Qt 5.6 | Qt Bluetooth | C++ Classes | QBluetoothDeviceDiscoveryAgent

Qt 5.6.2 Reference Documentation

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

## Properties

- inquiryType : QBluetoothDeviceDiscoveryAgent::InquiryType

- 1 property inherited from QObject

## Public Functions

| QBluetoothDeviceDiscoveryAgent(QObject *parent = Q_NULLPTR)
| QBluetoothDeviceDiscoveryAgent(const QBluetoothAddress &deviceAdapter, QObject *parent = Q_NULLPTR)
| ~QBluetoothDeviceDiscoveryAgent()
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

## Signals

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

- 2 signals inherited from QObject

### Additional Inherited Members

- 1 public variable inherited from QObject
- 10 static public members inherited from QObject
- 9 protected functions inherited from QObject
- 2 protected variables inherited from QObject

## Detailed Description

The QBluetoothDeviceDiscoveryAgent class discovers the Bluetooth devices nearby.

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.

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.

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::UnknownError` | `100` | An unknown error has occurred.

### enum QBluetoothDeviceDiscoveryAgent::InquiryType

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

Constant | Value | Description
--- | --- | ---
`QBluetoothDeviceDiscoveryAgent::GeneralUnlimitedInquiry` | `0` | A general unlimited inquiry. Discovers all visible Bluetooth devices in the local vicinity.
`QBluetoothDeviceDiscoveryAgent::LimitedInquiry` | `1` | A 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().

### 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.

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.