Viewmodel Livedata不会更新数据观察者

Question

For example, I have 12 UpcomingGamesFragment and each fragment has a different set of game data releasing a month, for example the first fragment of 12 will have video games releasing on January 2019.

In my app, there's a navigation drawer with a list of platforms (ps4, xbox, pc, etc.) and when the user picks his consoles by clicking on the check boxes and then closes the drawer layout, I want all the fragments to update accordingly. Like only show games releasing on these platforms. Retrieve and filter successfully works through a method in UpcomingGamesFragment called loadReleasesData()

Now what I want is all the fragments to update when the navigation drawer gets closed, because my implementation doesn't work, please tell me what's wrong.

Here's my ViewModel class:

public class ReleasesViewModel extends ViewModel {
    private MutableLiveData<List<_Release>> upcomingReleases = new MutableLiveData<>();

    public ReleasesViewModel() { }

    public MutableLiveData<List<_Release>> getUpcomingReleases() {
        return upcomingReleases;
    }
}

And in my Filter drawer layout is in my MainActivity, and also I declare my ViewModel in my MainActivity:

OnCreate (A lot of code omitted for clarity)

mReleasesViewModel = ViewModelProviders.of(this).get(ReleasesViewModel.class);

My drawer layout on close:

@Override
public void onDrawerClosed(@NonNull View drawerView) {
    // If change detected refresh!
    if (!mCopyOfUserPlatforms.equals(SharedPrefManager.read(SharedPrefManager.PLATFORM_IDS, mDefaultPlatformsSet))) {
        mReleasesViewModel.getUpcomingReleases().setValue(new ArrayList<_Release>());
    }
}

And I pass the viewmodel livedata object to my 12 fragments when I initialize them in another fragment called the ViewPagerFragment here's how:

onCreateView:

   // Get the ViewModel
    ReleasesViewModel releasesViewModel = ((MainActivity)getActivity()).mReleasesViewModel;
    for (int i = 0; i < 14; i++) {
        UpcomingGamesFragment upcomingGamesFragment = new UpcomingGamesFragment();
        upcomingGamesFragment.setLiveData(releasesViewModel); // HERE 
        mSectionsPagerAdapter.addFragment(upcomingGamesFragment, title, queryId);
    }

This is my setLiveData() method in UpcomingGamesFragment:

public void setLiveData(ReleasesViewModel releasesViewModel) {
    releasesViewModel.getUpcomingReleases().observe(this, new android.arch.lifecycle.Observer<List<_Release>>() {
        @Override
        public void onChanged(@Nullable List<_Release> releases) {
            Log.d(TAG, "Refreshing this baby boy...");
            loadReleaseData(0);
        }
    });
}

How I know the livedata doesn't update all my fragments? It is because I have a log in my loadReleasesData method and it doesn't get printed in the Logcat and not to mention the fact it doesn't update the fragment(s). Have a good day and bye! :)

Answer 1

Your issue is not with LiveData but with ViewModel instance you're getting in ViewPagerFragment :

use this in your onCreateView() of fragment:

ReleasesViewModel releasesViewModel = ViewModelProviders.of(getActivity()).get(ReleasesViewModel.class);

instead of your code:

// Get the ViewModel
ReleasesViewModel releasesViewModel = ((MainActivity)getActivity()).mReleasesViewModel;