Qt Bluetooth Module

Getting Started

As shown in the above list, the Qt Bluetooth API has three main purposes. The first one is to obtain local and remote device information. The first steps in retrieving device information is to check if Bluetooth is available on the device and read the local device address and name. The QBluetoothLocalDevice is the one to provide all of this information. Additionally you can use it to turn Bluetooth on and off and set the visibility on the device.

 QBluetoothLocalDevice localDevice;
 QString localDeviceName;

 // Check if Bluetooth is available on this device
 if (localDevice.isValid()) {

     // Turn Bluetooth on
     localDevice.powerOn();

     // Read local device name
     localDeviceName = localDevice.name();

     // Make it visible to others
     localDevice.setHostMode(QBluetoothLocalDevice::HostDiscoverable)
 }

Similar to the QBluetoothLocalDevice, the API offers QBluetoothDeviceInfo which provides that information for remote devices. While you can just create QBluetoothDeviceInfo objects on your own and fill them with data, the easier way is to use the QBluetoothDeviceDiscoveryAgent to start an automated search for visible Bluetooth devices within the connectable range.

 // Create a discovery agent and connect to its signals
 QBluetoothDiscoveryAgent *discoveryAgent = new QBluetoothDiscoveryAgent(this);
 connect(discoveryAgent, SIGNAL(deviceDiscovered(const QBluetoothDeviceInfo&)),
         this, SLOT(deviceDiscovered(const 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() << ')';
 }

Once the desired device is found, there are two main use cases provided by Qt Bluetooth. The simpler is to send files via the Obex Object Push Profile (OPP). As the name describes, this profile can only push files from one device to another but not pull files or browse the remote file system. Because of this limitation, this profile does not require the two devices to be paired before exchanging data. To push files to remote devices, create a QBluetoothTransferRequest and ask the QBluetoothTransferManager to push the file contained in the request by calling the put() function.

 // Create a transfer manager
 QBluetoothTransferManager *transferManager = new QBluetoothTransferManager(this);

 // Create the transfer request and file to be sent
 QBluetoothTransferRequest request(device.address());
 QFile *file = new QFile("testfile.txt");

 // Ask the transfer manager to send it
 QBluetoothTransferReply *reply = transferManager->put(request, file);

 // Connect to the reply's signals to be informed about the status and do cleanups when done
 connect(reply, SIGNAL(finished(QBluetoothTransferReply*)),
         this, SLOT(transferFinished(QBluetoothTransferReply*)));

The more flexible approach to do communication between two Bluetooth enabled devices, is to create a virtual serial port connection and freely exchange data over that connection. This can be done by the Serial Port Profile (SPP). The Serial Port Profile emulates a serial connection over the Bluetooth transport protocol RFCOMM.

To be able to create SPP connections, you need to register a Server one one device by using QRfcommServer.

 rfcommServer = new QRfcommServer(this);
 connect(rfcommServer, SIGNAL(newConnection()), this, SLOT(clientConnected()));
 rfcommServer->listen();

Connect to this server from another device playing the client role by using a QBluetoothSocket.

 void ChatClient::startClient(const QBluetoothServiceInfo &remoteService)
 {
     if (socket)
         return;

     // Connect to service
     socket = new QBluetoothSocket(QBluetoothSocket::RfcommSocket);
     qDebug() << "Create socket";
     socket->connectToService(remoteService);
     qDebug() << "ConnecttoService done";

     connect(socket, SIGNAL(readyRead()), this, SLOT(readSocket()));
     connect(socket, SIGNAL(connected()), this, SLOT(connected()));
     connect(socket, SIGNAL(disconnected()), this, SIGNAL(disconnected()));
 }

Using such a connection allows to exchange any form of data in both directions. It is perfectly suited for use cases like gaming or syncing the state between two instances of an application on two devices. For more detailed descriptions on how to configure the server and client, please refer to the detailed description sections in the QRfcommServer and QBluetoothSocket classes. A good example to start with SPP is the Bluetooth Chat example.

To get started with adding the Qt Bluetooth API to your project, see the Examples or check out the QML and C++ API's with their "Getting started" sections.