React Native Bluetooth on Android (Nano X only) | Developers

React Native Bluetooth on Android (Nano X only)

Estimated reading time: More than 10 minutes

Introduction

In this section you will see how to create a React Native application using the @ledgerhq/react-native-hw-transport-ble. For this project some general prerequisites are mandatory and you can find them here.

Then you can now go through the prerequisite for Android development below.

Prerequisites

Install Homebrew

Homebrew is a package manager for macOS. When it needs to install software from third-party websites. To install it, run:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/uninstall)"

Install watchman

React Native uses watchman to detect real-time code changes and it automatically builds and pushes the update to your device without manually refreshing.

brew install watchman

Install Java JRE and JDK

There is a risk of react-native build failure if you don’t have a complete installation of Java. Downloading Android Studio is not enough since it comes bundled with its own JRE.

brew install --cask adoptopenjdk/openjdk/adoptopenjdk8

Install React Native

With React Native, you can write an application in Javascript and then the React Native Compiler will convert your Javascript code into native code for iOS and Android environments. React Native command line interface can be installed using npm as below.

npm install -g react-native-cli

Android development prerequisites

Download and install Android Studio, choose the version of your operating system.

When Android Studio is installed, open it.

Android Studio Window
Fig. 1: Android Studio Window

Then go to settings => Appearance & Behavior => System Settings => Android SDK and check the “Show Package Details” checkbox on the bottom right of the windows.

Android Studio Settings
Fig. 2: Android Studio Settings

Install the latest SDK version. To do so, select the packages shown below and click apply.

Android Studio SDK Settings
Fig. 3: Android Studio SDK Settings

Set the environnement variables

If you are using bash, put the environment variable into the bash_profile as below:

cd ~/
touch ~/.bash_profile;
open -e .bash_profile
export ANDROID_HOME=$HOME/Library/Android/sdk
export PATH=$PATH:$ANDROID_HOME/emulator
export PATH=$PATH:$ANDROID_HOME/tools
export PATH=$PATH:$ANDROID_HOME/tools/bin
export PATH=$PATH:$ANDROID_HOME/platform-tools

Do the same if you are using zsh or anything else. Remember the file will be named differently (eg. zsh => .zprofile)

Mobile App Build

Now that we have set up the prerequisites, you can now create the application. In this integration, we will use the ethereum application.

Project Initialization

First, open a terminal and create a new project. For this tutorial the project will be named “ledgerApp”.

Run:

react-native init ledgerApp
cd ledgerApp
Tip
During the initialization, it is installing required 'CocoaPods' dependencies and it may take time.

Code Implementation

Run:

mkdir src
touch polyfill.js
touch src/DeviceItem.js
touch src/DeviceSelectionScreen.js
touch src/ShowAddressScreen.js

polyfill.js

In “polyfill.js” copy-paste the following code:

global.Buffer = require("buffer").Buffer;

index.js

Then import the polyfill in “index.js” as shown below:

/**
 * @format
 */

import "./polyfill";    //import this
import {AppRegistry} from 'react-native';
import App from './src/App';    //modify this import
import {name as appName} from './app.json';

AppRegistry.registerComponent(appName, () => App);

App.js

Move the file named “App.js” in the “src” folder and copy-paste the following code:

import React, { Component } from "react";

import DeviceSelectionScreen from "./DeviceSelectionScreen";
import ShowAddressScreen from "./ShowAddressScreen";

import TransportBLE from "@ledgerhq/react-native-hw-transport-ble";

// This is helpful if you want to see BLE logs. (only to use in dev mode)

class App extends Component {
  state = {
    transport: null
  };

  onSelectDevice = async device => {
    const transport = await TransportBLE.open(device);
    transport.on("disconnect", () => {
      // Intentionally for the sake of simplicity we use a transport local state
      // and remove it on disconnect.
      // A better way is to pass in the device.id and handle the connection internally.
      this.setState({ transport: null });
    });
    this.setState({ transport });
  };

  render() {
    const { transport } = this.state;
    if (!transport) {
      return <DeviceSelectionScreen onSelectDevice={this.onSelectDevice} />;
    }
    return <ShowAddressScreen transport={transport} />;
  }
}

export default App;

