Creación de una aplicación Bluetooth para ESP32 con React Native

Etiquetas: Bluetooth, Comunicación inalámbrica, ESP32, React Native

Vamos a ver cómo crear una aplicación React Native que permita la comunicación Bluetooth entre un dispositivo Android y un ESP32. Usamos React Native para desarrollar un terminal Bluetooth en Android que se comunica con un ESP32 NodeMCU. El NodeMCU se utiliza para probar nuestra aplicación con un objeto conectado, pero la aplicación puede funcionar con cualquier dispositivo Bluetooth.

Hardware

Un ordenador con React Native y Node.js instalados
Un dispositivo Android con Bluetooth
Un cable USB para conectar el ordenador al dispositivo
Un dispositivo Bluetooth (ESP32)

Código de gestión Bluetooth para ESP32

Para probar la aplicación React Native, vamos a utilizar el código de gestión de Bluetooth para ESP32.

#include "BluetoothSerial.h"

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

BluetoothSerial SerialBT;

void callback(esp_spp_cb_event_t event, esp_spp_cb_param_t *param) {
  if (event == ESP_SPP_SRV_OPEN_EVT) {
    Serial.println("Client Connected");
  }

  if (event == ESP_SPP_CLOSE_EVT ) {
    Serial.println("Client disconnected");
    //SerialBT.flush();
    //SerialBT.disconnect();
    //SerialBT.end();
    //SerialBT.begin("ESP32BT");
    ESP.restart(); // needed to be able to reconnect
  }
}

void setup() {
  Serial.begin(115200);

  SerialBT.register_callback(callback);
  SerialBT.begin("ESP32BT"); //Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");
}

String msg = "";
void loop() {
  /*if (Serial.available()) {
    SerialBT.write(Serial.read());
    }*/

  readSerialPort();
  //Send data to slave
  if (msg != "") {
    Serial.println(msg);
    SerialBT.println(msg);
    msg = "";
  }

  if (SerialBT.available()) {
    Serial.write(SerialBT.read());
  }
  delay(20);
}

void readSerialPort() {
  while (Serial.available()) {
    delay(10);
    if (Serial.available() > 0) {
      char c = Serial.read();  //gets one byte from serial buffer
      msg += c; //add to String
    }
  }
  Serial.flush(); //clean buffer
}

Añadimos la función callback a la gestión de Bluetooth para detectar la desconexión y reiniciar el ESP32

SerialBT.register_callback(callback);

Nota: es necesario reiniciar el ESP32 para volver a conectar el Bluetooth porque, obviamente, el BluetoothSocket no se cierra al desconectarse.

Aplicación React Native para la gestión de Bluetooth

Para gestionar la comunicación Bluetooth (clásica) en el dispositivo Android, utilizamos la biblioteca react-native-bluetooth-classic

npm install react-native-bluetooth-classic --save

Para configurar el proyecto de aplicación, siga el tutorial anterior.

En el archivo App.tsx, para utilizar la biblioteca la importamos utilizando el comando

import RNBluetoothClassic, {BluetoothDevice,} from 'react-native-bluetooth-classic';

Estamos creando un componente funcional que contendrá los elementos que necesitamos para gestionar la comunicación Bluetooth

const BluetoothClassicTerminal = () =>  {
  const [devices, setDevices] = useState<any[]>([]);
  const [paired, setPaired] = useState<any[]>([]);
  const [selectedDevice, setSelectedDevice] = useState<BluetoothDevice>();
  const [messageToSend, setMessageToSend] = useState("");
  const [receivedMessage, setReceivedMessage] = useState("");
  const [isConnected, setIsConnected] = useState(false);
  const [intervalId, setIntervalId] = useState<NodeJS.Timer>();

N.B.: es posible crear un componente derivado de ReactNative.Components

Gestión de permisos

Para descubrir y conectarte a dispositivos Bluetooth, necesitas al menos 3 permisos:

BLUETOOTH_SCAN
BLUETOOTH_CONNECT
ACCESS_FINE_LOCATION

N.B.: estos permisos dependen de la versión y el SO utilizados

Estas son las etiquetas que hay que añadir al archivo AndroidManifest.xml

  <uses-permission android:name="android.permission.INTERNET" />
  <uses-permission android:name="android.permission.BLUETOOTH" />
  <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
  <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
  <uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
  <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
  <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

