QBluetoothDeviceDiscoveryAgent Class

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

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

Public Types

enum Error { NoError, PoweredOffError, InputOutputError, InvalidBluetoothAdapterError, UnsupportedPlatformError, UnknownError }
enum InquiryType { GeneralUnlimitedInquiry, LimitedInquiry }


  • inquiryType : QBluetoothDeviceDiscoveryAgent::InquiryType
  • 1 property inherited from QObject

Public Functions

QBluetoothDeviceDiscoveryAgent(QObject *parent = Q_NULLPTR)
QBluetoothDeviceDiscoveryAgent(const QBluetoothAddress &deviceAdapter, QObject *parent = Q_NULLPTR)
QList<QBluetoothDeviceInfo> discoveredDevices() const
Error error() const
QString errorString() const
QBluetoothDeviceDiscoveryAgent::InquiryType inquiryType() const
bool isActive() const
void setInquiryType(QBluetoothDeviceDiscoveryAgent::InquiryType type)
  • 31 public functions inherited from QObject

Public Slots

void start()
void stop()
  • 1 public slot inherited from QObject


void canceled()
void deviceDiscovered(const QBluetoothDeviceInfo &info)
void error(QBluetoothDeviceDiscoveryAgent::Error error)
void finished()

Additional Inherited Members

  • 11 static public members inherited from QObject
  • 9 protected functions inherited from QObject

Detailed Description

The QBluetoothDeviceDiscoveryAgent class discovers the Bluetooth devices nearby.

To discover the nearby Bluetooth devices:

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


// 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.

Note: Since Android 6.0 the ability to detect devices requires ACCESS_COARSE_LOCATION.

Member Type Documentation

enum QBluetoothDeviceDiscoveryAgent::Error

Indicates all possible error conditions found during Bluetooth device discovery.

QBluetoothDeviceDiscoveryAgent::NoError0No error has occurred.
QBluetoothDeviceDiscoveryAgent::PoweredOffError2The Bluetooth adaptor is powered off, power it on before doing discovery.
QBluetoothDeviceDiscoveryAgent::InputOutputError1Writing or reading from the device resulted in an error.
QBluetoothDeviceDiscoveryAgent::InvalidBluetoothAdapterError3The passed local adapter address does not match the physical adapter address of any local Bluetooth device.
QBluetoothDeviceDiscoveryAgent::UnsupportedPlatformError4Device 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::UnknownError100An unknown error has occurred.

enum QBluetoothDeviceDiscoveryAgent::InquiryType

This enum describes the inquiry type used while discovering Bluetooth devices.

QBluetoothDeviceDiscoveryAgent::GeneralUnlimitedInquiry0A general unlimited inquiry. Discovers all visible Bluetooth devices in the local vicinity.
QBluetoothDeviceDiscoveryAgent::LimitedInquiry1A limited inquiry discovers devices that are in limited inquiry mode.

LimitedInquiry is not supported on all platforms. If it is requested on a platform that does not support it, GeneralUnlimitedInquiry will be used instead. Setting LimitedInquiry is useful for multi-player Bluetooth-based games that needs faster communication between the devices. The phone scans for devices in LimitedInquiry and Service Discovery is done on one or two devices to speed up the service scan. After the game has connected to the device it intended to, the device returns to GeneralUnlimitedInquiry.

Property Documentation

inquiryType : QBluetoothDeviceDiscoveryAgent::InquiryType

This property holds type of inquiry scan to be used while discovering devices.

This property affects the type of inquiry scan which is performed while discovering devices.

By default, this property is set to GeneralUnlimitedInquiry.

Not all platforms support LimitedInquiry.

Access functions:

QBluetoothDeviceDiscoveryAgent::InquiryType inquiryType() const
void setInquiryType(QBluetoothDeviceDiscoveryAgent::InquiryType type)

See also InquiryType.

Member Function Documentation

QBluetoothDeviceDiscoveryAgent::QBluetoothDeviceDiscoveryAgent(QObject *parent = Q_NULLPTR)

Constructs a new Bluetooth device discovery agent with parent parent.

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


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.

See also QBluetoothDeviceInfo::rssi().

QList<QBluetoothDeviceInfo> QBluetoothDeviceDiscoveryAgent::discoveredDevices() const

Returns a list of all discovered Bluetooth devices.

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 one using the function pointer syntax, you must specify the signal type in a static cast, as shown in this example:

connect(bluetoothDeviceDiscoveryAgent, static_cast<void(QBluetoothDeviceDiscoveryAgent::*)(QBluetoothDeviceDiscoveryAgent::Error)>(&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.

[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.

[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.

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