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Thread: Qt signals/slots dll for non-Qt app

  1. #1
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    Default Qt signals/slots dll for non-Qt app

    Hi All,

    I have a problem with the signal/slots for my dll.


    Here is my setup:

    1) MySystemWrapper.dll is a c wrapper that can be called from python (or other app.. but for now I use python to debug).
    The connect() function calls the Qt dll that cannot be called with other apps.

    Qt Code:
    1. bool connect(){
    2. QAppPriv::pApp = new QCoreApplication(QAppPriv::argc, QAppPriv::argv); //to handle signals and slots
    3. mSystem = new mySystem();
    4.  
    5. return true;
    6. }
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    2) In the mySystem.dll the constructor looks like this:

    Qt Code:
    1. MySystem::MySystem()
    2. {
    3.  
    4. QThread *thread = new QThread;
    5.  
    6. //USB HID interface
    7. plugNPlay = new HID_PnP();
    8. plugNPlay->moveToThread(thread);
    9. plugNPlay->start();
    10.  
    11.  
    12.  
    13. ////signal slots test
    14.  
    15. processEventsTmr = new QTimer(this);
    16. processEventsTmr->setInterval(1000); //x ms between each process events
    17. connect(processEventsTmr,SIGNAL(timeout()), this, SLOT(processMyEvents()));
    18.  
    19. }
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    The problem I have is that processMyEvents() is never called. So the signal/slot does not work in the MySystem object.

    HOWEVER, the signal/slot ARE WORKING in the plugNPlay object.

    I think my problem is with the way new QCoreApplication is called but I can figure it out.

    I have read this over and over again!

    Thanks

  2. #2
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    Default Re: Qt signals/slots dll for non-Qt app

    So where are you calling QCoreApplication::exec() on your application instance? If the event loop isn't running, events don't get processed. You also can't have more than one QCoreApplication instance, but your connect() method will create a new one every time it is called.

    I think you need to read the stackoverflow post at least one more time, and follow the suggestions exactly.

  3. The following user says thank you to d_stranz for this useful post:

    bareil76 (24th October 2014)

  4. #3
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    Default Re: Qt signals/slots dll for non-Qt app

    Ok..

    here is what I have now.

    What works:
    a) The plugNPlay object has timers and connects that work.
    b) connect(plugNPlay, SIGNAL(JustConnected(bool)),this,SLOT(initialize(b ool)), Qt::QueuedConnection); is also working
    c) connect(retryTmr,SIGNAL(timeout()), this, SLOT(handleNoResponse())); also works.

    What doesn't work:
    a) In the initialize(bool) slot.. I have retryTmr->start();... the system complains that:

    QObject::killTimer: timers cannot be stopped from another thread
    QObject::startTimer: timers cannot be started from another thread



    1) First MySystemWrapper which is called first. I had to put the MySystem object in another thread because if I don't.. nothing works!

    Qt Code:
    1. bool MYSYSTEMWRAPPERSHARED_EXPORT connect(){
    2.  
    3. mMySystem = new MySystem();
    4. mMySystem->moveToThread(thread2);
    5. thread2->start();
    6. QMetaObject::invokeMethod(mMySystem, "run", Qt::QueuedConnection);
    7.  
    8.  
    9. return true;
    10. }
    To copy to clipboard, switch view to plain text mode 

    2) Then, the MySystem class is called from the above. The constructor is only to start the QApp. With the signal that will call exec().... ONLY then I call the run() that will created my program objects.

    Qt Code:
    1. MySystem::MySystem(QObject *parent) :
    2. QObject(parent)
    3. {
    4. if (QAppPriv::pThread == NULL)
    5. {
    6. qDebug()<< "QAppPriv::pThread created";
    7. // Separate thread for application thread
    8. QAppPriv::pThread = new QThread();
    9. // Direct connection is mandatory
    10. QObject::connect(QAppPriv::pThread, SIGNAL(started()), this, SLOT(OnExec()), Qt::DirectConnection);
    11. QAppPriv::pThread->start();
    12. }
    13.  
    14.  
    15. }
    16. void MySystem::OnExec(){
    17. if (QCoreApplication::instance() == NULL)
    18. {
    19. qDebug()<< "QAppPriv::pApp created";
    20. QAppPriv::pApp = new QCoreApplication(QAppPriv::argc, QAppPriv::argv);
    21. QAppPriv::pApp->exec();
    22. if (QAppPriv::pApp)
    23. delete QAppPriv::pApp;
    24. }
    25. }
    26.  
    27.  
    28.  
    29. void MySystem::run(){
    30. QThread *thread = new QThread;
    31. plugNPlay = new HID_PnP();
    32. plugNPlay->moveToThread(thread);
    33.  
    34. isConnected = false;
    35.  
    36.  
    37.  
    38. retryTmr = new QTimer(this);
    39. retryTmr->setSingleShot(true);
    40. retryTmr->setInterval(10); //10ms between retry
    41. connect(retryTmr,SIGNAL(timeout()), this, SLOT(handleNoResponse()));
    42.  
    43.  
    44.  
    45. connect(plugNPlay, SIGNAL(JustConnected(bool)),this,SLOT(initialize(bool)),
    46. Qt::QueuedConnection);
    47. }
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  5. #4
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    Default Re: Qt signals/slots dll for non-Qt app

    The above worked... I had another problem. SOLVED

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