Cannot convert Qt4 Signal and slot to Qt5 Syntax
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Hello! Ealier I have the following signal and slot connect in my project, with Qt4 Syntax. And it runs well for a long time. ( CameraBus::getInstance() is the instance of a singleton, and getMainFrameObserverObj() returns a shared pointer of its member who is a instance of MainCameraFrameObserver. )
QObject::connect(CameraBus::getInstance().getMainFrameObserverObj(), SIGNAL(createdNewImg(cv::Mat)), this,SLOT(repaintImage(cv::Mat)));Now I want to write it in the Qt5 Syntax, since my project is using more and more Qt5 functions and features, so I change the code to this:
QObject::connect(CameraBus::getInstance().getMainFrameObserverObj(), &MainCameraFrameObserver::createdNewImg, this,&QmlImagePainter::repaintImage);However, I got the following two errors. I haven't understand everything of the Qt5 signal and slot, just changed the syntax but nothing else, anyone has idea about this?
error: invalid conversion from ‘QObject*’ to ‘const Object* {aka const MainCameraFrameObserver*}’ [-fpermissive]
QObject::connect(CameraBus::getInstance().getMainFrameObserverObj(),
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~error: no matching function for call to ‘QmlImagePainter::connect(QObject*, void (MainCameraFrameObserver::)(cv::Mat), QmlImagePainter, void (QmlImagePainter::*)(cv::Mat))’
this,&QmlImagePainter::repaintImage);
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Hi,
What is the signature of your getter function ?
Do you have overloads for your slot ?
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Hi thanks for the reply.
The getMainFrameObserverObj() function is of type QObject* , it's a shared pointer of the sender. The slot has no overloads.
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In that case shouldn't your rather have something like:
MainCameraFrameObserver *observer = qobject_cast<MainCameraFrameObserver *>CameraBus::getInstance().getMainFrameObserverObj(); QObject::connect(observer, &MainCameraFrameObserver::createdNewImg, this, &QmlImagePainter::repaintImage);And only then the connection statement ?
On a side note, it seems a bit strange that QmlImagePainter needs to know about your singleton and the MainCameraFrameObserver. This makes a tight coupling that will likely bring problems of maintenance in the long run.
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In that case shouldn't your rather have something like:
MainCameraFrameObserver *observer = qobject_cast<MainCameraFrameObserver *>CameraBus::getInstance().getMainFrameObserverObj(); QObject::connect(observer, &MainCameraFrameObserver::createdNewImg, this, &QmlImagePainter::repaintImage);And only then the connection statement ?
On a side note, it seems a bit strange that QmlImagePainter needs to know about your singleton and the MainCameraFrameObserver. This makes a tight coupling that will likely bring problems of maintenance in the long run.
@SGaist Thanks a lot! I see, compared with the earlier syntax with SIGNAL() and SLOT(), the sender in the connect cannot simply be a QObject* anymore. I'll fix it.
Also thanks for your note, my idea is that, I have a singleton named CameraBus, it emits images continously. And different other classes will be notified and then run their different slots(image displaying, processing... etc). So I connect the singleton's image signal with different slots in different classes.
I'm not experienced in large projects. Could you please give me a few hints about how to do it correctly? Thank you very much!
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The problem with your approach is that the classes that might be interested with the update have to know about your singleton, it should rather be done on a higher level e.g. the class that will manage the lifetime of QmlImagePainter.
