Qt Bluetooth - no devices discovered.

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 So, if this is your own class simply add a signal to it and connect it to &QBluetoothDeviceDiscoveryAgent::finished

I use this class from the example (lowenergyscanner).
I get an error - finished is a private member.

[jsulm]

@jenya7 https://doc.qt.io/qt-5/qbluetoothdevicediscoveryagent.html#finished - does not look like private to me.
Please post whole error message and code.

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 https://doc.qt.io/qt-5/qbluetoothdevicediscoveryagent.html#finished - does not look like private to me.
Please post whole error message and code.

QBluetoothDeviceDiscoveryAgent - it is global.

but in the class

private:
    QBluetoothDeviceDiscoveryAgent *discoveryAgent;

and in constructor

connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::deviceScanFinished);

Actually it's a pointer ( *discoveryAgent). How do I pass my object (QBluetoothDeviceDiscoveryAgent ) to the class?

[jsulm]

@jenya7 said in Qt Bluetooth - no devices discovered.:

Actually it's a pointer ( *discoveryAgent). How do I pass my object (QBluetoothDeviceDiscoveryAgent ) to the class?

You don't.
What I suggested is:

• Add a signal to Device class
• Connect discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished to this new signal
• Other classes can now connect to this new signal

No need to pass anything to anybody...

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 said in Qt Bluetooth - no devices discovered.:

Actually it's a pointer ( *discoveryAgent). How do I pass my object (QBluetoothDeviceDiscoveryAgent ) to the class?

You don't.
What I suggested is:

• Add a signal to Device class
• Connect discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished to this new signal
• Other classes can now connect to this new signal

No need to pass anything to anybody...

OK.

Device::Device()
{
    //! [les-devicediscovery-1]
    discoveryAgent = new QBluetoothDeviceDiscoveryAgent();
    discoveryAgent->setLowEnergyDiscoveryTimeout(5000);
    connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::deviceDiscovered,
            this, &Device::addDevice);
    connect(discoveryAgent, QOverload<QBluetoothDeviceDiscoveryAgent::Error>::of(&QBluetoothDeviceDiscoveryAgent::error),
            this, &Device::deviceScanError);
    connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::deviceScanFinished);
    //! [les-devicediscovery-1]

    setUpdate("Search");
}

a private  finished  connected to a private  deviceScanFinished. What's  the point in it?

[jsulm]

This post is deleted!

[jsulm]

@jenya7 Did you actually read what I wrote?!
For the third time: you add a new SIGNAL to Device class...

connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::scanFinished); // scanFinished is the new signal

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 And why is deviceScanFinished private?
It is actually apparent that it should be public...

it's an official example in the examples folder (C:\Qt\Examples\Qt-5.12.0\bluetooth\lowenergyscanner).
I wouldn't dare to change it, only if you say so.

[jsulm]

@jenya7 Please read my post above your last post...

[jenya7]

@jsulm
What if I do deviceScanFinished public?

OK. I see what's going on. Just a strong encapsulation.

The signal already set

connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::deviceScanFinished);

and it sets m_deviceScanState

void Device::deviceScanFinished()
{
    emit devicesUpdated();
    m_deviceScanState = false;
    emit stateChanged();
    if (devices.isEmpty())
        setUpdate("No Low Energy devices found...");
    else
        setUpdate("Done! Scan Again!");
}

so my

 while (bt_device.state()) ;

actually tests the memeber

bool Device::state()
{
    return m_deviceScanState;
}

so deviceScanFinished never occurs.

[jsulm]

@jenya7 said in Qt Bluetooth - no devices discovered.:

What if I do deviceScanFinished public?

To achieve what exactly? deviceScanFinished is a slot not signal in Device - how will making it public help other classes?

"The signal already set" - the signal from private member is "set", this does not help other classes as you already discovered.