En el archivo App.tsx, creamos la función requestBluetoothPermission()

async function requestBluetoothPermission(){
      try {
        const grantedScan = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_SCAN,
          {
            title: 'Bluetooth Scan Permission',
            message: 'This app needs Bluetooth Scan permission to discover devices.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
  
        const grantedConnect = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_CONNECT,
          {
            title: 'Bluetooth Connect Permission',
            message: 'This app needs Bluetooth Connect permission to connect to devices.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
      
        const grantedLocation = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
          {
            title: 'Fine Location Permission',
            message: 'This app needs to know location of device.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
  
        if (
          grantedScan === PermissionsAndroid.RESULTS.GRANTED &&
          grantedConnect === PermissionsAndroid.RESULTS.GRANTED &&
          grantedLocation === PermissionsAndroid.RESULTS.GRANTED
        ) {
          console.log('Bluetooth permissions granted');
          // Vous pouvez maintenant commencer la découverte et la connexion Bluetooth ici.
        } else {
          console.log('Bluetooth permissions denied');
        }
      
      
      } catch (err) {
        console.warn(err);
      }
    }

Función de gestión de Bluetooth

Las funciones de gestión de Bluetooth son las siguientes:

descubrir dispositivos bluetooth startDeviceDiscovery() (utilizo dispositivos emparejados)
conectar con el dispositivo connectToDevice()
desconectar disconnect()
enviar mensajes sendMessage()
leer mensajes de la comunicación readData()

N.B.: la documentación de la biblioteca menciona el uso de un oyente onDataReceived, que no he conseguido utilizar. Por tanto, he introducido la función readData y un Interval para recuperar los datos.

const checkBluetoothEnabled = async () => {
    try {
      const enabled = await RNBluetoothClassic.isBluetoothEnabled();
      if (!enabled) {
        await RNBluetoothClassic.requestBluetoothEnabled();
      }
      
    } catch (error) {
      console.error('Bluetooth Classic is not available on this device.');
    }
  }
  
  const startDeviceDiscovery = async () => {
    console.log("searching for devices...");
    try {
      const paired = await RNBluetoothClassic.getBondedDevices();
      console.log("Bonded peripherals: " + paired.length);
      setPaired(paired);
    } catch (error) {
      console.error('Error bonded devices:', error);
    }
  }

  const connectToDevice = async (device: BluetoothDevice) => {
    try {
      console.log("Connecting to device");
      let connection = await device.isConnected();
      if (!connection) {
        console.log("Connecting to device");
        await device.connect({
          connectorType: "rfcomm",
          DELIMITER: "\n",
          DEVICE_CHARSET: Platform.OS === "ios" ? 1536 : "utf-8",
        });
      }
      setSelectedDevice(device);
      setIsConnected(true);
      console.log("is connected : ",isConnected);
      //device.onDataReceived((data) => this.readData());
      //const intervalId = setInterval(() => {readData();}, 100);
      //setIntervalId(intervalId);

      
    } catch (error) {
      console.error('Error connecting to device:', error);
    }
  }


const sendMessage = async () => {
  if(selectedDevice && isConnected){
    console.log("isConnected in message",isConnected);
    try {
      await selectedDevice.write(messageToSend);
      
    } catch (error) {
      console.error('Error sending message:', error);
    }
  }
}

const readData = async () => {  
  if (selectedDevice && isConnected) {
    try {
        let message = await selectedDevice.read();
        if(message){
          message = message.trim();
          if (message !== "" && message !== " "){
            if(receivedMessage.length>300){
              setReceivedMessage("");
            }
            setReceivedMessage(receivedMessage => receivedMessage + message +"\n" );
          }
        }

    } catch (error) {
      console.error('Error reading message:', error);
    }
  }
}

useEffect(() => {
  let intervalId: string | number | NodeJS.Timer | undefined;
  if (selectedDevice && isConnected) {
    intervalId = setInterval(() => readData(), 100);
  }
  return () => {
    clearInterval(intervalId);
  };
}, [isConnected,selectedDevice]);

const disconnect = () => {
  //need to reset esp32 at disconnect
  if(selectedDevice && isConnected){
    try {
      clearInterval(intervalId);
      setIntervalId(undefined);
      
      selectedDevice.clear().then( () => {
        console.log("BT buffer cleared");
      });

      selectedDevice.disconnect().then( () => {
        setSelectedDevice(undefined);
        setIsConnected(false);
        setReceivedMessage("");
        console.log("Disconnected from device");
      });

