将数据发送到另一活动的一个活动的片段？

Question

I have MainActivity which contains TabLayout with tabs: each tab is a fragment and each one has a RecyclerView. When I tap FAB in Main Activity, NewReminderActivity is opened.

I use Architecture Components: Entity(Reminder), DAO, Room, ViewModel, LiveData and Repository.

The question is:

• Which methods should I use to deliver a new created reminder item into the fragment (which contains as mentioned above a RecyclerView?

I have some ideas, but could you help me please and give me a right direction for implementing:

1) I guess, I should deliver data to MainActivity, then from MainActivity to the fragment and use ViewModel as mentioned in https://developer.android.com/topic/libraries/architecture/viewmodel.html#sharing , am I right?

2) I guess I should use setResult() in NewReminderActivity, am I right?

Answer 1

If you are using Room, there is no reason for you to use setResult to transfer new item to any of these previous Fragments/Activities, because Room manages invalidation automatically.

@Dao
public interface MyDao {
    @Query("SELECT * FROM ITEM")
    LiveData<List<Item>> getItemsWithChanges();

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertItem(Item item);
}

Then

public class MyViewModel extends ViewModel {
    private final LiveData<List<Item>> items;

    public LiveData<List<Item>> getItems() {
        return items;
    }

    public MyViewModel(MyDao myDao) {
        items = myDao.getItemsWithChanges();
    }
}

Then

public class MyFragment extends Fragment {
    MyViewModel myViewModel;

    @Override
    protected void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        myViewModel = ViewModelProviders.of(getActivity(), viewModelFactory).get(MyViewModel.class);
        myViewModel.getItems().observe(getViewLifecycleOwner(), (items) -> {
            if(items != null) {
                adapter.submitList(items);
            }
        });
    }
}

In which case all you need to do in your second Activity is insert the new item, then finish out:

// imagine this is on background thread
myDao.insertItem(item);
runOnUiThread(() -> {
    finish();
});

And all your RecyclerViews will update with the new item (if they are part of the results as the condition matches it).