Firebase Retrieve Data Null Outside Method

Retrieve data from firebase return null in onCreateView

Move your code inside onDataChange as Firebase fetches data asynchronously

databaseTracks.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Iterable<DataSnapshot> children = dataSnapshot.getChildren();

            if (trackList != null) {
                trackList.clear();
            }

            for (DataSnapshot c : children) {
                trackList.add(c.getValue(UserFoodRecord.class));
            }

            if (trackList != null) {
                for (UserFoodRecord u : trackList) {
                    dateList.add(u.getDate());
                    if (u.getDate() == todayDate) {
                        checkTodayRecord = true; //got today record
                        UserFoodRecord tempRecord = new UserFoodRecord(u.getDate(), u.getBreakfast(), u.getLunch(), u.getDinner(), u.getOther()
                                , u.getExercise(), u.getGoal(), u.getFood(), u.getExerciseBurn());
                        currentUserFoodRecord = tempRecord;
                    }
                }
            }

            if (currentUserFoodRecord != null) {
                caloriesGoal.setText(currentUserFoodRecord.getGoal().toString());
                caloriesFood.setText(currentUserFoodRecord.getFood().toString());
                caloriesExerc.setText(currentUserFoodRecord.getExerciseBurn().toString());
                caloriesRemain.setText(currentUserFoodRecord.getRemaining().toString());
            }

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

I get null when I try to access a variable from inner class in firebase methods

You cannot use something now that hasn't been loaded yet. With other words, you cannot simply use the username outside the onDataChange() method because it will always be null due the asynchronous behaviour of this method. This means that by the time you are trying to print that result outside that method, the data hasn't finished loading yet from the database and that's why is not accessible.

A quick solve for this problem would be to use that results only inside the onDataChange() method, otherwise I recommend you see the last part of my anwser from this post in which I have explained how it can be done using a custom callback. You can also take a look at this video for a better understanding.

String returns null after leaving child, when retrieving from firebase

That's because of async execution of the code, to fix it you'll have to wait for the execution. Like this:

void getData(String name, String dataToFetch) async{ // NOTE THE ASYNC HERE
    //use await to wait for async execution
    String value = await DBRef.child("dataToFetch").once().then((DataSnapshot dataSnapShot){
         name = dataSnapShot.value;
         print("one $name");
         return name;
   });
   print("two $value");
  }

UPDATE
If you call this method from the state of a StatefullWidget this is how you should implement it:

class _MyHomePageState extends State<MyHomePage> {
  String name; // this property will be updated by the getData

  @override
  void initState() {
    super.initState();
    getData(name, "theKeyYouWant"); // call getData in init state
  }

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Test App'),
      ),
      body: Text(name)
    );
  }

  void getData(String paramName, String dataToFetch) async {
    DBRef.child("dataToFetch").once().then((DataSnapshot dataSnapShot){
      setState(() { // this will trigger the build method
        name = dataSnapShot.value;  // we update the new value.
      });
    });
  }

}

Firebase - retrieving data by value to an outside variable

Firebase use callback methods to get the data from the server, In your case the return statement will be executed before the callback come from the Firbase. You can try to pass a callback method to your function and execute that when the callback from Firebase is triggered.

public static void checkIfBookmarked(final String title, callbackFunction){
    final FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
    final DatabaseReference userBookmarks = FirebaseDatabase.getInstance().getReference().child("users")
            .child(user.getUid()).child("bookmarks");
    final boolean[] exists = new boolean[1];
    userBookmarks.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            exists[0] = dataSnapshot.child(title).exists() ;
            //execute your callback function here
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
    return;
}

Check this to see how to pass a function as parameter.
Passing function as a parameter in java

An alternative would be to move your code into OnDataChange method

---

Related Topics