In “DeviceItem.js” copy-paste the following code:

import React, { Component } from "react";
import {
  Text,
  TouchableOpacity,
  StyleSheet,
  ActivityIndicator
} from "react-native";

class DeviceItem extends Component {
  state = {
    pending: false
  };
  onPress = async () => {
    this.setState({ pending: true });
    try {
      await this.props.onSelect(this.props.device);
    } finally {
      this.setState({ pending: false });
    }
  };

  render() {
    const { device } = this.props;
    const { pending } = this.state;
    return (
      <TouchableOpacity
        style={styles.deviceItem}
        onPress={this.onPress}
        disabled={pending}
      >
        <Text style={styles.deviceName}>{device.name}</Text>
        {pending ? <ActivityIndicator /> : null}
      </TouchableOpacity>
    );
  }
}
export default DeviceItem;

const styles = StyleSheet.create({
  deviceItem: {
    paddingVertical: 16,
    paddingHorizontal: 32,
    marginVertical: 8,
    marginHorizontal: 16,
    borderColor: "#ccc",
    borderWidth: 1,
    flexDirection: "row",
    alignItems: "center",
    justifyContent: "space-between"
  },
  deviceName: {
    fontSize: 20,
    fontWeight: "bold"
  }
});

In “DeviceSelectionScreen.js” copy-paste the following code:

import React, { Component } from "react";
import {
  StyleSheet,
  Text,
  View,
  TouchableOpacity,
  FlatList,
  Platform,
  PermissionsAndroid
} from "react-native";
import { Observable } from "rxjs";
import AppEth from "@ledgerhq/hw-app-eth";
import TransportBLE from "@ledgerhq/react-native-hw-transport-ble";
import QRCode from "react-native-qrcode-svg";
import DeviceItem from "./DeviceItem";

const deviceAddition = device => ({ devices }) => ({
  devices: devices.some(i => i.id === device.id)
    ? devices
    : devices.concat(device)
});

class DeviceSelectionScreen extends Component {
  state = {
    devices: [],
    error: null,
    refreshing: false
  };

  async componentDidMount() {
    // NB: this is the bare minimal. We recommend to implement a screen to explain to user.
    if (Platform.OS === "android") {
      await PermissionsAndroid.request(
        PermissionsAndroid.PERMISSIONS.ACCESS_COARSE_LOCATION
      );
    }
    let previousAvailable = false;
    new Observable(TransportBLE.observeState).subscribe(e => {
      if (e.available !== previousAvailable) {
        previousAvailable = e.available;
        if (e.available) {
          this.reload();
        }
      }
    });

    this.startScan();
  }

  componentWillUnmount() {
    if (this.sub) this.sub.unsubscribe();
  }

  startScan = async () => {
    this.setState({ refreshing: true });
    this.sub = new Observable(TransportBLE.listen).subscribe({
      complete: () => {
        this.setState({ refreshing: false });
      },
      next: e => {
        if (e.type === "add") {
          this.setState(deviceAddition(e.descriptor));
        }
        // NB there is no "remove" case in BLE.
      },
      error: error => {
        this.setState({ error, refreshing: false });
      }
    });
  };

  reload = async () => {
    if (this.sub) this.sub.unsubscribe();
    this.setState(
      { devices: [], error: null, refreshing: false },
      this.startScan
    );
  };

  keyExtractor = (item: *) => item.id;

  onSelectDevice = async device => {
    try {
      await this.props.onSelectDevice(device);
    } catch (error) {
      this.setState({ error });
    }
  };

  renderItem = ({ item }: { item: * }) => {
    return <DeviceItem device={item} onSelect={this.onSelectDevice} />;
  };

  ListHeader = () => {
    const { error } = this.state;
    return error ? (
      <View style={styles.header}>
        <Text style={styles.headerTitle}>Sorry, an error occured</Text>
        <Text style={styles.errorTitle}>{String(error.message)}</Text>
      </View>
    ) : (
      <View style={styles.header}>
        <Text style={styles.headerTitle}>Scanning for Bluetooth...</Text>
        <Text style={styles.headerSubtitle}>
          Power up your Ledger Nano X and enter your pin.
        </Text>
      </View>
    );
  };

  render() {
    const { devices, error, refreshing } = this.state;

