QtBluetooth - Linker Problems

[LaboratoryRat]

Hello everyone!

I'm a student in electical engineering, having some troubles with C++ / Qt Programming. For a students project, I've to program a simple app on Sailfish OS (Device: Jolla 1, QtBluetooth 5.2) which listens to UDP datagrams (that works well) and hands them over to a Bluetooth SPP connection (rfcomm protocol). It's mainly just a control software for a RGBW lamp, which gets connected via BT.

UDP and Bluetooth are in the same project, accessing the same include-space.
While my UDP connection works flawlessly, the Bluetooth code causes the linker to stop and hand out the error:

\home\mersdk\share\LightCubeServer\src\btconn.cpp: 14: Error: undefined reference to `QBluetoothServer::QBluetoothServer(QBluetoothServ iceInfo::Protocol, QObject*)'

After spending two weekends of reading documentations, I've no clue on what to do anymore. I even attached the corresponding include files to the project, which didn't change anything.

The Header file btconn.h:

#include <QtCore/QObject>
#include <QtBluetooth/QBluetoothServer>
 
QT_FORWARD_DECLARE_CLASS(QBluetoothServer)
 
class BtConn : public QObject
{
    Q_OBJECT
public:
    explicit BtConn(QObject *parent = 0);  // Constructor
    void startServer(const QBluetoothAddress &localAdapter = QBluetoothAddress()); // Method used for starting the server
private:
    QBluetoothServer *rfcommServer; // Variable for Server-Instance
};

#include <QtCore/QObject>
#include <QtBluetooth/QBluetoothServer>

QT_FORWARD_DECLARE_CLASS(QBluetoothServer)

class BtConn : public QObject
{
    Q_OBJECT
public:
    explicit BtConn(QObject *parent = 0);  // Constructor
    void startServer(const QBluetoothAddress &localAdapter = QBluetoothAddress()); // Method used for starting the server
private:
    QBluetoothServer *rfcommServer; // Variable for Server-Instance
};

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and the Code File btconn.cpp:

#include "btconn.h"
 
BtConn::BtConn(QObject *parent) : QObject(parent)
{
// Constructor won't do anything
}
 
// Start the Bluetooth Server
void BtConn::startServer(const QBluetoothAddress& localAdapter)
{
    if (rfcommServer)
        return;
 
    rfcommServer = new QBluetoothServer(QBluetoothServiceInfo::RfcommProtocol, this);
 
}

#include "btconn.h"

BtConn::BtConn(QObject *parent) : QObject(parent)
{
// Constructor won't do anything
}

// Start the Bluetooth Server
void BtConn::startServer(const QBluetoothAddress& localAdapter)
{
    if (rfcommServer)
        return;

    rfcommServer = new QBluetoothServer(QBluetoothServiceInfo::RfcommProtocol, this);

}

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I really hope that someone has an idea on how to solve that problem.

Best regards

PS: English isn't my main language - sorry for typos and grammar mistakes.