I have a background thread and the thread calls some methods that update the UI (in order to show progress bars and show additional info in text areas).

If I modify some UI widget values, a "Cannot send events to objects owned by a different thread" assertion error is raised.

Looking at forums, I read that I could use QMetaObject::invokeMethod method but it just works if I pass it the Qt::DirectConnection flag that actually raises the same error shown above.

If I use Qt::QueuedConnection or Qt::AutoConnection, the invokeMethod returns false.

My code looks similar to this:

.h:

class A : public QMainWindow
{
  Q_OBJECT

  QProgressBar* pb;

  public slots:
    bool m(bool, int);
};

class B
{
  A* a;

  public:
    void handleEvent();
};


.cpp:

bool A::m(bool x, int y)
{
  pb->setValue(y);
  return x;
}

void B::handleEvent()
{
  //a->m(true, 12); //raises an assertion error

  bool r;
  //bool ret = QMetaObject::invokeMethod(a, "m", Qt::DirectConnection, Q_RETURN_ARG(bool, r), Q_ARG(bool, true), Q_ARG(int, 12)); //raises the same assertion error error

  bool ret = QMetaObject::invokeMethod(a, "m", Qt::AutoConnection, Q_RETURN_ARG(bool, r), Q_ARG(bool, true), Q_ARG(int, 12)); //is ignored and ret contains false.
}

Do you know what is going on or what i am doing wrong? or maybe, can someone suggest me another approach to deal with my newbie problem?

Thanks in advance,

Ernesto

c++ qt4
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