Why don't you try my approach? Signals/slots are one of the most important features in Qt and it is really not much work:

class Device...
{
signals:
    void scanFinished();
}

// In Device constructor:
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::deviceScanFinished);
connect(discoveryAgent, &QBluetoothDeviceDiscoveryAgent::finished, this, &Device::scanFinished);

// Now in some other class you simply do:
connect(&bt_device, &Device::scanFinished, this, &SomeOtherClass::someSlot);

Isn't this easy and clear? And you do not expose any private members from Device to outer world (which would be bad design).

[jenya7]

@jsulm
It seems OK. But here in the constructor

BT_DEVICE::BT_DEVICE(QObject *parent) : QObject(parent)
{
    connect(&bt_device, &Device::scanFinished, this, &BT_DEVICE::ScanFinished);
}

I get - "undefined reference to `vtable for BT_DEVICE' ". And I don't have any virtual function.

[jsulm]

@jenya7 Please read https://doc.qt.io/qt-5/signalsandslots.html
If you want to have signals and/or slots in a class you have to derive this class from QObject and add Q_OBJECT macro right at the beginning of your class.

#include <QObject>

class BT_DEVICE : public QObject
{
Q_OBJECT

signals:
    void scanFinished();
...

Do a complete rebuild of your project after these changes.

[jenya7]

@jsulm
this is h file

class BT_DEVICE : public QObject
{
    Q_OBJECT

    public:
    BT_DEVICE(QObject *parent = nullptr);
    void BLE_Scan();

signals:
    void ScanFinished();
};

and cpp file

BT_DEVICE::BT_DEVICE(QObject *parent) : QObject(parent)
{
    connect(&bt_device, &Device::scanFinished, this, &BT_DEVICE::ScanFinished);
}

void BT_DEVICE::BLE_Scan()
{
   scanning = 1;

   bt_device.startDeviceDiscovery();

   while (scanning) ;

   QVariant devices = bt_device.getDevices();
}

void BT_DEVICE::ScanFinished()
{
    scanning = 0;
}

[jsulm]

@jenya7 said in Qt Bluetooth - no devices discovered.:

while (scanning) ;

Not related to your current problem: this is a no go in an event driven application! You are blocking the event loop! This means that no signals will be handled. Redesign this part of your app.

Back to your current problem: I did a mistake above. BT_DEVICE::ScanFinished should be a slot of course.

[jenya7]

@jsulm
yes. it was stupid of me to block. for now
h

class BT_DEVICE : public QObject
{
    Q_OBJECT

    public:
    BT_DEVICE(QObject *parent = nullptr);
    void BLE_Scan();

public slots:
    void ScanFinished();
};

cpp

BT_DEVICE::BT_DEVICE(QObject *parent) : QObject(parent)
{
    //for debug
    //connect(&bt_device, &Device::scanFinished, this, &BT_DEVICE::ScanFinished);
}

void BT_DEVICE::BLE_Scan()
{
   scanning = 1;

   bt_device.startDeviceDiscovery();
}

void BT_DEVICE::ScanFinished()
{
    QVariant devices = bt_device.getDevices();
}

Is it OK?

[jsulm]

@jenya7 said in Qt Bluetooth - no devices discovered.:

Is it OK?

Why did you comment out the connect?

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 said in Qt Bluetooth - no devices discovered.:

Is it OK?

Why did you comment out the connect?

for debug. I still get the error.
On Windows I get a different error - error: multiple definition of `Device::scanFinished()' in moc_device.cpp.
first defined here device.cpp.
I wonder how can it be - moc file is a generated file after build.

[jsulm]

@jenya7 said in Qt Bluetooth - no devices discovered.:

I wonder how can it be - moc file is a generated file after build

It is probably a remnant from previos version when scanFinished was declared as signal.
Do a complete rebuild: delete build folder, run qmake and build.

[jenya7]

@jsulm said in Qt Bluetooth - no devices discovered.:

@jenya7 said in Qt Bluetooth - no devices discovered.:

I wonder how can it be - moc file is a generated file after build

It is probably a remnant from previos version when scanFinished was declared as signal.
Do a complete rebuild: delete build folder, run qmake and build.

Deleted all from the build folder. Clean. Rebuild. I see new files created. The same problem.
Renamed scanFinished for scanCompleted. Still the same problem.