react-native-android-env

android {
    defaultConfig {
      buildConfigField "String",  "API_URL",     '"https://myapi.com"'
      buildConfigField "Boolean", "SHOW_ERRORS", "true"
      ...

var Config = require('react-native-android-config');
 
Config.API_URL     // "https://myapi.com" 
Config.SHOW_ERRORS // true 

API_URL="https://:secret@myapi.com"

defaultConfig {
    def props = new Properties()
    props.load(new FileInputStream(rootProject.file('config.properties')))
    props.each { key, val -> buildConfigField "String", key, val }
}

include ':react-native-android-config'
include ':app'
 
project(':react-native-android-config').projectDir = new File(rootProject.projectDir,
  '../node_modules/react-native-android-config/android')

dependencies {
    ...
    compile project(':react-native-android-config')
}

import com.lugg.ReactConfig.ReactConfigPackage; // add import 
 
public class MainActivity extends Activity implements DefaultHardwareBackBtnHandler {
 
    private ReactInstanceManager mReactInstanceManager;
    private ReactRootView mReactRootView;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mReactRootView = new ReactRootView(this);
 
        // initialize our PhotoRequest handler 
        mPhotoRequest = new ReactPhotoRequestPackage(this);
 
        mReactInstanceManager = ReactInstanceManager.builder()
                .setApplication(getApplication())
                .setBundleAssetName("index.android.bundle")
                .setJSMainModuleName("index.android")
                .addPackage(new MainReactPackage())
                .addPackage(new ReactConfigPackage()) // add the package here