Assigning value to a global variable from FirebaseDatabase

Question

I want to know that is it possible to assign value to a global variable using FirebaseDatabase methods. I know that the FirebaseDatabase methods are asynchronous and executed in background without blocking the main thread. But I am stuck in a case where the value is needed outside the onDataChange() method. Here is my java class file:

public class DetailActivity extends YouTubeBaseActivity implements YouTubePlayer.OnInitializedListener {

private ProgressBar mProgressBar;
private CoordinatorLayout coordinatorLayout;

private static final int RECOVERY_DIALOG_REQUEST = 1;
YouTubePlayerView youTubePlayerView;

int currentPage = 0;
Timer timer;
final long DELAY_MS = 500;
final long PERIOD_MS = 3000;
CircleIndicator circleIndicator;
private ViewPager viewPager;
private PagerAdapter adapter;

private ArrayList<String> images;
private ArrayList<String> imageDetails;

private DatabaseReference databaseReference;

private TextView capital, area, population,languages,literacyRate;
private ImageView appbarImageView;
private ExpandableTextView historyTextView;

private String youTubeVideoLink;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_detail);
    CollapsingToolbarLayout collapsingToolbarLayout = findViewById(R.id.collapsing_toolbar);

    viewPager = findViewById(R.id.view_pager);
    circleIndicator = findViewById(R.id.indicator);
    mProgressBar = findViewById(R.id.progress_bar);

    youTubePlayerView =  findViewById(R.id.youtube_player_view);
    youTubePlayerView.initialize(BuildConfig.ApiKey, this);

    population = findViewById(R.id.population);
    capital = findViewById(R.id.capital);
    area = findViewById(R.id.area);

    coordinatorLayout = findViewById(R.id.detail_container);
    appbarImageView = findViewById(R.id.app_bar_image);
    historyTextView = findViewById(R.id.expand_text_view);
    literacyRate = findViewById(R.id.literacy_rate);
    languages = findViewById(R.id.languages);

    Intent intent = getIntent();
    if(intent.hasExtra("State")) {
        collapsingToolbarLayout.setTitle(intent.getStringExtra("State"));
        databaseReference = FirebaseDatabase.getInstance().getReference().child("States").child(intent.getStringExtra("State").trim());
    }



    final Handler handler = new Handler();
    final Runnable update = new Runnable() {
        @Override
        public void run() {
            if(currentPage == 12) {
                currentPage = 0;
            }
            viewPager.setCurrentItem(currentPage++,true);
        }
    };
    timer = new Timer();
    timer.schedule(new TimerTask() {
        @Override
        public void run() {
            handler.post(update);
        }
    },DELAY_MS,PERIOD_MS);
}

private void readDataFromDatabase(final StatesCallback statesCallback) {
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            StateDetails stateDetails = dataSnapshot.getValue(StateDetails.class);
            statesCallback.onCallback(stateDetails);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

@Override
protected void onDestroy() {
    super.onDestroy();
    timer.cancel();
}

@Override
public void onInitializationSuccess(YouTubePlayer.Provider provider, YouTubePlayer youTubePlayer, boolean b) {

    readDataFromDatabase(new StatesCallback() {
        @Override
        public void onCallback(StateDetails stateDetails) {
            mProgressBar.setVisibility(View.GONE);
            coordinatorLayout.setVisibility(View.VISIBLE);
            capital.setText(stateDetails.getCapital());
            area.setText(stateDetails.getArea());
            population.setText(stateDetails.getPopulation());
            historyTextView.setText(stateDetails.getHistory());
            languages.setText(stateDetails.getLanguages());
            literacyRate.setText(String.valueOf(stateDetails.getLiteracyRate()));
            images = stateDetails.getImages();
            imageDetails = stateDetails.getImageDetails();
            youTubeVideoLink = stateDetails.getYouTubeVideoLink();

            Log.i("youtube video",youTubeVideoLink);
            Picasso.get().load(images.get(0)).into(appbarImageView);
            adapter = new CustomAdapter(DetailActivity.this, images, imageDetails);
            viewPager.setAdapter(adapter);
            circleIndicator.setViewPager(viewPager);
            adapter.registerDataSetObserver(circleIndicator.getDataSetObserver());

        }
    });
    if(!b) {
        Log.i("Checking order","video link: "+youTubeVideoLink);
        youTubePlayer.cueVideo(youTubeVideoLink);
    }
}

@Override
public void onInitializationFailure(YouTubePlayer.Provider provider, YouTubeInitializationResult youTubeInitializationResult) {
    if(youTubeInitializationResult.isUserRecoverableError()) {
        youTubeInitializationResult.getErrorDialog(DetailActivity.this,RECOVERY_DIALOG_REQUEST);
    } else {
        String errorMessage = getString(R.string.youTubeErrorMessage)+youTubeInitializationResult;
        Toast.makeText(DetailActivity.this,errorMessage,Toast.LENGTH_SHORT).show();
    }

  }
}

Here's the log details:

I/Checking order: video link: null
I/youtube video: QR19-rUVjNQ

I want to assign a dynamic video to the YouTubePlayer who's link is stored in the database through the youTubeVideoLink string. I have tried the method listed here

But that didn't help. So,Is there any way so that the initialized youTubeVideoLink is sent to the onInitializationSuccess() method? Thank You.

Answer 1

You cannot simply create a global variable and use it's value outside the onDataChange() because this methos has an asynchronous behaviour. If you want to use a value that is coming from the database outside the onDataChange() method, you have two choices. The first one would be to pass the desired object as argument to a method that is defined in your class or, if you want it in a more complex way, then dive into the asynchronous world of modern API's and see the last part of my answer in this post, in which I have explained step by step how you can achieve this. For more information, you can take also a look at this video.

Edit:

databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        StateDetails stateDetails = dataSnapshot.getValue(StateDetails.class);
        methodThatDoesSomething(stateDetails); //Method call

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
});

private void methodThatDoesSomething(StateDetails stateDetails) {
    //Do what you need to do with your stateDetails object
}