FROM PROFILE")
    LiveData<List<Profile>> getProfiles();
}

Now you can observe them:

profilesLiveData.observe(this, (profiles) -> {
    if(profiles == null) return;

    // you now have access to profiles, can even save them to the side and stuff
    this.profiles = profiles;
});

So if you want to make this live data "emit a new data and modify it", then you need to insert the profile into the database. The write will re-evaluate this query and it will be emitted once the new profile value is written to db.

dao.insert(profile); // this will make LiveData emit again

So there is no reason to use getValue/setValue, just write to your db.

Answer 4

If you really need to, then you can use the mediator trick.

In your ViewModel

 val sourceProduct: LiveData<Product>() = repository.productFromDao()
 val product = MutableLiveData<Product>()

 val mediator = MediatorLiveData<Unit>()

 init {
      mediator.addSource(sourceProduct, { product.value = it })
 }

In fragment/activity

observe(mediator, {})
observe(product, { //handle product })