Connect signals with parameters to lambda functions

beecksche

Hi,
i connect some singals to a lambda function/slot. Can i also use the parameter of the signal in the lambda functions?

My current code:

if (mbServer->state() != QModbusDevice::UnconnectedState)
{
	mbServer->disconnectDevice();

	QEventLoop loop;
	connect(mbServer, &QModbusDevice::stateChanged, this, [this, &loop]
	{
		if (mbServer->state() == QModbusDevice::UnconnectedState)
			loop.quit();
	});

	loop.exec();
}

The signal QModbusDevice::stateChange has the parameter QModbusDevice::State state (http://doc.qt.io/qt-5/qmodbusdevice.html#stateChanged).

Thanks!

kshegunov

@beecksche

Can i also use the paramater of the signals in the lambda functions?

You can, but your lambda should have parameters as well ... :)

QEventLoop loop;

auto lambda = [&loop] (QModbusDevice::State state) -> void
{
    if (state == QModbusDevice::UnconnectedState)
        loop.quit();
}

connect(mbServer, &QModbusDevice::stateChanged, lambda);

Kind regards.

beecksche

@kshegunov

Works perfectly, thanks a lot!

kshegunov

@beecksche
No problem. May I ask something? Is modbus communication synchronous, I didn't see any async API in the docs?

beecksche

@kshegunov
Modbus clients have a asynchronous API (http://doc.qt.io/qt-5/qmodbusclient.html#details).

For modbus servers it is not specified in the docs. But as far as i used the class, all calls are also asynchronous. In my case i want to ensure that server is not connected, before connect again. If i understood the docs of the QModbusDevice correctly, it is also possible to inherit from QModbusDevice and override the open() and close() function to ensure that.

kshegunov

@beecksche said:

Modbus clients have a asynchronous API

Thanks. I skipped the description and went directly to the signals, but the way the API is organized is a bit different from QTcpSocket, so I got tangled up ... :D

beecksche

@kshegunov said:

the way the API is organized is a bit different from QTcpSocket

You're right. I was also a little bit confused, when i used the QSerialBus module the first time (see my topic https://forum.qt.io/topic/65572/qmodbusmaster-example).

Like i said, i think you can built your own class by inherit from QModbusDevice to have a synchronous API. The QSerialBus module is marked as technical preview in Qt 5.6, maybe they add some new functions in future releases similar to QTcpSocket like waitForConnected etc.