MainActivity.java

public class MainActivity extends AppCompatActivity {

    public static String TAG = "FirebaseUI.chat";
    private Firebase mRef;
    private Query mChatRef;
    private long userId = 2;
    private String mName = "Upin";
    private String mTime;
    private Button mSendButton;
    private EditText mMessageEdit;

    private RecyclerView mMessages;
    private FirebaseRecyclerAdapter<ChatModel, ChatHolder> mRecycleViewAdapter;

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

        mSendButton = (Button) findViewById(R.id.sendButton);
        mMessageEdit = (EditText) findViewById(R.id.messageEdit);

        mSendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                showFirebaseLoginPrompt();
            }
        });



        mRef = new Firebase("https://wirasetiawan29.firebaseio.com/chat");
        mChatRef = mRef.limitToLast(50);

        mSendButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ChatModel chat = new ChatModel(mMessageEdit.getText().toString(), mName, userId, System.currentTimeMillis(), mTime);
                mRef.push().setValue(chat, new Firebase.CompletionListener() {
                    @Override
                    public void onComplete(FirebaseError firebaseError, Firebase firebase) {
                        if (firebaseError != null) {
                            Log.e(TAG, firebaseError.toString());
                        }
                    }
                });
                mMessageEdit.setText("");
            }
        });

        mMessages = (RecyclerView) findViewById(R.id.messagesList);

        LinearLayoutManager manager = new LinearLayoutManager(this);
        manager.setReverseLayout(false);

        mMessages.setHasFixedSize(false);
        mMessages.setLayoutManager(manager);

        mRecycleViewAdapter = new FirebaseRecyclerAdapter<ChatModel, ChatHolder>(ChatModel.class, R.layout.text_message, ChatHolder.class, mChatRef) {
            @Override
            public void populateViewHolder(ChatHolder chatView, ChatModel chat, int position) {
                chatView.setText(chat.getMessage());
                chatView.setName(chat.getName());
                chatView.setTime(chat.getFormattedTime());


                if (chat.getUserId() == 2) {
                    chatView.setIsSender(true);
                } else {
                    chatView.setIsSender(false);
                }
            }
        };

        mMessages.setAdapter(mRecycleViewAdapter);
    }

    public static class ChatHolder extends RecyclerView.ViewHolder {
        View mView;

        public ChatHolder(View itemView) {
            super(itemView);
            mView = itemView;
        }

        public void setIsSender(Boolean isSender) {
            FrameLayout left_arrow = (FrameLayout) mView.findViewById(R.id.left_arrow);
            FrameLayout right_arrow = (FrameLayout) mView.findViewById(R.id.right_arrow);
            RelativeLayout messageContainer = (RelativeLayout) mView.findViewById(R.id.message_container);
            LinearLayout message = (LinearLayout) mView.findViewById(R.id.message);


            if (isSender) {
                left_arrow.setVisibility(View.GONE);
                right_arrow.setVisibility(View.VISIBLE);
                messageContainer.setGravity(Gravity.RIGHT);
            } else {
                left_arrow.setVisibility(View.VISIBLE);
                right_arrow.setVisibility(View.GONE);
                messageContainer.setGravity(Gravity.LEFT);
            }
        }

        public void setName(String name) {
            TextView field = (TextView) mView.findViewById(R.id.name_text);
            field.setText(name);
        }

        public void setText(String text) {
            TextView field = (TextView) mView.findViewById(R.id.message_text);
            field.setText(text);
        }

        public void setTime(String time){
            TextView field = (TextView) mView.findViewById(R.id.time_text);
            field.setText(time);
        }
    }

}