QLowEnergyCharacteristic Class

Member Function Documentation

QLowEnergyCharacteristic::QLowEnergyCharacteristic(const QLowEnergyCharacteristic &other)

Construct a new QLowEnergyCharacteristic that is a copy of other.

The two copies continue to share the same underlying data which does not detach upon write.

QLowEnergyCharacteristic::QLowEnergyCharacteristic()

Construct a new QLowEnergyCharacteristic. A default-constructed instance of this class is always invalid.

See also isValid().

QLowEnergyCharacteristic &QLowEnergyCharacteristic::operator=(const QLowEnergyCharacteristic &other)

Makes a copy of other and assigns it to this QLowEnergyCharacteristic object. The two copies continue to share the same service and controller details.

QLowEnergyCharacteristic::~QLowEnergyCharacteristic()

Destroys the QLowEnergyCharacteristic object.

[since 6.2] QLowEnergyDescriptor QLowEnergyCharacteristic::clientCharacteristicConfiguration() const

Returns the Client Characteristic Configuration Descriptor or an invalid QLowEnergyDescriptor instance if no Client Characteristic Configuration Descriptor exists.

BTLE characteristics can support notifications and/or indications. In both cases, the peripheral will inform the central on each change of the characteristic's value. In the BTLE attribute protocol, notification messages are not confirmed by the central, while indications are confirmed. Notifications are considered faster, but unreliable, while indications are slower and more reliable.

If a characteristic supports notification or indication, these can be enabled by writing special bit patterns to the Client Characteristic Configuration Descriptor. For convenience, these bit patterns are provided as QLowEnergyCharacteristic::CCCDDisable, QLowEnergyCharacteristic::CCCDEnableNotification, and QLowEnergyCharacteristic::CCCDEnableIndication.

Enabling e.g. notification for a characteristic named mycharacteristic in a service called myservice could be done using the following code.

 auto cccd = mycharacteristic.clientCharacteristicConfiguration();
 if (!cccd.isValid()) {
     // your error handling
     return error;
 }
 myservice->writeDescriptor(cccd, QLowEnergyCharacteristic::CCCDEnableNotification);

Note: Calling characteristic.clientCharacteristicConfiguration() is equivalent to calling characteristic.descriptor(QBluetoothUuid::DescriptorType::ClientCharacteristicConfiguration).

This function was introduced in Qt 6.2.

See also descriptor().

QLowEnergyDescriptor QLowEnergyCharacteristic::descriptor(const QBluetoothUuid &uuid) const

Returns the descriptor for uuid or an invalid QLowEnergyDescriptor instance.

See also descriptors().

QList<QLowEnergyDescriptor> QLowEnergyCharacteristic::descriptors() const

Returns the list of descriptors belonging to this characteristic; otherwise an empty list.

See also descriptor().

bool QLowEnergyCharacteristic::isValid() const

Returns true if the QLowEnergyCharacteristic object is valid, otherwise returns false.

An invalid characteristic object is not associated with any service (default-constructed) or the associated service is no longer valid due to a disconnect from the underlying Bluetooth Low Energy device, for example. Once the object is invalid it cannot become valid anymore.

Note: If a QLowEnergyCharacteristic instance turns invalid due to a disconnect from the underlying device, the information encapsulated by the current instance remains as it was at the time of the disconnect. Therefore it can be retrieved after the disconnect event.

QString QLowEnergyCharacteristic::name() const

Returns the human-readable name of the characteristic.

The name is based on the characteristic's uuid() which must have been standardized. The complete list of characteristic types can be found under Bluetooth.org Characteristics.

The returned string is empty if the uuid() is unknown.

See also QBluetoothUuid::characteristicToString().

QLowEnergyCharacteristic::PropertyTypes QLowEnergyCharacteristic::properties() const

Returns the properties of the characteristic.

The properties define the access permissions for the characteristic.

QBluetoothUuid QLowEnergyCharacteristic::uuid() const

Returns the UUID of the characteristic if isValid() returns true; otherwise a null UUID.

QByteArray QLowEnergyCharacteristic::value() const

Returns the cached value of the characteristic.

If the characteristic's properties() permit writing of new values, the value can be updated using QLowEnergyService::writeCharacteristic().

The cache is updated during the associated service's detail discovery, a successful read/write operation or when an update notification is received.

The returned QByteArray always remains empty if the characteristic does not have the read permission. In such cases only the QLowEnergyService::characteristicChanged() or QLowEnergyService::characteristicWritten() may provice information about the value of this characteristic.