    } catch (error) {
      console.error('Error disconnecting:', error);
    }
  }
}

La función de representación en pantalla

Para la visualización, hemos decidido ponerlo todo en la misma pantalla. Habrá :

Un título
La lista de dispositivos que sólo aparece si no estás conectado (!isConnected &&)
Una inserción de tipo terminal de comunicación que sólo aparece si está conectado (selectedDevice && isConnected &&)
- TextInput para escribir el mensaje a enviar messageToSend
- Un botón de envío
- Un cuadro de texto para mostrar receivedMessage
- Un botón de desconexión

    return (
      <View>
      <Text
            style={{
              fontSize: 30,
              textAlign: 'center',
              borderBottomWidth: 1,
            }}>
            AC Bluetooth Terminal
          </Text>
        <ScrollView>

          {!isConnected && (
          <>
          {/*
          <Text>Available Devices:</Text>
          {devices.map((device) => (
            <Button
              key={device.id}
              title={device.name || 'Unnamed Device'}
              onPress={() => this.connectToDevice(device)}
            />
          ))}
          */}
          <Text>Paired Devices:</Text>
          {paired.map((pair: BluetoothDevice,i) => (
                      <View  key={i}
                      style={{
                        flexDirection: 'row',
                        justifyContent: 'space-between',
                        marginBottom: 2,
                      }}>
                      <View style={styles.deviceItem}>
                        <Text style={styles.deviceName}>{pair.name}</Text>
                        <Text style={styles.deviceInfo}>{pair.id}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() =>
                          isConnected
                            ?  disconnect()
                            :  connectToDevice(pair)
                        }
                        style={styles.deviceButton}>
                        <Text
                          style={[
                            styles.scanButtonText,
                            {fontWeight: 'bold', fontSize: 12},
                          ]}>
                          {isConnected ? 'Disconnect' : 'Connect'}
                        </Text>
                      </TouchableOpacity>
                    </View>
          ))}
          </>  
          )}
          {selectedDevice && isConnected && (
            <>
              <View
                      style={{
                        flexDirection: 'row',
                        justifyContent: 'space-between',
                        margin: 5,
                      }}>
                      <View style={styles.deviceItem}>
                        <Text style={styles.deviceName}>{selectedDevice.name}</Text>
                        <Text style={styles.deviceInfo}>{selectedDevice.id}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() =>
                          isConnected
                            ?  disconnect()
                            :  connectToDevice(selectedDevice)
                        }
                        style={styles.deviceButton}>
                        <Text
                          style={styles.scanButtonText}>
                          {isConnected ? 'Disconnect' : 'Connect'}
                        </Text>
                      </TouchableOpacity>
                    </View>

          <View
              style={{
                flexDirection: 'row',
                justifyContent: 'space-between',
                margin: 5,
              }}>        
              <TextInput
                style={{
                  backgroundColor: '#888888',
                  margin: 2,
                  borderRadius: 15,
                  flex:3,
                  }}
                placeholder="Enter a message"
                value={messageToSend}
                onChangeText={(text) => setMessageToSend(text )}
              />
              <TouchableOpacity
                        onPress={() => sendMessage()
                        }
                        style={[styles.sendButton]}>
                        <Text
                          style={[
                            styles.scanButtonText,
                          ]}>
                          SEND
                        </Text>
                      </TouchableOpacity>
        </View>
              <Text>Received Message:</Text>
              <TextInput
              editable = {false}
              multiline
              numberOfLines={20}
              maxLength={300}
                style={{
                  backgroundColor: '#333333',
                  margin: 10,
                  borderRadius: 2,
                  borderWidth: 1,
                  borderColor: '#EEEEEE',
                  textAlignVertical: 'top',
                  }} >
                    {receivedMessage}
              </TextInput>
              
            </>
          )}
        </ScrollView>
      </View>
    );

