function 'connect' always look super class for slots.

[Intaek Lim]

Hello, I'm a newbie to qt programming.
These days, I write a simple image viewer with qt4 on WinXP. My code mainly consists of MyWindow derived from QMainWindow, MyImageWidget derived from QWidget.

Creating objects and showing images are all good but there's a problem with SIGNAL-SLOT connection.

Menus and actions are made in MyWindow::createMenu() before that is shown.


QMenu *fileMenu = menuBar()->addMenu("File");
openAction = fileMenu->addAction("Open");
connect(openAction, SIGNAL(triggered()), this, SLOT(fileOpen()));
return true;


Of course, openAction is a member variable of MyWindow and fileOpen() is a member function of the same class.

When I run the compiled binary, everything seem to be good, but the menu does not work and there's a error message in console window like this:

"Object::connect: No such slot QMainWindow::fileOpen()""

In my opinion, Object::connect function tries to find 'fileOpen' function in QMainWindow. But that is defined in the child class!!

I took some alternatives but I could not find any solution.


Thanks in advance.


Intaek.

[jpn]

Hi, add Q_OBJECT (http://doc.trolltech.com/4.2/qobject.html#Q_OBJECT) macro to the declaration of the class and re-run qmake to re-generate required steps for moc in the makefile.

[Intaek Lim]

Thanks, but I tried that. But when I add that macro, there are some link errors. What library should I add?



error LNK2001: "public: virtual struct QMetaObject const * __thiscall TVMainWindow::metaObject(void)const " (?metaObject@TVMainWindow@@UBEPBUQMetaObject@@XZ) tvmainwindow.obj
error LNK2001: "public: virtual void * __thiscall TVMainWindow::qt_metacast(char const *)" (?qt_metacast@TVMainWindow@@UAEPAXPBD@Z) tvmainwindow.obj
error LNK2001: "public: virtual int __thiscall TVMainWindow::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@TVMainWindow@@UAEHW4Call@QMetaObject @@HPAPAX@Z) 외부 기호를 tvmainwindow.obj

[jpn]

But when I add that macro, there are some link errors. What library should I add?
That's why I suggested re-running qmake. The required moc steps are missing. For signals and slots, an auto-generated piece of code must be compiled and linked. Adding the Q_OBJECT macro and re-running qmake takes care of this.

But, I see you are using Visual Studio. Do you have a commercial license and the Visual Studio integration? I think the commercial integration should take care of detecting an added Q_OBJECT macro automatically, but if you are using an open source version and the community patches, you might need to regenerate the Visual Studio project file or something.

[Intaek Lim]

Thank for your reply, but I don't know to qmake in WinXP environ. with VS2005.

[vermarajeev]

Thank for your reply, but I don't know to qmake in WinXP environ. with VS2005.

Create a seperate *.h and *.cpp file. Put your declarations in *.h and definations in *.cpp. Use Q_OBJECT macro defore defining your constructor in *.h file and before public specifier. Hit the "moc" button provided with vs-integration(which you can see at top after you have installed qt properly).

This should solve the problem.

[macbeth]

I'm not really sure, if I know what the problem exactly is, but some suggestions:

You should put Q_OBJECT macro inside your class and re-run qmake, but one other question crossed my mind: Did you put your function in 'public/private slots' section of the class?

[Antony]

if your MyWindow has more than one parent make sure that QMainWindow listed first:

class MyWindow: public QMainWindow,public AnyOtherParents

otherwise moc will parse it incorrectly.