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Thread: signals are not working from QThread derived class

  1. #1
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    Default signals are not working from QThread derived class

    Hi all,

    Application couldn't receive signal from QThread object.

    I have implemented this way:

    workerthread.h:
    ----------------------
    Qt Code:
    1. #ifndef WORKERTHREAD_H
    2. #define WORKERTHREAD_H
    3.  
    4. #include <QThread>
    5.  
    6. class workerthread : public QThread
    7. {
    8. Q_OBJECT
    9. public:
    10. explicit workerthread(QObject *parent = 0);
    11. void run();
    12.  
    13. signals:
    14. void signal_worker_thread();
    15. };
    16.  
    17. #endif // WORKERTHREAD_H
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    workerthread.cpp
    -------------------------
    Qt Code:
    1. #include "workerthread.h"
    2. #include <QDebug>
    3.  
    4. workerthread::workerthread(QObject *parent) :
    5. QThread(parent)
    6. {
    7. }
    8.  
    9. void workerthread::run()
    10. {
    11. for(int i = 0; i < 10; ++ i)
    12. {
    13. qDebug() << "workerthread::signal_worker_thread()";
    14. emit signal_worker_thread();
    15. }
    16. return;
    17. }
    To copy to clipboard, switch view to plain text mode 

    WorkerThread is derived from QThread and overridden Run() method.
    I have launched this thread on GUI - button click event to do background process.

    Button click slot event:
    ---------------------------------
    Qt Code:
    1. void ProductNameDialog::slotButtonClicked()//
    2. {
    3. workerthread *pthread = new workerthread();
    4. QObject::connect(pthread, SIGNAL(signal_worker_thread()), this, SLOT(slotTest()));
    5.  
    6. pthread->start();
    7. pthread->wait();
    8.  
    9. accept();
    10. return;
    11. }
    To copy to clipboard, switch view to plain text mode 


    I have tested with sample Qt-GUI MainWindow application. It's working fine.

    When I integrated into my application, slotTest() is not fired. I hope, I am missing something. Can somebody suggest me what I am missing here.

    Thanks in advance.
    Last edited by high_flyer; 16th September 2013 at 11:56. Reason: code tags

  2. #2
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    Default Re: signals are not working from QThread derived class

    the problem is that you call QThread::wait()
    That will block the caller thread, in your case your GUI thread. While it is blocked it can't do anything, so it cannot process the signal event it is getting.

    Potential solution (depending in your problem)
    do not call wait, connect thread's finished() signal to dialog's accept() slot before calling thread's start method.

    Cheers,
    _

  3. #3
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    Default Re: signals are not working from QThread derived class

    in addition to what anda_skoa said, having the calling thread wait for your thread to end by blocking it, makes having the thread redundant.
    ==========================signature=============== ==================
    S.O.L.I.D principles (use them!):
    https://en.wikipedia.org/wiki/SOLID_...iented_design)

    Do you write clean code? - if you are TDD'ing then maybe, if not, your not writing clean code.

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