Resultados

Como el emparejamiento no está gestionado por la aplicación, el ESP32 debe estar emparejado antes de utilizar la aplicación. Una vez que el código se ha cargado en el ESP32, puede iniciar la aplicación en el teléfono mediante el comando

npx react-native start

react-native-bluetooth-discovery Creación de una aplicación Bluetooth para ESP32 con React Native

react-native-bluetooth-terminal Creación de una aplicación Bluetooth para ESP32 con React Native

react-native-bluetooth-esp32-monitor Creación de una aplicación Bluetooth para ESP32 con React Native

Código completo de la aplicación React Native

/**
 * https://kenjdavidson.com/react-native-bluetooth-classic/
 */

import React, {useState, useEffect} from 'react';
import {   
  StyleSheet,
  Dimensions,
  View, ScrollView, Text,
   Button, TextInput,PermissionsAndroid,Platform, TouchableOpacity } from 'react-native';
import RNBluetoothClassic, {BluetoothDevice,} from 'react-native-bluetooth-classic';

const BluetoothClassicTerminal = () =>  {
  const [devices, setDevices] = useState<any[]>([]);
  const [paired, setPaired] = useState<any[]>([]);
  const [selectedDevice, setSelectedDevice] = useState<BluetoothDevice>();
  const [messageToSend, setMessageToSend] = useState("");
  const [receivedMessage, setReceivedMessage] = useState("");
  const [isConnected, setIsConnected] = useState(false);
  const [intervalId, setIntervalId] = useState<NodeJS.Timer>();
  
  
  /*const [state, setState] = useState({
    devices: [],
    paired: [],
    selectedDevice: null,
    messageToSend: "",
    receivedMessage: "",
    isConnected: false,
    intervalId: null,
  })*/




  const checkBluetoothEnabled = async () => {
    try {
      const enabled = await RNBluetoothClassic.isBluetoothEnabled();
      if (!enabled) {
        await RNBluetoothClassic.requestBluetoothEnabled();
      }
      
    } catch (error) {
      console.error('Bluetooth Classic is not available on this device.');
    }
  }
  
  const startDeviceDiscovery = async () => {
    console.log("searching for devices...");
    try {
      const paired = await RNBluetoothClassic.getBondedDevices();
      console.log("Bonded peripherals: " + paired.length);
      setPaired(paired);
    } catch (error) {
      console.error('Error bonded devices:', error);
    }
    
    /*try {
      const devices = await RNBluetoothClassic.startDiscovery();
      this.setState({ devices });
      console.log("Discovered peripherals: " + devices.length);
    } catch (error) {
      console.error('Error discovering devices:', error);
    }*/
  }

  const connectToDevice = async (device: BluetoothDevice) => {
    try {
      console.log("Connecting to device");
      let connection = await device.isConnected();
      if (!connection) {
        console.log("Connecting to device");
        await device.connect({
          connectorType: "rfcomm",
          DELIMITER: "\n",
          DEVICE_CHARSET: Platform.OS === "ios" ? 1536 : "utf-8",
        });
      }
      setSelectedDevice(device);
      setIsConnected(true);
      console.log("is connected : ",isConnected);
      //device.onDataReceived((data) => this.readData());
      //const intervalId = setInterval(() => {readData();}, 100);
      //setIntervalId(intervalId);

      
    } catch (error) {
      console.error('Error connecting to device:', error);
    }
  }

    /*async onReceivedData() {
  const { selectedDevice, receivedMessage } = this.state;
  //console.log("event : recived message", event);
  try{
    //const message = await selectedDevice.read();
    console.log("reieved msg from", selectedDevice.name);
    const messages = await selectedDevice.available();
  if (messages.length > 0) {
    console.log("msg waiting : ", messages.length);
  }
    //this.setState({ receivedMessage: message.data });
  } catch (error) {
    console.error('Error receiving data:', error);
  }
}*/

const sendMessage = async () => {
  if(selectedDevice && isConnected){
    console.log("isConnected in message",isConnected);
    try {
      await selectedDevice.write(messageToSend);
      
    } catch (error) {
      console.error('Error sending message:', error);
    }
  }
}

