Using Google FireBase to create a simple chat on Android

• The main screen for selecting an input parameter (Login or Registration) and displaying the number of registered users
• Login for user authentication
• The registration screen in which we create a new Users - Chat screen (which can display a chat fragment or a ListOfUsers fragment)

Main screen

MainActivityPresenter :

  public class MainActivityPresenterImpl implements MainPresenter {
    private final MainView mainView;
    private final MainInteractor interactor;
    public MainActivityPresenterImpl(MainView view) {
        this.mainView = view;
        interactor = new MainInteractor(this);
    }
    @Override
    public void receiveRequest() {
        interactor.receiveRequest();
    }
    @Override
    public String getNumberOfUsers(long numberOfUsers) {
        return "Online users: " + String.valueOf(numberOfUsers);
    }
    @Override
    public void sendNumberOfChildren(long number) {
        mainView.setNumberOfUsersTextView(getNumberOfUsers(number));
    }
} 

  public class MainInteractor implements MInteractor {
    private final Firebase mainRef = new Firebase("https:///currentUsers");
    private final MainPresenter presenter;
    public MainInteractor(MainPresenter pre) {
        this.presenter = pre;
    }
    @Override
    public void receiveRequest() {
        mainRef.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                presenter.sendNumberOfChildren(dataSnapshot.getChildrenCount());
            });
    }
}

Registration screen

public class FirebaseUserRegisterPresenterImpl implements FirebaseUserRegisterPresenter {
    private final RegisterView registerView;
    private final RegisterInteractor interactor;
    public FirebaseUserRegisterPresenterImpl(RegisterView view) {
        this.registerView = view;
        this.interactor = new RegisterInteractor(this);
    }
    @Override
    public void receiveRegisterRequest(String username, String email, String password, String emoji) {
        interactor.receiveRegisterRequest(username, email, password, emoji);
        registerView.spinProgressBar();
    }
    @Override
    public void onFailure() {
        registerView.onFailure();
        registerView.stopProgressBar();
    }
    @Override
    public void onSuccess() {
        registerView.onSuccess();
        registerView.stopProgressBar();
    }
}

Interactor:

   public class RegisterInteractor implements RInteractor {
    private Firebase userRef = new Firebase("https:///Users/");
    private final FirebaseUserRegisterPresenter presenter;
    public RegisterInteractor(FirebaseUserRegisterPresenter pre) {
        this.presenter = pre;
    }
    @Override
    public void receiveRegisterRequest(final String username, String email, String password, final String emoji) {
        userRef.createUser(email, password, new Firebase.ValueResultHandler>() {
            @Override
            public void onSuccess(Map stringObjectMap) {
                String uid = stringObjectMap.get("uid").toString();
                userRef = new Firebase("https:///Users/" + uid);
                userRef.setValue(createUser(username, emoji));
                presenter.onSuccess();
            }
            @Override
            public void onError(FirebaseError firebaseError) {
                presenter.onFailure();
            }
        });
    }
    @Override
    public Map createUser(String username, String emoji) {
        Map user = new HashMap<>();
        user.put("username", username);
        user.put("emoji", emoji);
        return user;
    }
}

Login screen

What happens when a user clicks Login?

public class FirebaseLoginPresenterImpl implements FirebaseLoginPresenter {
    private final LoginView loginView;
    private final LoginInteractor interactor;
    public FirebaseLoginPresenterImpl(LoginView view) {
        this.loginView = view;
        interactor = new LoginInteractor(this);
    }
    @Override
    public void receiveUserLogin(String email, String password) {
        loginView.spinProgressBar();
        interactor.attemptToLogIn(email, password);
    }
    @Override
    public void onFailure() {
        loginView.stopProgressBar();
        loginView.onFailure();
    }
    @Override
    public void onSuccess(String user, String uid) {
        loginView.stopProgressBar();
        loginView.logTheUserIn(user, uid);
    }
}

• A successful login sends the username of the user, and the UID sends the intention in which the ChatActivity login starts - Failed warns the user with Toast.

Chat screen

Adapter

public class CustomMessageRecyclerAdapter extends RecyclerView.Adapter implements MessageAdapterView {
    private final ArrayList mMessageList = new ArrayList<>();
    private final String user;
    private final MessagePresenterImpl presenter;
    public CustomMessageRecyclerAdapter(String username) {
        this.user = username;
        presenter = new MessagePresenterImpl(this);
    }
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.chat_message, parent, false);
        return new ViewHolder(v);
    }
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        Message current = mMessageList.get(position);
        if (current.getAuthor().equals(user)) {
            holder.mAuthorTextView.setText("You");
        } else {
            holder.mAuthorTextView.setText(current.getAuthor());
        }
        holder.mMessageTextView.setText(current.getMessage());
        holder.mEmojiTextView.setText(current.getEmoji());
    }
    @Override
    public int getItemCount() {
        return mMessageList.size();
    }
    @Override
    public void addItem(Message message) {
        mMessageList.add(message);
        notifyDataSetChanged();
    }
    @Override
    public void request() {
        presenter.requestMessages();
    }
    public class ViewHolder extends RecyclerView.ViewHolder {
        private TextView mAuthorTextView;
        private TextView mMessageTextView;
        private TextView mEmojiTextView;
        public ViewHolder(View itemView) {
            super(itemView);
            mAuthorTextView = (TextView) itemView.findViewById(R.id.message_author);
            mMessageTextView = (TextView) itemView.findViewById(R.id.message_value);
            mEmojiTextView = (TextView) itemView.findViewById(R.id.message_emoji);
        }
    }
}

Presenter:

public class MessagePresenterImpl implements MessagePresenter {
    private final MessageAdapterView adapterView;
    private final MessageInteractor interactor;
    public MessagePresenterImpl(MessageAdapterView view) {
        this.adapterView = view;
        this.interactor = new MessageInteractor(this);
    }
    @Override
    public void sendMessageToAdapter(Message message) {
        adapterView.addItem(message);
    }
    @Override
    public void requestMessages() {
        interactor.request();
    }
}

Interactor :

public class MessageInteractor {
    private final MessagePresenter presenter;
    private final Firebase mMessagesRef = new Firebase("https:///messages");
    private final Query mMessageQuery;
    public MessageInteractor(MessagePresenter pre) {
        this.presenter = pre;
        this.mMessageQuery = mMessagesRef.orderByValue().limitToLast(100);
    }
    public void request() {
        mMessageQuery.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                presenter.sendMessageToAdapter(dataSnapshot.getValue(Message.class));
            }
//some more auto-generated methods

public class ChatLoginInteractor implements CLoginInteractor {
    @Override
    public void logTheUserOut(String uid) {
        Firebase userRef = new Firebase("https:///currentUsers/" + uid);
        userRef.removeValue(); //removes the Child from Firebase
    }
}

How it works, step by step .

• Firebase uses Jackson parsing, so your POJOs need empty constructors, and setters need generation
• you really don't need special REST clients, since the DataSnapshot function can do all the parsing of the data using .getValue (POJO.class)
• In real time ... All requests and clicks on Firebase are extremely fast, since all data is formatted as JSON objects.

Conclusion :