react-native-nfc-manager Warning: TypeError - Cannot convert null value to object in React Native Expo

Question

I'm encountering an issue with react-native-nfc-manager in a React Native Expo project, where I'm receiving the following warning: TypeError: Cannot convert null value to object

I'm using react-native-nfc-manager for NFC functionalities in my React Native Expo project. The warning occurs in a specific scenario, and I'm unsure about the cause or how to resolve it.

import { StatusBar } from 'expo-status-bar';
import { StyleSheet, Text, View } from 'react-native';
import NfcManager, {Ndef, NfcTech, ByteParser} from 'react-native-nfc-manager';
export default function App() {

  NfcManager.isSupported(NfcTech.MifareClassic)
    .then(() => console.log('Mifare is supported'))
    .catch(err => console.warn(err))

  return (
    <View style={styles.container}>
      <Text>Open up App.js to start working on your app!</Text>
      <StatusBar style="auto" />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});

I am expecting that it returns Mifare is supported or not in the console. But it's rather returning Cannot convert null value to object

Answer 1

The error suggests that the native part is not configured correctly, which causes the NfcManager to be evaluated to null.

First of all, be aware that react-native-nfc-manager does not work with Expo Go, since it needs custom native code.

I assume that you are not using Expo Go. In this case, check that you have added the config plugin to the plugins array of your app.json or app.config.js

{
  "expo": {
    "plugins": ["react-native-nfc-manager"]
  }
}

Next, you need to rebuild your project as described in the expo documentation.