This is the error Android studio is showing me when i am pressing the button

Question

Logcat Output:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String firebase.firebasepractice.User.getUsername()' on a null object reference. ...

User:

MainActivity:

public class MainActivity extends AppCompatActivity {

  private EditText name,password;
  Button btn;
  TextView tv;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    name = (EditText) findViewById(R.id.userName);
    password= (EditText) findViewById(R.id.password);
    btn= (Button) findViewById(R.id.submit);
    tv= (TextView) findViewById(R.id.tv);

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            DatabaseReference myRef=FirebaseDatabase.getInstance().getReference("Users");

                String userId=myRef.push().getKey();

            myRef.child(userId).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    User user=dataSnapshot.getValue(User.class);
                    tv.setText("Name is "+user.getUsername()+"    Email is "+user.getEmail());
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
    });
}
}

Add snapshot detail and User model – Rahul Apr 02 '17 at 18:27 — Rahul, Apr 02 '17 at 18:27
I have added snapshot – Mahesh Chandra Apr 02 '17 at 19:17 — Mahesh Chandra, Apr 02 '17 at 19:17

score 0 · Answer 1 · answered Apr 02 '17 at 18:27

0

Because mapping between datasnapshot and User model is failed.

User user=dataSnapshot.getValue(User.class);
// check it null there
if(user != null) {
 tv.setText("Name is "+user.getUsername()+"    Email is "+user.getEmail());
}

answered Apr 02 '17 at 18:27

Rahul

10,457
4
35
55

the error message has gone but data is not retrieved from the firebase – Mahesh Chandra Apr 02 '17 at 19:01
@MaheshChandra Add datasnapshot of your Firebase and User java class in your question. – Rahul Apr 02 '17 at 19:02
added snapshot..please help – Mahesh Chandra Apr 02 '17 at 19:17

BhalchandraSW · Answer 2 · 2017-04-02T19:13:16.377

0

You are missing a no-args constructor in User class:

Please add:

public User() {
}

Then, you are initialising myRef like this:

myRef=FirebaseDatabase.getInstance().getReference("Users");

And then again accessing 'Users' node under 'Users'

myRef.child("Users")

Lastly, I believe you are passing a wrong variable to a .child() call in:

myRef.child("Users")
    .addValueEventListener ...

You should be doing:

myRef.child(userId) // this line is changed
    .addValueEventListener ...

Your final code should look like:

DatabaseReference myRef = FirebaseDatabase.getInstance().getReference("Users");

String userId = myRef.push().getKey();

myRef.child(userId) // Change: "Users" -> userId
    .addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            User user = dataSnapshot.getValue(User.class);
            tv.setText("Name is " + user.getUsername() + "\tEmail is " + user.getEmail());
        }

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

edited Apr 02 '17 at 19:13

answered Apr 02 '17 at 18:33

BhalchandraSW

714
5
13

I am still unable to fetch the result.. – Mahesh Chandra Apr 02 '17 at 19:02
@MaheshChandra Please check my edits. You are accessing 'Users' under 'Users' node – BhalchandraSW Apr 02 '17 at 19:09
tried this instead. Still nothing.. – Mahesh Chandra Apr 02 '17 at 19:12
Please add no-args constructor as per edits. – BhalchandraSW Apr 02 '17 at 19:20
please go through the snapshots. I have done edits but nothing worked – Mahesh Chandra Apr 02 '17 at 19:26
@MaheshChandra Maybe I am not seeing updated site. Did you add the no-argument constructor to User class? – BhalchandraSW Apr 02 '17 at 19:26
@MaheshChandra Please do not make changes to the meaning of the initial question. This makes the question different than the one you posted first and readers are left confused when they go through answers. Thank you. :) – BhalchandraSW Apr 02 '17 at 19:28

This is the error Android studio is showing me when i am pressing the button

2 Answers2