Den 27-02-2016 kl. 07:15 skrev Syam:
Hello,
Inspired from the recent discussions on QThread, I have the following
question.
I have:
class MyThread : public QThread
{
Q_OBJECT
//the constructor and other stuff
signals:
void mySignal();
protected:
virtual void run()
{
while(true)
{
//do something
if(some_condition) emit mySignal();
}
}
};
void MainWindow::someFunction()
{
MyThread *thread = new MyThread;
connect(thread, SIGNAL(mySignal()), this, SLOT(myGuiSlot()),
Qt::QueuedConnection);
thread->start();
}
//////////////////
Will the above code work fine? In myGuiSlot() I am typically
manipulating some widgets - setting the text of a QLabel etc.
Don't ever do this. I don't subscribe to the idea that you should never
subclass QThread yourself, but I think it's a very bad idea to subclass
and use signals and slots.
The reason is the discussion that followed in this thread - it's so hard
to understand precisely what happens with the connected signals and slots.
I usually tell people that QThread is a bridge between the creating and
the created thread. It's not actually, but conceptually it helps them to
realize that they should not assume they can understand the qobject
thread affinity inside the object itself.
If you use signals and slots in a thread object, you do this:
QThread* thread = new QThread;
MyObject* object = new MyObject;
object->moveToThread(thread);
thread->start();
If you don't and only do calculation, or use a queue or something to
handle the communication with hardware, etc, then you can subclass
QThread and do stuff in run(). (This part is where I disagree with the
"you're doing it wrong" crowd.) This is safe because without signals and
slots in there you don't use the thread affinity and you don't have a
local event loop.
Guys, this is only hard if you insist on doing something that
experienced people say you should stay away from. The OP thought the
MyObject should create it's own thread. No, that's wrong. Accept it and
move on. Or create a wrapper object around it if you must encapsulate it.
Bo Thorsen,
Director, Viking Software.
--
Viking Software
Qt and C++ developers for hire
http://www.vikingsoft.eu
_______________________________________________
Interest mailing list
[email protected]
http://lists.qt-project.org/mailman/listinfo/interest
