Fragment of code with Android MVP that checks login credentials via REST API

Question

I'm learning MVP for Android and am wondering if that piece of code that I wrote is correct in terms of this pattern or maybe is completely messed up.

I'm wondering if there can be return type other than void in contract interface like I have in Model interface, secondly context shouldn't be passed in constructor of presenter, then how should the model instance be created in presenter's constructor other way? This is my code:

public interface CredentialsContract {

interface Model {
    interface OnFinishedLoginListener {
        void onFinishedLogin(String body);
        void onFailureLogin(Throwable t);
    }
    void saveSomeCredentials(String nameLogin, String passLogin);
    void saveEmptyCredentials();
    String getNameCredential();
    String getPassCredential();
    boolean getCbCredential();
    void checkLogin(OnFinishedLoginListener onFinishedListener, String login, String pass);
}

interface View {
    void showBigProgressDialog();
    void hideBigProgressDialog();
    void setPropertiesWhenLoginIsTrue();
    void setPropertiesWhenLoginIsFalse();
    void setLoginTextViewText(String response);
    void setNameCredential(String name);
    void setPassCredential(String pass);
    void setCbCredential(boolean cbState);
}

interface Presenter {
    void saveSomeCredentials(String nameLogin, String passLogin);
    void saveEmptyCredentials();
    void checkLoginPresenter(String login, String pass);
    void setNameCredential();
    void setPassCredential();
    void setCbCredential();

   }
}

---

public class RestData implements CredentialsContract.Model {

private Context context;
private SharedPreferences pref;
private SharedPreferences.Editor editor;

public RestData(Context context) {
    this.context = context;
    pref = context.getSharedPreferences("Preferences", 0);
    editor = pref.edit();
}

@Override
public void saveSomeCredentials(String nameLogin, String passLogin) {
    editor.putString("userLogin", nameLogin); // Storing string
    editor.putString("userPassword", passLogin); // Storing string
    editor.putBoolean("cbSaveCredentials", true);
    editor.apply();
}

@Override
public void saveEmptyCredentials() {
    editor.putString("userLogin", ""); // Storing string
    editor.putString("userPassword", ""); // Storing string
    editor.putBoolean("cbSaveCredentials", false);
    editor.apply();
}

@Override
public void checkLogin(final OnFinishedLoginListener onFinishedListener, String login, String passWhenLogin) {
    Call<String> result = Api.getClient().checkLogin(login, passWhenLogin);
    result.enqueue(new Callback<String>() {
        @Override
        public void onResponse(Call<String> call, Response<String> response) {
                onFinishedListener.onFinished(response.body());      
        }

        @Override
        public void onFailure(Call<String> call, Throwable t) {
            Log.e("tag", t.toString());
            onFinishedListener.onFailure(t);
        }
    });
    }

@Override
public String getNameCredential() {
    return pref.getString("userLogin", "");
}

@Override
public String getPassCredential() {
    return pref.getString("userPassword", "");
}

@Override
public boolean getCbCredential() {
    return pref.getBoolean("cbSaveCredentials", false);
}
}

---

public class Credentials extends AppCompatActivity implements CredentialsContract.View {

private EditText etNameLogin, etPassLogin;
private CheckBox cbSaveCredentials, cbTerms;
private TextView tvLoginStatus, tvRegistrationStatus;
private ProgressBar pbBig;
private CredentialsPresenter credentialsPresenter;
private Button bOk;

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

    credentialsPresenter = new CredentialsPresenter(this, this);

    initUIFields(pref);

    credentialsPresenter.setNameCredential();
    credentialsPresenter.setPassCredential();
    credentialsPresenter.setCbCredential();

    findViewById(R.id.tvTerms).setOnClickListener(v -> initRegulationsDialog());

    bOk = findViewById(R.id.bOk);
    bOk.setOnClickListener(v -> {
        if (cbSaveCredentials.isChecked())
            credentialsPresenter.saveSomeCredentials(etNameLogin.getText().toString(), etPassLogin.getText().toString());
        else
            credentialsPresenter.saveEmptyCredentials();

