Invariant Violation: "main" has not been registered

Question

New to React Native: I started a brand new project with Expo init and then I followed the instructions mentioned inhttps://reactnavigation.org/docs/hello-react-navigation I run the project with expo start and I get this error. Invariant Violation: "main" has not been registered. This can happen if:

• Metro (the local dev server) is run from the wrong folder. Check if Metro is running, stop it and restart it in the current project.
• A module failed to load due to an error and AppRegistry.registerComponent wasn't called.

invariant browser.js:38:14 runApplication AppRegistry.js:193:13 __callFunction MessageQueue.js:425:19 __guard$argument_0 MessageQueue.js:112:6 __guard MessageQueue.js:373:10 callFunctionReturnFlushedQueue MessageQueue.js:111:4 callFunctionReturnFlushedQueue [native code]:0 Any suggestions?

Answer 1

Open the index.js, the content of the file should be like this:

import { AppRegistry, Platform } from 'react-native'; import App from './App';  AppRegistry.registerComponent('X', () => App);  if (Platform.OS === 'web') {     const rootTag = document.getElementById('root') || document.getElementById('X');     AppRegistry.runApplication('X', { rootTag }); } 

If you have this error Invariant Violation: “main” has not been registered you have to replace the 'X' by 'main'.

Another example :

If you have this error Invariant Violation: “app” has not been registered you have to replace the 'X' by 'app'.

For android :

Open ./android/app/src/main/java/[multiple folders]/MainActivity.java

/**    * Returns the name of the main component registered from JavaScript.    * This is used to schedule rendering of the component.    */   @Override   protected String getMainComponentName() {     return "X";   } 

The 'X' of MainActivity.java and index.js must match.