Firebase datasnapshot.getValue() returns null

Question

In my app, I have used Firebase database and stored userID in a child and set the value of the child as username to get the username of the current user. Now I'm using addValueEventListener to get the username from the database. This is my Firebase structure.

The code is given below.

checkUsername.child("check").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                currentUser = dataSnapshot.child(getUserID()).getValue(String.class);
                Log.d(TAG, "onDataChange: currentUser = " + currentUser);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

While debugging, String currentUser returns null.

Screenshot of debugged answer.

`addValueEventListener` used if one object but here there are two you should use `ChildEventListener` to get them — Ahmed Abdelmeged, Aug 23 '17 at 11:24
getUserId() is a method that returns the String value of user id... — Simon, Aug 23 '17 at 11:33
please check if you are getting correct value from `getUserId()` — Atif Farrukh, Aug 23 '17 at 11:42
I have checked. It's returning the correct userId of the user. — Simon, Aug 23 '17 at 11:44

harshithdwivedi · Answer 1 · 2017-08-23T11:53:30.103

1

Since you have added the valueEventListener at the check node, so getting the child again makes no sense (Because the User ID is the key of check node and not a separate child).

Instead try calling dataSnapshot.getChildren(); directly to get the entire list of updated data and iterate through it to get whatever key value you need.

Something like this,

checkUsername.child("check").addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {
       String current value = dataSnapshot.getValue(String.class); 
        Log.d("TAG", "onDataChange: " + current value);
    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {}

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {}

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {}

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

Another option in this particular use case is to add a ChildEventListener and get the value inside onChildAdded() method.

edited Aug 23 '17 at 11:53

answered Aug 23 '17 at 11:29

harshithdwivedi

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Check the updated answer and the screenshot. It still returns null. – Simon Aug 23 '17 at 11:39
I should have typed `ds` instead of `datasnapshot` there but I have checked, even it was `ds` it still returns null. – Simon Aug 23 '17 at 11:43
@Simon Directly call `ds.getValue(String.class);` and see if it returns null or not – harshithdwivedi Aug 23 '17 at 11:44
Still returns null :( – Simon Aug 23 '17 at 11:51
Check the updated answer and see if it fixes the issue, – harshithdwivedi Aug 23 '17 at 11:54
`String currentUser` doesn't show any value while debugging. – Simon Aug 23 '17 at 12:02
Ok, just check to see if the the user is authorized to access the db. – harshithdwivedi Aug 23 '17 at 12:07
In your screenshot you loop over the `dataSnapshot.getChildren()` in `onChildAdded()`. That's not needed, since `onChildAdded()` already is invoked on each user node. – Frank van Puffelen Aug 23 '17 at 12:17
sorry for the delay... @the-dagger, how to check if the user is authorized or not. – Simon Aug 23 '17 at 12:38

Firebase datasnapshot.getValue() returns null

1 Answers1