React-Native, BleManager "Native Module cannot be null" - react-native

Question

I wanted to try out the react-native-ble-plx library from Polidea
https://github.com/Polidea/react-native-ble-plx
So I created a new app in terminal and installed the library as explained by Polidea
create-react-native-app playground
npm install --save react-native-ble-plx
react-native link react-native-ble-plx
I then ran npm start and then i (for opening in iOS simulator)
and then I got the following error (in the terminal and in the simulator)
Native module cannot be null
node_modules/react-native/node_modules/fbjs/lib/invariant.js:44:24 in invariant
node_modules/react-native/Libraries/EventEmitter/NativeEventEmitter.js:31:16 in NativeEventEmitter
node_modules/react-native-ble-plx/src/BleManager.js:52:25 in BleManager
App.js:8:19 in App
node_modules/react-native/Libraries/Renderer/ReactNativeStack-dev.js:1679:33 in
node_modules/react-native/Libraries/Renderer/ReactNativeStack-dev.js:1610:15 in measureLifeCyclePerf
... 52 more stack frames from framework internals
Here is the code in App.js:
import React from 'react';
import { StyleSheet, Text, View } from 'react-native';
import {BleManager} from 'react-native-ble-plx';
//importing BleManager without calling new BleManager() works
export default class App extends React.Component {
constructor(){
super();
this.manager = new BleManager();
}
//calling new BleManager() leads to error
render() {
return (
<View style={styles.container}>
<Text>nothing, just sucking errors</Text>
</View>
);
}
}
const styles = StyleSheet.create({
container: {
flex: 1,
backgroundColor: '#fff',
alignItems: 'center',
justifyContent: 'center',
},
});
Here is the file package.json
{
"name": "playground",
"version": "0.1.0",
"private": true,
"devDependencies": {
"react-native-scripts": "1.5.0",
"jest-expo": "^21.0.2",
"react-test-renderer": "16.0.0-alpha.12"
},
"main": "./node_modules/react-native-scripts/build/bin/crna-entry.js",
"scripts": {
"start": "react-native-scripts start",
"eject": "react-native-scripts eject",
"android": "react-native-scripts android",
"ios": "react-native-scripts ios",
"test": "node node_modules/jest/bin/jest.js --watch"
},
"jest": {
"preset": "jest-expo"
},
"dependencies": {
"expo": "^21.0.0",
"react": "16.0.0-alpha.12",
"react-native": "^0.48.4",
"react-native-ble-plx": "^0.6.3"
}
}
I already looked for help and tried
npm -rm rf node_modules
npm install
but it didn't help.
Here is my system information:
macOS High Sierra
iMac (27-inch, Mid 2010)
Processor 2.8 GHz Intel Core i5
Memory 16 GB 1333 MHz DDR3
I also got the same error when opening the app in my iPhone(6s, 10.3.1) (after scanning QR code in terminal from npm start)
Other apps without the react-native-ble-plx library work normally.
Looking forward receiving some help.
Thanks in advance.
Frank

Answer 1

You have used create-react-native-app to create your React Native project. So you can not use react-native-ble-plx library with this project. Because to access Bluetooth hardware, react-native-ble-plx package has some native code written in android and ios seperately.
If you want to build your app, you'll need to eject from create-react-native-app and use Xcode and Android Studio.
Use the below command:--
npm install -g react-native-cli
npm run eject
react-native link react-native-ble-plx
1st command is to install react-native-cli globally
2nd command is to convert your project from Expo project to regular React Native project
3rd command is to link react-native-ble-plx. Because most probably your previous link was failed.

Answer 2

What I did was (after completely removing ble-plx by discarding git changes before I started)
navigating to /node_modules/react-native-ble-plx/ios/BleClient.xcodeproj and
I pulled that into the Libraries folder in the project navigator
Then I went to my target -> build phases -> link binary with libraries and added libBleClient.a