public class MyReactActivity extends Activity implements DefaultHardwareBackBtnHandler {
private ReactRootView mReactRootView;
private ReactInstanceManager mReactInstanceManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mReactRootView = new ReactRootView(this);
    mReactInstanceManager = ReactInstanceManager.builder()
            .setApplication(getApplication())
            .setCurrentActivity(this)
            .setBundleAssetName("index.android.bundle")
            .setJSMainModulePath("index")
            .addPackage(new MainReactPackage())
            .setUseDeveloperSupport(BuildConfig.DEBUG)
            .setInitialLifecycleState(LifecycleState.RESUMED)
            .build();
    // The string here (e.g. "MyReactNativeApp") has to match
    // the string in AppRegistry.registerComponent() in index.js
    mReactRootView.startReactApplication(mReactInstanceManager, "MyReactNativeApp", null);

    setContentView(mReactRootView);
}

@Override
public void invokeDefaultOnBackPressed() {
    super.onBackPressed();
}
}