/*const readData = async () => {  
  console.log("reading data connected", isConnected);
  if(selectedDevice && isConnected){
    try {
      console.log("reading data from", selectedDevice.name);
      //const available = await selectedDevice.available();
      //if (available>1){
        let message = await selectedDevice.read();
        if(message){
          message = message.trim();
          if (message !== "" && message !== " "){
            console.log("reading data from", selectedDevice.name);
            //console.log(" available : ",  available);
            //console.log("available", selectedDevice.available());
            //console.log("read", selectedDevice.read());
            setReceivedMessage(receivedMessage + message +"\n" );
            console.log('message', message);
            console.log('message', receivedMessage);
            
          }
        }
    //  }

    } catch (error) {
      //console.log("isConnected",isConnected);
      //console.log("selectedDevice",selectedDevice);
      console.error('Error reading message:', error);
    }
  }
}*/

const readData = async () => {  
  if (selectedDevice && isConnected) {
    try {
      //const available = await selectedDevice.available();
      //if (available>1){
        let message = await selectedDevice.read();
        if(message){
          message = message.trim();
          if (message !== "" && message !== " "){
            if(receivedMessage.length>300){
              setReceivedMessage("");
            }
            setReceivedMessage(receivedMessage => receivedMessage + message +"\n" );
          }
        }
    //  }

    } catch (error) {
      //console.log("isConnected",isConnected);
      //console.log("selectedDevice",selectedDevice);
      console.error('Error reading message:', error);
    }
  }
}

useEffect(() => {
  let intervalId: string | number | NodeJS.Timer | undefined;
  if (selectedDevice && isConnected) {
    intervalId = setInterval(() => readData(), 100);
  }
  return () => {
    clearInterval(intervalId);
  };
}, [isConnected,selectedDevice]);

const disconnect = () => {
  //need to reset esp32 at disconnect
  if(selectedDevice && isConnected){
    try {
      clearInterval(intervalId);
      setIntervalId(undefined);
      
      selectedDevice.clear().then( () => {
        console.log("BT buffer cleared");
      });

      selectedDevice.disconnect().then( () => {
        setSelectedDevice(undefined);
        setIsConnected(false);
        setReceivedMessage("");
        console.log("Disconnected from device");
      });

      /*RNBluetoothClassic.unpairDevice(uuid).then( () => {
        console.log("Unpaired from device");
      });
      
      RNBluetoothClassic.pairDevice(uuid).then( () => {
        console.log("paired from device");
      });*/



    } catch (error) {
      console.error('Error disconnecting:', error);
    }
  }
}
  useEffect(() => {

    async function requestBluetoothPermission(){
      try {
        const grantedScan = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_SCAN,
          {
            title: 'Bluetooth Scan Permission',
            message: 'This app needs Bluetooth Scan permission to discover devices.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
  
        const grantedConnect = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.BLUETOOTH_CONNECT,
          {
            title: 'Bluetooth Connect Permission',
            message: 'This app needs Bluetooth Connect permission to connect to devices.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
      
        const grantedLocation = await PermissionsAndroid.request(
          PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
          {
            title: 'Fine Location Permission',
            message: 'This app needs to know location of device.',
            buttonPositive: 'OK',
            buttonNegative: 'Cancel',
          }
        );
  
        if (
          grantedScan === PermissionsAndroid.RESULTS.GRANTED &&
          grantedConnect === PermissionsAndroid.RESULTS.GRANTED &&
          grantedLocation === PermissionsAndroid.RESULTS.GRANTED
        ) {
          console.log('Bluetooth permissions granted');
          // Vous pouvez maintenant commencer la découverte et la connexion Bluetooth ici.
        } else {
          console.log('Bluetooth permissions denied');
        }
      
      
      } catch (err) {
        console.warn(err);
      }
    }

      checkBluetoothEnabled();

      requestBluetoothPermission().then( () => {
        startDeviceDiscovery();
      });
  }, [])


    return (
      <View>
      <Text
            style={{
              fontSize: 30,
              textAlign: 'center',
              borderBottomWidth: 1,
            }}>
            AC Bluetooth Terminal
          </Text>
        <ScrollView>