    return (
      <FlatList
        extraData={error}
        style={styles.list}
        data={devices}
        renderItem={this.renderItem}
        keyExtractor={this.keyExtractor}
        ListHeaderComponent={this.ListHeader}
        onRefresh={this.reload}
        refreshing={refreshing}
      />
    );
  }
}

export default DeviceSelectionScreen;

const styles = StyleSheet.create({
  header: {
    paddingTop: 80,
    paddingBottom: 36,
    alignItems: "center"
  },
  headerTitle: {
    fontSize: 22,
    marginBottom: 16
  },
  headerSubtitle: {
    fontSize: 12,
    color: "#999"
  },
  list: {
    flex: 1
  },
  errorTitle: {
    color: "#c00",
    fontSize: 16,
    marginBottom: 16
  }
});

In “ShowAddressScreen.js” copy-paste the following code:

import React, { Component } from "react";
import { StyleSheet, Text, View } from "react-native";

import AppEth from "@ledgerhq/hw-app-eth";
import TransportBLE from "@ledgerhq/react-native-hw-transport-ble";
import QRCode from "react-native-qrcode-svg";

const delay = ms => new Promise(success => setTimeout(success, ms));

class ShowAddressScreen extends Component {
  state = {
    error: null,
    address: null
  };

  async componentDidMount() {
    while (!this.state.address) {
      if (this.unmounted) return;
      await this.fetchAddress(false);
      await delay(500);
    }
    await this.fetchAddress(true);
  }

  async componentWillUnmount() {
    this.unmounted = true;
  }

  fetchAddress = async verify => {
    const { transport } = this.props;
    try {
      const eth = new AppEth(transport);
      const path = "44'/60'/0'/0/0"; // HD derivation path
      const { address } = await eth.getAddress(path, verify);
      if (this.unmounted) return;
      this.setState({ address });
    } catch (error) {
      // in this case, user is likely not on Ethereum app
      if (this.unmounted) return;
      this.setState({ error });
      return null;
    }
  };

  render() {
    const { address, error } = this.state;

    return (
      <View style={styles.ShowAddressScreen}>
        {!address ? (
          <>
            <Text style={styles.loading}>Loading your Ethereum address...</Text>
            {error ? (
              <Text style={styles.error}>
                A problem occurred, make sure to open the Ethereum application
                on your Ledger Nano X. (
                {String((error && error.message) || error)})
              </Text>
            ) : null}
          </>
        ) : (
          <>
            <Text style={styles.title}>Ledger Live Ethereum Account 1</Text>
            <QRCode value={address} size={300} />
            <Text style={styles.address}>{address}</Text>
          </>
        )}
      </View>
    );
  }
}

export default ShowAddressScreen;

const styles = StyleSheet.create({
  ShowAddressScreen: {
    flex: 1,
    padding: 16,
    alignItems: "center",
    justifyContent: "center"
  },
  error: {
    color: "#c00",
    fontSize: 16
  },
  loading: {
    color: "#999",
    fontSize: 16
  },
  title: {
    fontSize: 22,
    marginBottom: 16
  },
  address: {
    marginTop: 16,
    color: "#555",
    fontSize: 14
  }
});

Your folder must look like this.

Folder of the Application
Fig. 4: Folder of the Application

Dependencies Installation

Run:

npm install --save react-native-qrcode-svg
npm install --save react-native-svg
npm install --save rxjs
npm install --save @ledgerhq/react-native-hw-transport-ble
npm install --save react-native-ble-plx
npx react-native link react-native-ble-plx
npm install --save buffer
npm install --save @ledgerhq/hw-app-eth
Package What does it do?
react-native-qrcode-svg It allows you to create a QR code.
react-native-svg It is a package mandatory to use react-native-qrcode-svg.
rxjs It is a rewrite of "Reactive-Extensions/RxJS" and is the latest production-ready version of RxJS.
@ledgerhq/react-native-hw-transport-ble It provides you with all the methods to interact with your Ledger Nano X with a Bluetooth connexion.
react-native-ble-plx It scans the bluetooth devices.
Buffer
It helps you ask your Ledger device to access the ethereum address.

Package.json dependencies

Now that the dependencies are installed you can find them in the “package.js”. This is how your “package.json” has to look like.

