How to setup Qt to use blueZ bluetooth stack

Question

I am developing on Windows 7 machine but final product will be linux and I am also using Ubuntu virtual machine.

I need to search and connect to a bluetooth device and ran this example but from research it appears Qt Bluetooth APIs doesn't really support windows - which is ok, i need it for linux anyways. The bluetooth device discovery code for reference is:

void MyClass::startDeviceDiscovery()
{

    // Create a discovery agent and connect to its signals
    QBluetoothDeviceDiscoveryAgent *discoveryAgent = new QBluetoothDeviceDiscoveryAgent(this);
    connect(discoveryAgent, SIGNAL(deviceDiscovered(QBluetoothDeviceInfo)),
            this, SLOT(deviceDiscovered(QBluetoothDeviceInfo)));

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

    //...
}

// In your local slot, read information about the found devices
void MyClass::deviceDiscovered(const QBluetoothDeviceInfo &device)
{
    qDebug() << "Found new device:" << device.name() << '(' << device.address().toString() << ')';
}

Now I am using blueZ version 4.x which Qt does support but my app doesn't discover anything in linux as well. I have installed blueZ bluetooth in my virtual machine with:

sudo apt-get install libbluetooth-dev

But how do I tell Qt/Qt-Creator to use the blueZ bluetooth stack? How does Qt builds against the blueZ library?

Update

I posted this question nearly 3 years ago and I believe the version was Qt 5.4 but if anyone wants to post a solution, please post it to the latest version of Qt so it can benefit others. As far as I recall, I believe I had found out that Qt supported bluetooth only on linux but not windows. Its implementation on Windows was just a stub.

Answer 1

Is the posted code the actual used code? (next time provide a MCVE ). Which version of QT are you running?

If yes, the problem is that discoveryAgent becomes null at the end of startDeviceDiscovery . For the compiler it's legit, but it's actually a logic error.

Possible solutions could be:

1. implement a class that wrap all the set up and stuff to perform a discovery
2. make discoveryAgent a class member

A faster way to try it out is a Qt console application

btdiscover.pro

QT -= gui
QT += bluetooth # Add it in your .pro file

CONFIG += c++11 console
CONFIG -= app_bundle

DEFINES += QT_DEPRECATED_WARNINGS

SOURCES += main.cpp

main.cpp

#include <QCoreApplication>
#include <QBluetoothServiceDiscoveryAgent>
#include <QBluetoothDeviceInfo>
#include <QDebug>
#include <QObject>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QBluetoothDeviceDiscoveryAgent *discoveryAgent = new QBluetoothDeviceDiscoveryAgent();

    // Connect the signal to a lambda function
    // The 3rd param is a dummy one, in real life application it will be an instance that point to the slot (4th param) owner
    QObject::connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::deviceDiscovered, new QObject(),
            [](const QBluetoothDeviceInfo &device){
        qInfo() << QString("Device found!! Its name is %1 and its MAC is %2").arg(device.name(), device.address().toString());
    });

    // Stop after 5000 mS
    discoveryAgent->setLowEnergyDiscoveryTimeout(5000);
    // Start the discovery process
    discoveryAgent->start(QBluetoothDeviceDiscoveryAgent::LowEnergyMethod);

    return a.exec();
}

In my case the program outputs the following lines:

"Device found!! Its name is IO_EXP and its MAC is 00:XX:XX:XX:XX:A1"
"Device found!! Its name is IO_EXP and its MAC is 00:XX:XX:XX:XX:57"

I compiled the code with Qt 5.11.1

Here there is a step-by-step guide by QT to getting started.

Moreover, as cited here , on Linux, QT uses Bluez.