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());
}
}