Signal/Slot not working

VincentLiu

The flow of my code: Code flow <---- picture link

Hi, I have an signal/slot pair that doesn't work as expected. Can anyone help me ?

There are three classes: InspectionHandler, CommandProcess and SerialPortCtrl

The class InspectionHandler and SerialPortCtrl are declared in main.cpp as followed:

SerialPortCtrl *serialPortCtrl = new SerialPortCtrl;
InspectionHandler *inspectionHandler = new InspectionHandler(0);

QObject::connect(serialPortCtrl, &SerialPortCtrl::sendResponseSignal, inspectionHandler, &InspectionHandler::receiveResponseSlot);
QObject::connect(inspectionHandler, &InspectionHandler::sendRequestSignal, serialPortCtrl, &SerialPortCtrl::receiveRequestSlot);

And I declare the CommandProcess instance in the InspectionHandler constructor:

_commandProcessThread = new QThread();
_commandProcess = new CommandProcess();
_commandProcess->moveToThread(_commandProcessThread);

QObject::connect(_commandProcess, SIGNAL(initCompletedSignal()), _commandProcessThread, SLOT(start()));
QObject::connect(_commandProcessThread, SIGNAL(started()), _commandProcess, SLOT(processSlot()));
QObject::connect(_commandProcess, &CommandProcess::sendRequestSignal, this, &InspectionHandler::receiveRequest);

// ========= isConnected : true, but the connection does not really work ====================
bool isConnected = static_cast<bool>(QObject::connect(this, &InspectionHandler::sendResponse, _commandProcess, &CommandProcess::receiveResponseSlot), Qt::DirectConnection);

    // QObject::connect(_commandProcess, &CommandProcess::finishProcessSignal, _commandProcessThread, &QThread::quit);
    // QObject::connect(_commandProcessThread, &QThread::finished, _commandProcess, &CommandProcess::deleteLater);
    // QObject::connect(_commandProcessThread, &QThread::finished, _commandProcessThread, &QThread::deleteLater);

Several questions need your suggestion:

The isConnected is true. However, the CommandProcess::receiveResponseSlot doesn't receive the signal from &InspectionHandler::sendResponse, do I make any mistake? The error could be resulted from multiThreading design ?
Compare to the CommandProcess instance declared in InspectionHandler, I hope the control of serialport could be unique (as it is physically unique), so declare it as SerialPortCtrl *serialPortCtrl = new SerialPortCtrl in the main.cpp. Is it a good idea?

Thanks.

SGaist

Hi,

Can you show the signal and slot signatures ?

By the way, why are you static casting your connect call ? QObject::connect already returns a bool.

hskoglund

Hi, also about that Qt::DirectConnection, make sure it's not included in your connect() call, because it doesn't work across threads (you need to use Qt::AutoConnection or Qt::QueuedConnection)