API in C++ with Qt4 GUI

[pytro]

Hi all, i'm needing some big insights about an issue. Is it possible, to pass parameters on a C++ API to an Qt4 GUI project.
Basically is it possible to include classes from an API built in C++ VS2005 Project to a Qt4 GUI Project.

Regards,

Joseph.

[wysota]

Yes. Qt is just another library, it doesn't enforce any real limitations to your application.

[pytro]

Thanks for the help.

[pytro]

I'm working with a Network Enviroment API and there are many types of Threads.
In my console application, at "main".cpp i have this code:
...

xpto->start();
...
while (!xpto->hasTerminated()) {      
       //       update data.  
       //       and update network peers with new data.
    }
...

xpto->start();
...
while (!xpto->hasTerminated()) {      
       //       update data.  
       //       and update network peers with new data.
    }
...

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xpto is an object referenced to a class, that is derived from Thread.


The question is:
Is it possible to implement non-Qt API Threads, inside Qt-Gui main.cpp?
I want to update Qt-GUI widgets (i.e tableWidget items) with new data, every 20 sec.

I have looked for an answer and found this:
"Because of limitations inherited from the low-level libraries on which Qt's GUI support is built, QWidget and its subclasses are not reentrant. One consequence of this is that we cannot directly call functions on a widget from a secondary thread. If we want to, say, change the text of a QLabel from a secondary thread, we can emit a signal connected to QLabel::setText() or call QMetaObject::invokeMethod() from that thread."

What is the best way to do this?

Regards,

Joseph.

[wysota]

You can always post events to objects living in the gui thread as QCoreApplication::postEvent() is thread-safe. Then you can implement a handler that updates the gui from within the gui thread.

[pytro]

Hi again,
PostEvent is working perfectly with CustomEvent.
The problem is the while cycle that freezes Qt app.
What is the best way to solve this? QThread?

Thanks.

[wysota]

What is the best way to solve this? QThread?

No. Timers with 0ms timeout and implementing the functionality in a slot. Alternatively you might call qApp->processEvents() in that loop so that events are processed even if the loop blocks the flow.

[pytro]

Big Thanks again works like a charm

[pytro]

Hello again ,
I want acess updated data from xpto Class/Thread.

int main(int argc, char *argv[])
{	
QApplication a(argc, argv);
QtInterface w;	
Test *xpto;
....
QTimer *timer = new QTimer(&a);
a.connect(timer, SIGNAL(timeout()), &a, SLOT(w.dostuff(xpto)));	
timer->start(5000);
....
}

int main(int argc, char *argv[])
{	
QApplication a(argc, argv);
QtInterface w;	
Test *xpto;
....
QTimer *timer = new QTimer(&a);
a.connect(timer, SIGNAL(timeout()), &a, SLOT(w.dostuff(xpto)));	
timer->start(5000);
....
}

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Is this supose to call the SLOT in Qt.cpp every 5 sec., passing updated xpto?
Because i tested with timers in Qt.cpp and is working perfectly.
In Main.cpp isn't working.

Do i have to use a timer in Main.cpp and use another timer in Qt.cpp to update QTableWidgetItem?
How should i config both timers? (if needed)

Thanks.

[pytro]

Found the reason:

To start an event loop from a non-GUI thread, use QThread::exec()..

I think...