Android App can't write data to Firebase database

Question

I'm trying to follow a tutorial from Udacity to build a chat app with Firebase. Though I followed every instructions, I'm having trouble to write data to the firebase realtime database on button press.

App is running perfectly on the simulator. But whenever I hit the send button, no data shows up in the database. Check the screenshot of the app.

App Screenshot

Added the google services json file.
Added all the dependencies that needed and applied google services plugin in the Build.gradle (app) file.
Added google services classpath in the Build.grade (project) file.
Changed the firebase security rules to the test mode.

What am I doing wrong? Please help.

MainActivity.java file looks like this:

package com.google.firebase.udacity.friendlychat;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.Editable;
import android.text.InputFilter;
import android.text.TextWatcher;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;
import android.widget.ProgressBar;

import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.DatabaseReference;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    public static final String ANONYMOUS = "anonymous";
    public static final int DEFAULT_MSG_LENGTH_LIMIT = 1000;

    private ListView mMessageListView;
    private MessageAdapter mMessageAdapter;
    private ProgressBar mProgressBar;
    private ImageButton mPhotoPickerButton;
    private EditText mMessageEditText;
    private Button mSendButton;

    private String mUsername;

    private FirebaseDatabase mFirebaseDatabase;
    private DatabaseReference mMessagesDatabaseReference;

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

        mUsername = ANONYMOUS;

        mFirebaseDatabase = FirebaseDatabase.getInstance();
        mMessagesDatabaseReference = mFirebaseDatabase.getReference().child("messages");

        // Initialize references to views
        mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
        mMessageListView = (ListView) findViewById(R.id.messageListView);
        mPhotoPickerButton = (ImageButton) findViewById(R.id.photoPickerButton);
        mMessageEditText = (EditText) findViewById(R.id.messageEditText);
        mSendButton = (Button) findViewById(R.id.sendButton);

        // Initialize message ListView and its adapter
        List<FriendlyMessage> friendlyMessages = new ArrayList<>();
        mMessageAdapter = new MessageAdapter(this, R.layout.item_message, friendlyMessages);
        mMessageListView.setAdapter(mMessageAdapter);

        // Initialize progress bar
        mProgressBar.setVisibility(ProgressBar.INVISIBLE);

        // ImagePickerButton shows an image picker to upload a image for a message
        mPhotoPickerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // TODO: Fire an intent to show an image picker
            }
        });

        // Enable Send button when there's text to send
        mMessageEditText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
                if (charSequence.toString().trim().length() > 0) {
                    mSendButton.setEnabled(true);
                } else {
                    mSendButton.setEnabled(false);
                }
            }

            @Override
            public void afterTextChanged(Editable editable) {
            }
        });
        mMessageEditText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(DEFAULT_MSG_LENGTH_LIMIT)});

        // Send button sends a message and clears the EditText
        mSendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FriendlyMessage friendlyMessage = new FriendlyMessage(mMessageEditText.getText().toString(), mUsername, null);
                // Clear input box
                mMessageEditText.setText("");
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        return super.onOptionsItemSelected(item);
    }
}

Answer 1

Nothing goes into your database because you aren't writing something in it at all. You are creating an object of FriendlyMessage class but you aren't doing something with it. To solve this, write that object to Firebase database using the following lines of code:

mMessagesDatabaseReference.push().setValue(friendlyMessage);

You should place this line of code, right after the declaration of your friendlyMessage object.

Answer 2

    // Send button sends a message and clears the EditText
    mSendButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            FriendlyMessage friendlyMessage = new FriendlyMessage(mMessageEditText.getText().toString(), mUsername, null);
            // here you have to write code for save to firebase DB
            mMessagesDatabaseReference.push().setValue(friendlyMessage);
            // Clear input box
            mMessageEditText.setText("");
        }
    });

after that you have to read data from firebase and add it to your list.