        Intent i = new Intent(getApplicationContext(), Gra.class);
        i.putExtra("userLogin", etNameLogin.getText().toString());
        i.putExtra("onlineGame", true);
        startActivity(i);
    });

    findViewById(R.id.bLogin).setOnClickListener(v -> credentialsPresenter.checkLoginPresenter(etNameLogin.getText().toString(), etPassLogin.getText().toString()));

}

public void initUIFields(SharedPreferences pref) {
    etNameLogin = findViewById(R.id.etNameLogin);
    etPassLogin = findViewById(R.id.etPassLogin);
    cbSaveCredentials = findViewById(R.id.cbSaveCredentials);
    etNameRegistration = findViewById(R.id.etName);
    etEmailRegistration = findViewById(R.id.etEmailRegistration);
    etPassRegistration = findViewById(R.id.etPassRegistration);
    etPassConfirmationRegistration = findViewById(R.id.etPassConfirmationRegistration);
    cbTerms = findViewById(R.id.cbTerms);
    tvLoginStatus = findViewById(R.id.tvLoginStatus);
    tvRegistrationStatus = findViewById(R.id.tvRegistrationStatus);
    pbBig = findViewById(R.id.bigProgressBar);
}

public void initRegulationsDialog() {
    AlertDialog.Builder dialogRegulations = new AlertDialog.Builder(Credentials.this);
    dialogRegulations.setTitle("Terms and conditions");
    dialogRegulations.setMessage("Content");
    dialogRegulations.setCancelable(false);
    dialogRegulations.setNeutralButton("OK", (dialog1, which) -> dialog1.dismiss());
    dialogRegulations.show();
}

@Override
public void showBigProgressDialog() {
    pbBig.setVisibility(View.VISIBLE);
}

@Override
public void hideBigProgressDialog() {
    pbBig.setVisibility(View.INVISIBLE);
}

@Override
public void setPropertiesWhenLoginIsTrue() {
    bOk.setEnabled(true);
    tvLoginStatus.setTextColor(ContextCompat.getColor(this, R.color.green));
}

@Override
public void setPropertiesWhenLoginIsFalse() {
    bOk.setEnabled(false);
    tvLoginStatus.setTextColor(ContextCompat.getColor(this, R.color.red));
}

@Override
public void setLoginTextViewText(String response) {
    tvLoginStatus.setText(response);
    }

@Override
public void setNameCredential(String name) {
    etNameLogin.setText(name);
}

@Override
public void setPassCredential(String pass) {
    etPassLogin.setText(pass);
}

@Override
public void setCbCredential(boolean cbState) {
    cbSaveCredentials.setChecked(cbState);
}
}

---

public class CredentialsPresenter implements CredentialsContract.Presenter, CredentialsContract.Model.OnFinishedLoginListener {

CredentialsContract.Model model;
CredentialsContract.View view;
SharedPreferences sharedPreferences;
SharedPreferences.Editor editor;

public CredentialsPresenter(Context context, CredentialsContract.View view) {
    model = new RestData(context);
    this.view = view;
    this.sharedPreferences = sharedPreferences;
    editor = sharedPreferences.edit();
}

@Override
public void saveSomeCredentials(String nameLogin, String passLogin) {
    editor.putString("userLogin", nameLogin);
    editor.putString("userPassword", passLogin);
    editor.putBoolean("cbSaveCredentials", true);
    editor.apply();
}

@Override
public void saveEmptyCredentials() {
    editor.putString("userLogin", "");
    editor.putString("userPassword", "");
    editor.putBoolean("cbSaveCredentials", false);
    editor.apply();
}

@Override
public void checkLoginPresenter(String login, String passWhenLogin) {
    view.showBigProgressDialog();
    model.checkLogin(this, login, passWhenLogin);
}

@Override
public void onFinishedLogin(String body) {
    view.setLoginTextViewText(body);
    if(body.contains("true"))
        view.setPropertiesWhenLoginIsTrue();
    if(body.contains("false"))
        view.setPropertiesWhenLoginIsFalse();
    view.hideBigProgressDialog();
}

@Override
public void onFailureLogin(Throwable t) {
    view.hideBigProgressDialog();
    }

@Override
public void setNameCredential() {
    view.setNameCredential(model.getNameCredential());
}

@Override
public void setPassCredential() {
    view.setPassCredential(model.getPassCredential());
}

@Override
public void setCbCredential() {
    view.setCbCredential(model.getCbCredential());
}
}