Working example of Android MVP

As we already know about MVP that why and how to use MVP architecture, today will see a working example.

Firstly will write a Interface which will interact with activity and presenter.

public interface LoginActivityMVP {
    interface View {
        String getFirstName();
        String getLastName();
        void showUserNotAvailable();
        void showInputError();
        void showUserSavedMessage();
        void setFirstName(String firstName);
        void setLastName(String lastName);
    }

    interface Presenter {
        void setView(LoginActivityMVP.View view);
        void loginButtonClicked();
        void getCurrentUser();
    }

    interface Model {
        void createUser(String firstName, String lastName);
        User getUser();
    }
}

now will create a presenter which will interact with activity for particular event

public class LoginActivityPresenter implements LoginActivityMVP.Presenter {

    @Nullable
    private LoginActivityMVP.View view;
    private LoginActivityMVP.Model model;

    LoginActivityPresenter(LoginActivityMVP.Model model) {
        this.model = model;
    }

    @Override
    public void setView(LoginActivityMVP.View view) {
        this.view = view;
    }

    @Override
    public void loginButtonClicked() {
        if (view != null) {
            if (TextUtils.isEmpty(view.getFirstName()) || TextUtils.isEmpty(view.getLastName())) {
                view.showInputError();
            } else {
                model.createUser(view.getFirstName(), view.getLastName());
                view.showUserSavedMessage();
            }
        }
    }

    @Override
    public void getCurrentUser() {
        User user = model.getUser();
        if (user == null) {
            if (view != null) {
                view.showUserNotAvailable();
            }
        } else {
            if (view != null) {
                view.setFirstName(user.getFirstName());
                view.setLastName(user.getLastName());
            }
        }
    }
}

Now will create a activity which will initialise the presenter and presenter contains all business logic

public class LoginActivity extends AppCompatActivity implements LoginActivityMVP.View {

    LoginActivityMVP.Presenter presenter;

    private EditText firstName, lastName;
    private Button loginButton;

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

        presenter = new LoginActivityPresenter(<create a class and implement model interface which will handle create user logic>);

        firstName = findViewById(R.id.loginActivity_firstName_editText);
        lastName = findViewById(R.id.loginActivity_lastName_editText);
        loginButton = findViewById(R.id.loginActivity_login_button);

        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });
    }

    @Override
    protected void onResume() {
        super.onResume();
        presenter.setView(this);
    }

    @Override
    public String getFirstName() {
        return firstName.getText().toString();
    }

    @Override
    public String getLastName() {
        return lastName.getText().toString();
    }

    @Override
    public void showUserNotAvailable() {
        Toast.makeText(this, "User is not available", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void showInputError() {
        Toast.makeText(this, "cannot be empty", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void showUserSavedMessage() {
        Toast.makeText(this, "User saved", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void setFirstName(String firstName) {
        this.firstName.setText(firstName);
    }

    @Override
    public void setLastName(String lastName) {
        this.lastName.setText(lastName);
    }
}

and here is our user Model

public class User {
    private int id;
    private String firstName, lastName;

    public User(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

we have to create a model which will extends Model and will handle createUser logic.

Thanks for reading, please let me know if you have any doubts.