Qt Bluetooth unable to connect socket to device

Question

I'm trying to establish bluetooth connection between laptop and Samsung Smart Touch Remote. My issue is that I can't connect socket to device(socket is always in "Host lookup state"):

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    // Create a discovery agent and connect to its signals
    QBluetoothDeviceDiscoveryAgent *discoveryAgent = new QBluetoothDeviceDiscoveryAgent(this);
    connect(discoveryAgent, SIGNAL(deviceDiscovered(const QBluetoothDeviceInfo&)),
        this, SLOT(deviceDiscovered(const QBluetoothDeviceInfo&)));

    // Start a discovery
    discoveryAgent->start();
}

void MainWindow::deviceDiscovered(const QBluetoothDeviceInfo &device)
{
    socket = new QBluetoothSocket(QBluetoothServiceInfo::RfcommProtocol, this);
    socket->connectToService(QBluetoothAddress(device.address()),
                                     QBluetoothUuid(QBluetoothUuid::SerialPort));
    connect(socket, SIGNAL(error(QBluetoothSocket::SocketError)),
                    this, SLOT(socketError(QBluetoothSocket::SocketError)));
    connect(socket, SIGNAL(connected()), this, SLOT(socketConnected()));
    connect(socket, SIGNAL(disconnected()), this, SLOT(socketDisconnected()));
    connect(socket, SIGNAL(readyRead()), this, SLOT(socketRead()));
    connect(socket, SIGNAL(stateChanged(QBluetoothSocket::SocketState)), this, SLOT(socketStateChanged()));
}

void MainWindow::socketRead()
{
    QByteArray receivedData = socket->readAll();
    QMessageBox msg;
    msg.setText(QString(receivedData));
    msg.exec();
}

void MainWindow::socketConnected()
{
    qDebug() << "Socket connected";
    qDebug() << "Local: "
             << socket->localName()
             << socket->localAddress().toString()
             << socket->localPort();
    qDebug() << "Peer: "
             << socket->peerName()
             << socket->peerAddress().toString()
             << socket->peerPort();
}

void MainWindow::socketDisconnected()
{
    qDebug() << "Socket disconnected";
    socket->deleteLater();
}

void MainWindow::socketError(QBluetoothSocket::SocketError error)
{
    qDebug() << "Socket error: " << error;
}

void MainWindow::socketStateChanged()
{
    int socketState = socket->state();
    QMessageBox msg;
    if(socketState == QAbstractSocket::UnconnectedState)
    {
        msg.setText("unconnected");
    }
    else if(socketState == QAbstractSocket::HostLookupState)
    {
        msg.setText("host lookup");
    }
    else if(socketState == QAbstractSocket::ConnectingState )
    {
        msg.setText("connecting");
    }
    else if(socketState == QAbstractSocket::ConnectedState)
    {
        msg.setText("connected");
    }
    else if(socketState == QAbstractSocket::BoundState)
    {
        msg.setText("bound");
    }
    else if(socketState == QAbstractSocket::ClosingState)
    {
        msg.setText("closing");
    }
    else if(socketState == QAbstractSocket::ListeningState)
    {
        msg.setText("listening");
    }
    msg.exec();
}

Can someone please tell me what I'm doing wrong?

Answer 1

I had the samme issue. The fix was to use a port 1 in argument to socket->connectToService(addr, 1).

This tells SDP to use connection as channel via SDP.

Answer 2

Have you tried to open a COM port on your Laptop which is connected to the Laptop's bluetooth module?

You can go to Bluetooth settings -> Com Ports -> Add a new com port. Then open this Port using hypertermical or Teraterm. Now try to connect from your Android phone...

Hope this works!