CODEWITHSUNDEEP
androidmvvmandroid-roomandroid-viewmodel
Sakshi Gupta
Sakshi Gupta

Reputation: 116

Activity with multiple live data objects

I have a table, containing list of cards, in my room db. I have 2 recycler view in my fragment. Need to populate these recycler views basis on card ids. Whenever there is a change in this table, live data gives callback to both the recycler view. Instead I want if that particular card d is updated, only then live data updates my UI. Right now, if any id data is updating, I am getting callback to both the recycler views. For example, if d passed is "Sbi", then if there is a change in sbi data row, only update first recycler view not the second recycler view. Also if passed id is "sbi", then ignore updates in other ids for now.

ACTIVITY

@Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
myViewModel = ViewModelProviders.of(this).get(MyViewModel.class);

myViewModel.getFirstData("Sbi")).observe(this,
                result -> {
                    myFirstAdapter.addList(result);
                });

myViewModel.getSecondData("Sbi1").observe(this,
                result -> {
                    mySecondAdapter.addList(result);
                });
}

MyViewModel

public LiveData<List<MyModel>> getFirstData(String cardId) {
        return myDao.getItems(cardId);
    }

public LiveData<List<MyModel>> getSecondData(String cardDetailId) {
        return myDao.getItems(cardDetailId);
    }

Upvotes: 0

Views: 65

Answers (1)

sergiy tykhonov
sergiy tykhonov

Reputation: 5103

  1. When you use Room with LiveData - under the hood Room-framework generates some low-level boiler-plate code that is responsible for invoking that magic "callback" when there is some change in table. It looks like a:

    mObserver = new InvalidationTracker.Observer(tableNames) {...

According to documentation this method "adds the given observer to the observers list and it will be notified if any table it observes changes". As I understand Room doesn't switch on some "smart-mode" where it analyse parameters of specific query (with "where id:= ..." in your case) and it invokes your observe-LiveData-callbacks whenever table changes, no matter what id you mentioned in your LiveData-function. In other words, if you use Room, you'll give both observe-callbacks with every change in associated sqlite-table.

  1. If your RecyclerViewAdapter is using DiffUtils (if is not using, start do that) then you'll have no troubles with regular updating RecyclerView. Actually there will be no updating because list of data isn't changed.

Upvotes: 1

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