How to connect to two LE peripherals

LubomirBogdanov

Hi guys,
I've successfully connected my Qt application with a LE embedded device. I can read from it and I can write to it. I'm using Qt Creator 6.3.1 and Windows 11.

However my task is to connect to several peripherals.

My question is: do I have to make separate slots for each peripheral or is there another way to do it?

Currently I'm trying to avoid this:

void bluetooth_controller::scan_for_characteristics(qsizetype device_index, qsizetype service_index){
    
    service_object[0] = ble_central->createServiceObject(ble_service_uuids.at(0), this);

    connect(service_object[0], &QLowEnergyService::stateChanged, this, &bluetooth_controller::on_central_state_changed);
    connect(service_object[0], &QLowEnergyService::characteristicChanged, this, &bluetooth_controller::on_central_characteristic_changed);
    connect(service_object[0], &QLowEnergyService::characteristicWritten, this, &bluetooth_controller::on_central_characteristic_written);
    connect(service_object[0], &QLowEnergyService::errorOccurred, this, &bluetooth_controller::on_central_chracteristic_error);
    connect(service_object[0], &QLowEnergyService::characteristicRead, this, &bluetooth_controller::on_central_chracteristic_read);
    connect(service_object[0], &QLowEnergyService::descriptorRead, this, &bluetooth_controller::on_central_chracteristic_descriptor_read);
    connect(service_object[0], &QLowEnergyService::descriptorWritten, this, &bluetooth_controller::on_central_chracteristic_descriptor_written);

    service_object[0]->discoverDetails();

    service_object[1] = ble_central->createServiceObject(ble_service_uuids.at(1), this);

    connect(service_object[1], &QLowEnergyService::stateChanged, this, &bluetooth_controller::on_central_state_changed);
    connect(service_object[1], &QLowEnergyService::characteristicChanged, this, &bluetooth_controller::on_central_characteristic_changed);
    connect(service_object[1], &QLowEnergyService::characteristicWritten, this, &bluetooth_controller::on_central_characteristic_written);
    connect(service_object[1], &QLowEnergyService::errorOccurred, this, &bluetooth_controller::on_central_chracteristic_error);
    connect(service_object[1], &QLowEnergyService::characteristicRead, this, &bluetooth_controller::on_central_chracteristic_read);
    connect(service_object[1], &QLowEnergyService::descriptorRead, this, &bluetooth_controller::on_central_chracteristic_descriptor_read);
    connect(service_object[1], &QLowEnergyService::descriptorWritten, this, &bluetooth_controller::on_central_chracteristic_descriptor_written);

    service_object[1]->discoverDetails();
}

given that the objects are:

    QLowEnergyController *ble_central = nullptr;
    QList<QBluetoothDeviceInfo> ble_devices;
    QList<QBluetoothUuid> ble_service_uuids;
    QLowEnergyService *service_object[16];

Thanks in advance!
L. B.

Paul Colby

Hi @LubomirBogdanov,

You can, if you wish, use the same slots. For example, as you already have:

connect(service_object[0], &QLowEnergyService::stateChanged, this, &bluetooth_controller::on_central_state_changed);
...
connect(service_object[1], &QLowEnergyService::stateChanged, this, &bluetooth_controller::on_central_state_changed);

Then, in bluetooth_controller::on_central_state_changed(), you can do something like:

void bluetooth_controller::on_central_state_changed(...)
{
    QLowEnergyService * service = qobject_cast<QLowEnergyService *>(sender());
    if (service != nullptr) {
        ...
    }
}

See QObject::sender() and qobject_cast for details.

Cheers.

J.Hilk

@LubomirBogdanov depends,

what I would do is, make a new class, that accepts a QLowEnergyService as an object.

than you can do your connects and operations all in that one. No need for other slots.

If you insist on doing everything inside bluetooth_controller you should consider using a Lambda, as 4th parameter of QObject::connect.
That way you can call the function with additional parameters. For example a pointer to the object. That way you can decide in the function what to do

I would however discourage the use of sender() because violates the object-oriented principle of modularity and the return value of this function is not valid when the slot is called via a Qt::DirectConnection from a thread different from this object's thread

https://doc.qt.io/qt-6/qobject.html#sender