使用React Native Config for Android时缺失.env文件，请求协助排查

Hey there, let's tackle your two React Native issues one by one—they're both pretty common and straightforward to resolve!

Issue 1: "JS server already running" #

This error happens because the Metro bundler (React Native's JS server) is still running in the background, even if you thought you closed it. Here's how to fix it:

• Quick first step: If you have the Metro terminal window open, press Ctrl + C to terminate the process, then restart your app with npx react-native run-android.
• If the server lingers: Kill the Metro process manually:
  • On macOS/Linux: Run these commands in your terminal:

    lsof -i :8081  # Find the process ID (PID) using port 8081
    kill -9 <PID>  # Replace <PID> with the number from the previous command
    

  • On Windows: Open Task Manager, locate all node.exe processes linked to React Native/Metro, right-click and select "End Task".
• Reset cache and restart: You can also clear cached data and start fresh with this command:

  npx react-native start --reset-cache
  

Issue 2: "Missing .env file" #

Your build is trying to load environment variables from a .env file that doesn't exist in your project root. Here's what to do:

1. Create the .env file: Head to your project's root directory (not the android folder) and make a new file named .env.
2. Add your environment variables: Fill it with the variables your app needs, for example:

   API_BASE_URL=https://your-api-endpoint.com
   APP_DISPLAY_NAME=MyAwesomeApp
   

3. Verify your env setup: If you're using a library like react-native-dotenv, double-check your babel.config.js to ensure it's configured to read the .env file:

   module.exports = {
     presets: ['module:metro-react-native-babel-preset'],
     plugins: [
       ['module:react-native-dotenv', {
         moduleName: '@env',
         path: '.env',
         allowUndefined: false
       }]
     ]
   };
   

4. Rebuild the app: Go back to the android folder and run a clean build to make sure the new .env file is picked up:

   cd android && ./gradlew clean installDebug
   

After following these steps, both issues should be sorted out. Let me know if you hit any unexpected snags!

内容的提问来源于stack exchange，提问作者user1106888