{
  "name": "ledgerApp",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "android": "react-native run-android",
    "ios": "react-native run-ios",
    "start": "react-native start",
    "test": "jest",
    "lint": "eslint ."
  },
  "dependencies": {
    "@ledgerhq/hw-app-eth": "^6.16.2",
    "@ledgerhq/react-native-hw-transport-ble": "^6.15.0",
    "buffer": "^6.0.3",
    "react": "17.0.2",
    "react-native": "0.66.3",
    "react-native-ble-plx": "^2.0.3",
    "react-native-qrcode-svg": "^6.1.1",
    "react-native-svg": "^12.1.1",
    "rxjs": "^7.4.0"
  },
  "devDependencies": {
    "@babel/core": "^7.16.0",
    "@babel/runtime": "^7.16.3",
    "@react-native-community/eslint-config": "^3.0.1",
    "babel-jest": "^27.3.1",
    "eslint": "^8.3.0",
    "jest": "^27.3.1",
    "metro-react-native-babel-preset": "^0.66.2",
    "react-test-renderer": "17.0.2"
  },
  "jest": {
    "preset": "react-native"
  }
}

Build.gradle Modification

In “build.gradle”, in the “android” folder change minSdkVersion = 21 to minSdkVersion = 24.

Build.gradle Modify the minSdkVersion
Fig. 5: Build.gradle Modify the minSdkVersion

You can now test the application you have built.

Mobile App Test

The app testing will be executed on your smartphone because the android studio emulator environment does not allow you to use either Bluetooth or USB connexion.

Tip
Please refer to the information for Android Emulator Limitation .

Enable Developer Settings

To integrate an application on your smartphone you have to enable the developer role. To do that go to Settings > About Phone > Build Number, and tap 7 times on build number to enable the developer settings.

Then go to Settings > System > Advanced > Developer Options and enable the “USB debugging” as well as “Install via USB”

Connect your phone to your comptuer, and run the command below to see if your device is connected:

adb devices

If all goes well, the list of devices is displayed as shown below:

Device Connected On The Machine
Fig. 6: Device Connected On The Machine

Tip
For more information about enabling the developer settings on your android device go to android studio docs .

Start the Development Server

You can now open a terminal, navigate to your “ledgerApp” folder, and start the server by running:

npm start

Install the App on Device

Keep the terminal where “metro” is running open and open a new terminal. In this new terminal go to your app folder:

cd ledgerApp

Run the command below to install the application on your android device. It’s assumed that you have connected your smartphone and your device is recognized by the command adb devices as the Previous Step mentioned.

npm run android

A window will pop up on your android device to install the application. Click on “Yes” to install it and run it.

Mobile Application Installation
Fig. 7: Mobile Application Installation

Launching the Application

When launching the application it will be displayed like the image below. You must have the Bluetooth and location activated.

Application Displayed on Smartphone
Fig. 8: Application Displayed on Smartphone

If this is not what you see, you may get:

Bluetooth Not Authorized App Settings 1
App Settings 2 App Settings 3
Fig. 9: Authorize the Bluetooth

Tip
For more information about enabling the Bluetooth settings on your android device go to the troubleshooting tab.

Pairing the Ledger Nano X

To pair your Ledger Nano X, unlock it.

Nano Code Pin
Fig. 10: Nano Code Pin

Now try to pair the Ledger Nano X to your android smartphone.

Pairing the Ledger Nano X Pairing the Ledger Nano X
Fig. 11: Pairing the Ledger Nano X

Pairing and Launching the Ethereum App on Nano X

When pairing, the pairing code will be displayed on your Ledger Nano X to confirm.

Nano Enter Code Pin
Fig. 12: Nano Enter Code Pin

Nano Application
Fig. 13: Nano Application

Nano Run Application
Fig. 14: Nano Run Application

Now that the pairing is complete, the Nano X is ready with the ethereum application. If all goes well you see the address of your ethereum account displayed.

Address Account Displayed on Smartphone
Fig. 15: Address Account Displayed on Smartphone

Verify the Address

For security purposes, we display on your Nano X the same ethereum address for you to confirm.

Nano Verify Screen
Fig. 16: Nano Verify Screen

Nano Verify Address Screen
Fig. 17: Nano Verify Address Screen

Nano Approve Screen
Fig. 18: Nano Approve Screen

Congratulations you have successfully built your first application connected with Ledger on Android!


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