package com.reactdemo;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.KeyEvent;import com.facebook.react.LifecycleState;import com.facebook.react.ReactInstanceManager;import com.facebook.react.ReactRootView;import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;import com.facebook.react.shell.MainReactPackage;public class MainActivity extends AppCompatActivity implements DefaultHardwareBackBtnHandler { private ReactInstanceManager mReactInstanceManager; private ReactRootView mReactRootView; @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  mReactRootView = new ReactRootView(this);  mReactInstanceManager = ReactInstanceManager.builder()    .setApplication(getApplication())    .setBundleAssetName("index.android.bundle")    .setJSMainModuleName("index.android")    .addPackage(new MainReactPackage())    .setUseDeveloperSupport(BuildConfig.DEBUG)    .setInitialLifecycleState(LifecycleState.RESUMED)    .build();  mReactRootView.startReactApplication(mReactInstanceManager, "ReactDemo", null);  setContentView(mReactRootView); } @Override public boolean onKeyUp(int keyCode, KeyEvent event) {  if (keyCode == KeyEvent.KEYCODE_MENU && mReactInstanceManager != null) {   mReactInstanceManager.showDevOptionsDialog();   return true;  }  return super.onKeyUp(keyCode, event); } @Override public void onBackPressed() {  if (mReactInstanceManager != null) {   mReactInstanceManager.onBackPressed();  } else {   super.onBackPressed();  } } @Override public void invokeDefaultOnBackPressed() {  super.onBackPressed(); } @Override protected void onPause() {  super.onPause();  if (mReactInstanceManager != null) {   mReactInstanceManager.onHostPause();  } } @Override protected void onResume() {  super.onResume();  if (mReactInstanceManager != null) {   mReactInstanceManager.onHostResume(this, this);  } }}