Can't pass null for argument 'pathString' in child() in Firebase Database

Question

This is my fire base data structure:

I am retrieving the data from database using the following method

private DatabaseReference mFirebaseDatabase=FirebaseDatabase.getInstance().getReference();;
    private FirebaseDatabase mFirebaseInstance;

mFirebaseDatabase.child("users").child(userId).child(time).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                String value = dataSnapshot.getValue(String.class);
                Log.d("Tag", "Value is: " + value);
                System.out.println("Values is :::::::::::::::::::::::::::::::::::: "+value);


            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                // Failed to read value
                Log.w("Tag", "Failed to read value.", databaseError.toException());


            }
        });

i am getting the below error

 Caused by: java.lang.NullPointerException: Can't pass null for argument 'pathString' in child()

please help

userID part, this is where i create a new entry to store data to the table

 private void createUser(String name, String time, String lat, String lon) {
        // In real apps this userId should be fetched
        // by implementing firebase auth
        if (TextUtils.isEmpty(userId)) {
            userId = mFirebaseDatabase.push().getKey();
            System.out.println("Userid is ------------------------------> "+userId);
        }

        User user = new User(name, time,lat,lon);

        mFirebaseDatabase.child(userId).setValue(user);

        addUserChangeListener();
    }

    /**
     * User data change listener
     */
    private void addUserChangeListener() {
        // User data change listener
        mFirebaseDatabase.child(userId).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);

                // Check for null
                if (user == null) {
                    Log.e(TAG, "User data is null!");
                    return;
                }

                Log.e(TAG, "User data is changed!" + user.name + ", " + user.time);
                System.out.println("User data is changed!" + user.name + ", " + user.time);


            }

            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.e(TAG, "Failed to read user", error.toException());
            }
        });
    }

The above code is used for userId generation,userId is dynamically created every time when a insert function is called

Thats the reason its throwing null pointer exception..i think userId must have any value like "Ks7dk..." — Meenal, Aug 22 '17 at 09:18
but its made by the database do we need to save that or is there a way to get the userid..?@Meenal — , Aug 22 '17 at 09:25
@VishalRjm Can you please show the code where you are retrieving the `userId` ? — Catalin Ghita, Aug 22 '17 at 09:37
@VishalRjm Have you checked my answer? I think you are passing the path with the user's current `time` instead of simply passing the string "time" as a child — Catalin Ghita, Aug 22 '17 at 10:01

score 0 · Answer 1 · answered Aug 22 '17 at 09:22

0

make sure you're placing a value into either userId or child and that they're at least instantiated (should at least get rid of the nullpointerException)

answered Aug 22 '17 at 09:22

Alex Gold

105
8

score 0 · Answer 2 · answered Aug 22 '17 at 09:47

There is something wrong with the path you are assigning the ValueEventListener to.

Looking from your Firebase Database picture the only problem that could cause that NullPointerException is when you use .child(userId) or when you use .child(time)

How to fix your problem:

replace this .child(time) to .child("time")

make sure you are retrieving the userId this way:

private FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

...

protected void onCreate(Bundle savedInstanceState) {
...     
String userId = user.getUid();
...
}

Can't pass null for argument 'pathString' in child() in Firebase Database

2 Answers2

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