Bluetooth Low Energy Scanner

An application designed to browse the content of Bluetooth Low Energy peripheral devices. The example demonstrates the use of all Qt Bluetooth Low Energy classes.

The Bluetooth Low Energy Scanner Example shows how to develop Bluetooth Low Energy applications using the Qt Bluetooth API . The application covers scanning for Low Energy devices, scanning their services and reading the service characteristics and descriptors.

The example introduces the following Qt classes:

• QLowEnergyController
• QLowEnergyService
• QLowEnergyCharacteristic
• QLowEnergyDescriptor

The example can be used with any arbitrary Bluetooth Low Energy peripheral device. It creates a snapshot of all services, characteristics and descriptors and presents them to the user. Therefore the application provides an easy way of browsing the content offered by a peripheral device.

运行范例

要运行范例从 Qt Creator ，打开 欢迎 模式，然后选择范例从 范例 。更多信息，拜访 构建和运行范例 .

Requesting Permission to use Bluetooth

On certain platforms, it is required to explicitly grant permissions for using Bluetooth. The example uses BluetoothPermission QML object to check and request the permissions, if required:

BluetoothPermission {
    id: permission
    communicationModes: BluetoothPermission.Access
    onStatusChanged: {
        if (permission.status === Qt.PermissionStatus.Denied)
            Device.update = "Bluetooth permission required"
        else if (permission.status === Qt.PermissionStatus.Granted)
            devicesPage.toggleDiscovery()
    }
}
					

The permission request dialog is triggered when the user tries to start the device discovery, and the permission status is Undetermined :

onButtonClick: {
    if (permission.status === Qt.PermissionStatus.Undetermined)
        permission.request()
    else if (permission.status === Qt.PermissionStatus.Granted)
        devicesPage.toggleDiscovery()
}
					

The device discovery starts if the permission is granted by the user. Otherwise the application is non-functional.

Scanning for Devices

The first step is to find all peripheral devices. The devices can be found using the QBluetoothDeviceDiscoveryAgent class. The discovery process is started using start (). Each new device is advertised via the deviceDiscovered () signal:

discoveryAgent = new QBluetoothDeviceDiscoveryAgent(this);
discoveryAgent->setLowEnergyDiscoveryTimeout(25000);
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::deviceDiscovered,
        this, &Device::addDevice);
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::errorOccurred,
        this, &Device::deviceScanError);
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished,
        this, &Device::deviceScanFinished);
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::canceled,
        this, &Device::deviceScanFinished);
discoveryAgent->start(QBluetoothDeviceDiscoveryAgent::LowEnergyMethod);
					

The below addDevice() slot is triggered as a reaction to the discovery of a new device. It filters all found devices which have the QBluetoothDeviceInfo::LowEnergyCoreConfiguration flag and adds them to a list which is shown to the user. The deviceDiscovered () signal may be emitted multiple times for the same device as more details are discovered. Here we match these device discoveries so that the user only sees the individual devices:

void Device::addDevice(const QBluetoothDeviceInfo &info)
{
    if (info.coreConfigurations() & QBluetoothDeviceInfo::LowEnergyCoreConfiguration) {
        auto devInfo = new DeviceInfo(info);
        auto it = std::find_if(devices.begin(), devices.end(),
                               [devInfo](DeviceInfo *dev) {
                                   return devInfo->getAddress() == dev->getAddress();
                               });
        if (it == devices.end()) {
            devices.append(devInfo);
        } else {
            auto oldDev = *it;
            *it = devInfo;
            delete oldDev;
        }
        emit devicesUpdated();
    }
}
					

The list of devices may look like in the image below.

注意： It is a prerequisite that the remote devices actively advertise their presence.

if (!controller) {
    // Connecting signals and slots for connecting to LE services.
    controller = QLowEnergyController::createCentral(currentDevice.getDevice(), this);
    connect(controller, &QLowEnergyController::connected,
            this, &Device::deviceConnected);
    connect(controller, &QLowEnergyController::errorOccurred, this, &Device::errorReceived);
    connect(controller, &QLowEnergyController::disconnected,
            this, &Device::deviceDisconnected);
    connect(controller, &QLowEnergyController::serviceDiscovered,
            this, &Device::addLowEnergyService);
    connect(controller, &QLowEnergyController::discoveryFinished,
            this, &Device::serviceScanDone);
}
if (isRandomAddress())
    controller->setRemoteAddressType(QLowEnergyController::RandomAddress);
else
    controller->setRemoteAddressType(QLowEnergyController::PublicAddress);
controller->connectToDevice();
				

controller->discoverServices();
				

QLowEnergyService *service = controller->createServiceObject(serviceUuid);
if (!service) {
    qWarning() << "Cannot create service for uuid";
    return;
}
				

connect(service, &QLowEnergyService::stateChanged,
        this, &Device::serviceDetailsDiscovered);
service->discoverDetails();
setUpdate(u"Back\n(Discovering details...)"_s);
				

const QList<QLowEnergyCharacteristic> chars = service->characteristics();
for (const QLowEnergyCharacteristic &ch : chars) {
    auto cInfo = new CharacteristicInfo(ch);
    m_characteristics.append(cInfo);
}
				

QString name = m_characteristic.name();
if (!name.isEmpty())
    return name;
// find descriptor with CharacteristicUserDescription
const QList<QLowEnergyDescriptor> descriptors = m_characteristic.descriptors();
for (const QLowEnergyDescriptor &descriptor : descriptors) {
    if (descriptor.type() == QBluetoothUuid::DescriptorType::CharacteristicUserDescription) {
        name = descriptor.value();
        break;
    }
}