          {!isConnected && (
          <>
		  
		  <TouchableOpacity
            onPress={() => startDeviceDiscovery()}
            style={[styles.deviceButton]}>
            <Text
                style={[
                    styles.scanButtonText,
                    ]}>
                SCAN
            </Text>
         </TouchableOpacity>
          {/*
          <Text>Available Devices:</Text>
          {devices.map((device) => (
            <Button
              key={device.id}
              title={device.name || 'Unnamed Device'}
              onPress={() => this.connectToDevice(device)}
            />
          ))}
          */}
          <Text>Paired Devices:</Text>
          {paired.map((pair: BluetoothDevice,i) => (
                      <View  key={i}
                      style={{
                        flexDirection: 'row',
                        justifyContent: 'space-between',
                        marginBottom: 2,
                      }}>
                      <View style={styles.deviceItem}>
                        <Text style={styles.deviceName}>{pair.name}</Text>
                        <Text style={styles.deviceInfo}>{pair.id}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() =>
                          isConnected
                            ?  disconnect()
                            :  connectToDevice(pair)
                        }
                        style={styles.deviceButton}>
                        <Text
                          style={[
                            styles.scanButtonText,
                            {fontWeight: 'bold', fontSize: 12},
                          ]}>
                          {isConnected ? 'Disconnect' : 'Connect'}
                        </Text>
                      </TouchableOpacity>
                    </View>
          ))}
          </>  
          )}
          {selectedDevice && isConnected && (
            <>
              <View
                      style={{
                        flexDirection: 'row',
                        justifyContent: 'space-between',
                        margin: 5,
                      }}>
                      <View style={styles.deviceItem}>
                        <Text style={styles.deviceName}>{selectedDevice.name}</Text>
                        <Text style={styles.deviceInfo}>{selectedDevice.id}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() =>
                          isConnected
                            ?  disconnect()
                            :  connectToDevice(selectedDevice)
                        }
                        style={styles.deviceButton}>
                        <Text
                          style={styles.scanButtonText}>
                          {isConnected ? 'Disconnect' : 'Connect'}
                        </Text>
                      </TouchableOpacity>
                    </View>

          <View
              style={{
                flexDirection: 'row',
                justifyContent: 'space-between',
                margin: 5,
              }}>        
              <TextInput
                style={{
                  backgroundColor: '#888888',
                  margin: 2,
                  borderRadius: 15,
                  flex:3,
                  }}
                placeholder="Enter a message"
                value={messageToSend}
                onChangeText={(text) => setMessageToSend(text )}
              />
              <TouchableOpacity
                        onPress={() => sendMessage()
                        }
                        style={[styles.sendButton]}>
                        <Text
                          style={[
                            styles.scanButtonText,
                          ]}>
                          SEND
                        </Text>
                      </TouchableOpacity>
        </View>
              <Text>Received Message:</Text>
              <TextInput
              editable = {false}
              multiline
              numberOfLines={20}
              maxLength={300}
                style={{
                  backgroundColor: '#333333',
                  margin: 10,
                  borderRadius: 2,
                  borderWidth: 1,
                  borderColor: '#EEEEEE',
                  textAlignVertical: 'top',
                  }} >
                    {receivedMessage}
              </TextInput>
              
            </>
          )}
        </ScrollView>
      </View>
    );

};//end of component

const windowHeight = Dimensions.get('window').height;
const styles = StyleSheet.create({
  mainBody: {
    flex: 1,
    justifyContent: 'center',
    height: windowHeight,
  },

  scanButtonText: {
    color: 'white',
    fontWeight: 'bold',
    fontSize: 12,
	textAlign: 'center',
  },
  noDevicesText: {
    textAlign: 'center',
    marginTop: 10,
    fontStyle: 'italic',
  },
  deviceItem: {
    marginBottom: 2,
  },
  deviceName: {
    fontSize: 14,
    fontWeight: 'bold',
  },
  deviceInfo: {
    fontSize: 8,
  },
  deviceButton: {
    backgroundColor: '#2196F3',
    padding: 10,
    borderRadius: 10,
    margin: 2,
    paddingHorizontal: 20,
  },
  sendButton: {
  backgroundColor: '#2196F3',
  padding: 15,
  borderRadius: 15,
  margin: 2,
  paddingHorizontal: 20,
  },
});

export default BluetoothClassicTerminal;