Login MVP

activity_login.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="250dp"
              android:layout_height="wrap_content"
              android:layout_gravity="center_horizontal"
              android:gravity="center"
              android:orientation="vertical"
              android:layout_marginTop="16dp"
    >

    <EditText
        android:id="@+id/username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_vertical"
        android:hint="@string/user_name"
        android:drawableLeft="@drawable/ic_action_person"
        android:drawablePadding="8dp"
        />
    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_vertical"
        android:hint="@string/password"
        android:inputType="textPassword"
        android:drawableLeft="@drawable/ic_action_accounts"
        android:drawablePadding="8dp"
        />
    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/log_in"
        android:drawableRight="@drawable/ic_action_accept"
        />
    <ProgressBar
        android:id="@+id/progress"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:visibility="gone"
        />

</LinearLayout>

LoginActivity.java

public class LoginActivity extends Activity implements LoginView, View.OnClickListener {

    private ProgressBar progressBar;
    private EditText username;
    private EditText password;
    private LoginPresenter presenter;

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

        progressBar = (ProgressBar) findViewById(R.id.progress);
        username = (EditText) findViewById(R.id.username);
        password = (EditText) findViewById(R.id.password);
        findViewById(R.id.button).setOnClickListener(this);

        presenter = new LoginPresenterImpl(this);
    }

    @Override public void showProgress() {
        progressBar.setVisibility(View.VISIBLE);
    }

    @Override public void hideProgress() {
        progressBar.setVisibility(View.GONE);
    }

    @Override public void setUsernameError() {
        username.setError(getString(R.string.username_error));
    }

    @Override public void setPasswordError() {
        password.setError(getString(R.string.password_error));
    }

    @Override public void navigateToHome() {
        startActivity(new Intent(this, MainActivity.class));
        finish();
    }

    @Override public void onClick(View v) {
        presenter.validateCredentials(username.getText().toString(), password.getText().toString());
    }
}

LoginInteractor.java

public interface LoginInteractor {
    public void login(String username, String password, OnLoginFinishedListener listener);
}

LoginInteractorImpl.java

public class LoginInteractorImpl implements LoginInteractor {

    @Override
    public void login(final String username, final String password, final OnLoginFinishedListener listener) {

        // Mock login. I'm creating a handler to delay the answer a couple of seconds
        new Handler().postDelayed(new Runnable() {
            @Override public void run() {
                boolean error = false;
                if (TextUtils.isEmpty(username)){
                    listener.onUsernameError();
                    error = true;
                }
                if (TextUtils.isEmpty(password)){
                    listener.onPasswordError();
                    error = true;
                }
                if (!error){
                    listener.onSuccess();
                }
            }
        }, 2000);
    }
}

LoginPresenter.java

public interface LoginPresenter {
    public void validateCredentials(String username, String password);
}

LoginPresenterImpl.java

public class LoginPresenterImpl implements LoginPresenter, OnLoginFinishedListener {

    private LoginView loginView;
    private LoginInteractor loginInteractor;

    public LoginPresenterImpl(LoginView loginView) {
        this.loginView = loginView;
        this.loginInteractor = new LoginInteractorImpl();
    }

    @Override public void validateCredentials(String username, String password) {
        loginView.showProgress();
        loginInteractor.login(username, password, this);
    }

    @Override public void onUsernameError() {
        loginView.setUsernameError();
        loginView.hideProgress();
    }

    @Override public void onPasswordError() {
        loginView.setPasswordError();
        loginView.hideProgress();
    }

    @Override public void onSuccess() {
        loginView.navigateToHome();
    }
}

LoginView.java

public interface LoginView {
    public void showProgress();

    public void hideProgress();

    public void setUsernameError();

    public void setPasswordError();

    public void navigateToHome();
}

OnLoginFinishedListener.java

public interface OnLoginFinishedListener {

    public void onUsernameError();

    public void onPasswordError();

    public void onSuccess();
}