QBluetoothDeviceDiscoveryAgent Class

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() << ')';
}

Member Function Documentation

QBluetoothDeviceDiscoveryAgent::QBluetoothDeviceDiscoveryAgent(QObject *parent = nullptr)

Constructs a new Bluetooth device discovery agent with parent parent.

QBluetoothDeviceDiscoveryAgent::QBluetoothDeviceDiscoveryAgent(const QBluetoothAddress &deviceAdapter, QObject *parent = nullptr)

Constructs a new Bluetooth device discovery agent with parent.

It uses deviceAdapter for the device search. If deviceAdapter is default constructed the resulting QBluetoothDeviceDiscoveryAgent object will use the local default Bluetooth adapter.

If a deviceAdapter is specified that is not a local adapter error() will be set to InvalidBluetoothAdapterError. Therefore it is recommended to test the error flag immediately after using this constructor.

See also error().

[virtual] QBluetoothDeviceDiscoveryAgent::~QBluetoothDeviceDiscoveryAgent()

Destructor for ~QBluetoothDeviceDiscoveryAgent()

[signal] void QBluetoothDeviceDiscoveryAgent::canceled()

This signal is emitted when device discovery is aborted by a call to stop().

[signal] void QBluetoothDeviceDiscoveryAgent::deviceDiscovered(const QBluetoothDeviceInfo &info)

This signal is emitted when the Bluetooth device described by info is discovered.

The signal is emitted as soon as the most important device information has been collected. However, as long as the finished() signal has not been emitted the information collection continues even for already discovered devices. This is particularly true for signal strength information (RSSI). If signal strength information is required it is advisable to retrieve the device information via discoveredDevices() once the discovery has finished. This will yield the most recent RSSI information.

If lowEnergyDiscoveryTimeout() is larger than 0 the signal is only ever emitted when at least one attribute of info changes. This reflects the desire to receive updates as more precise information becomes available. The exception to this behavior is the case when lowEnergyDiscoveryTimeout is set to 0. A timeout of 0 expresses the desire to monitor the appearance and disappearance of Low Energy devices over time. Under this condition the deviceDiscovered() signal is emitted even if info has not changed since the last signal emission.

See also QBluetoothDeviceInfo::rssi() and lowEnergyDiscoveryTimeout().

QList<QBluetoothDeviceInfo> QBluetoothDeviceDiscoveryAgent::discoveredDevices() const

Returns a list of all discovered Bluetooth devices.

QBluetoothDeviceDiscoveryAgent::Error QBluetoothDeviceDiscoveryAgent::error() const

Returns the last error.

[signal] void QBluetoothDeviceDiscoveryAgent::error(QBluetoothDeviceDiscoveryAgent::Error error)

This signal is emitted when an error occurs during Bluetooth device discovery. The error parameter describes the error that occurred.

Note: Signal error is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

connect(bluetoothDeviceDiscoveryAgent, QOverload<QBluetoothDeviceDiscoveryAgent::Error>::of(&QBluetoothDeviceDiscoveryAgent::error),
    [=](QBluetoothDeviceDiscoveryAgent::Error error){ /* ... */ });

See also error() and errorString().

QString QBluetoothDeviceDiscoveryAgent::errorString() const

Returns a human-readable description of the last error.

[signal] void QBluetoothDeviceDiscoveryAgent::finished()

This signal is emitted when Bluetooth device discovery completes. The signal is not going to be emitted if the device discovery finishes with an error.

bool QBluetoothDeviceDiscoveryAgent::isActive() const

Returns true if the agent is currently discovering Bluetooth devices, otherwise returns false.

int QBluetoothDeviceDiscoveryAgent::lowEnergyDiscoveryTimeout() const

Returns a timeout in milliseconds that is applied to the Bluetooth Low Energy device search. A value of -1 implies that the platform does not support this property and the timeout for the device search cannot be adjusted. A return value of 0 implies a never-ending search which must be manually stopped via stop().

This function was introduced in Qt 5.8.

See also setLowEnergyDiscoveryTimeout().

void QBluetoothDeviceDiscoveryAgent::setLowEnergyDiscoveryTimeout(int timeout)

Sets the maximum search time for Bluetooth Low Energy device search to timeout in milliseconds. If timeout is 0 the discovery runs until stop() is called.

This reflects the fact that the discovery process for Bluetooth Low Energy devices is mostly open ended. The platform continues to look for more devices until the search is manually stopped. The timeout ensures that the search is aborted after timeout milliseconds. Of course, it is still possible to manually abort the discovery by calling stop().

The new timeout value does not take effect until the device search is restarted. In addition the timeout does not affect the classic Bluetooth device search. Depending on the platform the classic search may add more time to the total discovery process beyond timeout.

This function was introduced in Qt 5.8.

See also lowEnergyDiscoveryTimeout().

[slot] void QBluetoothDeviceDiscoveryAgent::start()

Starts Bluetooth device discovery, if it is not already started.

The deviceDiscovered() signal is emitted as each device is discovered. The finished() signal is emitted once device discovery is complete. The discovery utilizes the maximum set of supported discovery methods on the platform.

See also supportedDiscoveryMethods().

[slot] void QBluetoothDeviceDiscoveryAgent::start(QBluetoothDeviceDiscoveryAgent::DiscoveryMethods methods)

Starts Bluetooth device discovery, if it is not already started and the provided methods are supported. The discovery methods limit the scope of the device search. For example, if the target service or device is a Bluetooth Low Energy device, this function could be used to limit the search to Bluetooth Low Energy devices and thereby reduces the discovery time significantly.

Note: methods only determines the type of discovery and does not imply the filtering of the results. For example, the search may still contain classic bluetooth devices despite methods being set to LowEnergyMethod only. This may happen due to previously cached search results which may be incorporated into the search results.

This function was introduced in Qt 5.8.

[slot] void QBluetoothDeviceDiscoveryAgent::stop()

Stops Bluetooth device discovery. The cancel() signal is emitted once the device discovery is canceled. start() maybe called before the cancel signal is received. Once start() has been called the cancel signal from the prior discovery will be discarded.

[static] QBluetoothDeviceDiscoveryAgent::DiscoveryMethods QBluetoothDeviceDiscoveryAgent::supportedDiscoveryMethods()

This function returns the discovery methods supported by the current platform. It can be used to limit the scope of the device discovery.

This function was introduced in Qt 5.8.