QBluetoothDeviceDiscoveryAgent Class

The QBluetoothDeviceDiscoveryAgent class discovers the Bluetooth devices nearby. More...

Header:	#include <QBluetoothDeviceDiscoveryAgent>
qmake:	QT += bluetooth
Since:	Qt 5.2
Inherits:	QObject

• List of all members, including inherited members

Public Types

enum	DiscoveryMethod { NoMethod, ClassicMethod, LowEnergyMethod }
flags	DiscoveryMethods
enum	Error { NoError, PoweredOffError, InputOutputError, InvalidBluetoothAdapterError, UnsupportedPlatformError, …, UnknownError }

Public Functions

	QBluetoothDeviceDiscoveryAgent(const QBluetoothAddress &deviceAdapter, QObject *parent = nullptr)
	QBluetoothDeviceDiscoveryAgent(QObject *parent = nullptr)
virtual	~QBluetoothDeviceDiscoveryAgent()
QList<QBluetoothDeviceInfo>	discoveredDevices() const
QBluetoothDeviceDiscoveryAgent::Error	error() const
QString	errorString() const
bool	isActive() const
int	lowEnergyDiscoveryTimeout() const
void	setLowEnergyDiscoveryTimeout(int timeout)

Public Slots

void	start(QBluetoothDeviceDiscoveryAgent::DiscoveryMethods methods)
void	start()
void	stop()

Signals

void	canceled()
void	deviceDiscovered(const QBluetoothDeviceInfo &info)
void	deviceUpdated(const QBluetoothDeviceInfo &info, QBluetoothDeviceInfo::Fields updatedFields)
void	errorOccurred(QBluetoothDeviceDiscoveryAgent::Error error)
void	finished()

Static Public Members

QBluetoothDeviceDiscoveryAgent::DiscoveryMethods

supportedDiscoveryMethods()

Detailed Description

To discover the nearby Bluetooth devices:

• create an instance of QBluetoothDeviceDiscoveryAgent,
• connect to either the deviceDiscovered() or finished() signals,
• and call start().

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() << ')';
}

To retrieve results asynchronously, connect to the deviceDiscovered() signal. To get a list of all discovered devices, call discoveredDevices() after the finished() signal.

This class can be used to discover Classic and Low Energy Bluetooth devices. The individual device type can be determined via the QBluetoothDeviceInfo::coreConfigurations() attribute. In most cases the list returned by discoveredDevices() contains both types of devices. However not every platform can detect both types of devices. On platforms with this limitation (for example iOS only suports Low Energy discovery), the discovery process will limit the search to the type which is supported.

Member Type Documentation

[since 5.8] enum QBluetoothDeviceDiscoveryAgent::DiscoveryMethodflags QBluetoothDeviceDiscoveryAgent::DiscoveryMethods

This enum descibes the type of discovery method employed by the QBluetoothDeviceDiscoveryAgent.

Constant	Value	Description
QBluetoothDeviceDiscoveryAgent::NoMethod	0x0	The discovery is not possible. None of the available methods are supported.
QBluetoothDeviceDiscoveryAgent::ClassicMethod	0x01	The discovery process searches for Bluetooth Classic (BaseRate) devices.
QBluetoothDeviceDiscoveryAgent::LowEnergyMethod	0x02	The discovery process searches for Bluetooth Low Energy devices.

This enum was introduced or modified in Qt 5.8.

The DiscoveryMethods type is a typedef for QFlags<DiscoveryMethod>. It stores an OR combination of DiscoveryMethod values.

See also supportedDiscoveryMethods().

enum QBluetoothDeviceDiscoveryAgent::Error

Indicates all possible error conditions found during Bluetooth device discovery.

Constant	Value	Description
QBluetoothDeviceDiscoveryAgent::NoError	0	No error has occurred.
QBluetoothDeviceDiscoveryAgent::PoweredOffError	2	The Bluetooth adaptor is powered off, power it on before doing discovery.
QBluetoothDeviceDiscoveryAgent::InputOutputError	1	Writing or reading from the device resulted in an error.
QBluetoothDeviceDiscoveryAgent::InvalidBluetoothAdapterError	3	The passed local adapter address does not match the physical adapter address of any local Bluetooth device.
QBluetoothDeviceDiscoveryAgent::UnsupportedPlatformError	4	Device discovery is not possible or implemented on the current platform. The error is set in response to a call to start(). An example for such cases are iOS versions below 5.0 which do not support Bluetooth device search at all. This value was introduced by Qt 5.5.
QBluetoothDeviceDiscoveryAgent::UnsupportedDiscoveryMethod	5	One of the requested discovery methods is not supported by the current platform. This value was introduced by Qt 5.8.
QBluetoothDeviceDiscoveryAgent::LocationServiceTurnedOffError	6	The location service is turned off. Usage of Bluetooth APIs is not possible when location service is turned off. This value was introduced by Qt 6.2.
QBluetoothDeviceDiscoveryAgent::UnknownError	100	An unknown error has occurred.

Member Function Documentation

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().

QBluetoothDeviceDiscoveryAgent::QBluetoothDeviceDiscoveryAgent(QObject *parent = nullptr)

Constructs a new Bluetooth device discovery agent with parent parent.

[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) and manufacturer data updates. If the use case requires continuous manufacturer data or RSSI updates it is advisable to retrieve the device information via discoveredDevices() once the discovery has finished or listen to the deviceUpdated() signal.

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().

[signal] void QBluetoothDeviceDiscoveryAgent::deviceUpdated(const QBluetoothDeviceInfo &info, QBluetoothDeviceInfo::Fields updatedFields)

This signal is emitted when the agent receives additional information about the Bluetooth device described by info. The updatedFields flags tell which information has been updated.

During discovery, some information can change dynamically, such as signal strength and manufacturerData. This signal informs you that if your application is displaying this data, it can be updated, rather than waiting until the discovery has finished.

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

[signal, since 6.2] void QBluetoothDeviceDiscoveryAgent::errorOccurred(QBluetoothDeviceDiscoveryAgent::Error error)

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

This function was introduced in Qt 6.2.

See also error() and errorString().

[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.

[slot, since 5.8] 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.

This function was introduced in Qt 5.8.

[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::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.

[virtual] QBluetoothDeviceDiscoveryAgent::~QBluetoothDeviceDiscoveryAgent()

Destructor for ~QBluetoothDeviceDiscoveryAgent()

QList<QBluetoothDeviceInfo> QBluetoothDeviceDiscoveryAgent::discoveredDevices() const

Returns a list of all discovered Bluetooth devices.

QBluetoothDeviceDiscoveryAgent::Error QBluetoothDeviceDiscoveryAgent::error() const

Returns the last error.

QString QBluetoothDeviceDiscoveryAgent::errorString() const

Returns a human-readable description of the last error.

bool QBluetoothDeviceDiscoveryAgent::isActive() const

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

[since 5.8] 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().

[since 5.8] 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().

[static, since 5.8] 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.