Problem with Slots and Signals

Gnarg · 10-05-2005, 06:57 AM

Hi all,

I have read many tutorials on programming in KDE with QTDesigner. When I write small apps to learn, everything compiles and runs fine including any slots and signals I have. I wanted to learn a little more and understand more how slots and signals work so I decided to write a small learning app not using QTDeisgner and do it all manual.

My problem is I am writing an app with 2 buttons one with a Quit button and another with an Open button that calls a function openmyimage. From what I have been reading it looks like its fine but when I compile ( no warnings or errors ) and run the small learning app I keep getting a message in the Application tab in KDevelop:

QObject::connect: No such slot QApplication::openmyimage()
QObject::connect: (sender name: 'openbutton')
QObject::connect: (receiver name: 'chtest')

Then the application shows with two buttons.

This causes the Open button to do nothing when clicked. Right now all I wanted to do in the openmyimage function is to call a qwarning to display a message in the Application tab.

I need another pair of eyes to pinpoint my mistake. Can anyone please take a look at my code and let me know where I went wrong. Since this is just a learning app for me to learn Signals and Slots a little better I did everything in one file and compiled so copying this code and pasting it in your dev environment should work.

Code:

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <qapplication.h>
#include <qfont.h>
#include <qpushbutton.h>




class MyWidget : public QWidget
{
	//Q_OBJECT
public:

	MyWidget(QWidget *parent=0, const char *name=0);
	

public slots:
	void openmyimage();	

signals:
	void clicked();
};



MyWidget::MyWidget (QWidget *parent, const char *name) : QWidget(parent, name) 
{

	setMinimumSize (200,120);
	setMaximumSize (200,120);
  
  QPushButton *quit = new QPushButton("Quit", this, "quit");
  quit->setGeometry(10,10,75,30);
  quit->setFont( QFont("Times", 18, QFont::Bold));

  QPushButton *btnopen = new QPushButton("Open1", this, "openbutton");
  btnopen->setGeometry(10,45,75,30);
  btnopen->setFont( QFont("Times", 18, QFont::Bold));

  
   
  connect (quit,    SIGNAL(clicked()), qApp, SLOT(quit()) );
  connect (btnopen, SIGNAL(clicked()), qApp, SLOT(openmyimage()) );
  
  qWarning("Finished in Constructor");
}




void MyWidget::openmyimage()
{
 qWarning("test");
}






int main(int argc, char *argv[])
{
  QApplication a(argc, argv);

  MyWidget w;
  
  
  
  w.setGeometry (100,100,200,120);
  a.setMainWidget( &w);
  w.show();
  return a.exec();
}

I have alrady tried moving each class into its own .cpp and .h file with the same results. Changed the slot name,
Changed

Code:

connect (btnopen, SIGNAL(clicked()), qApp, SLOT(openmyimage()) );

to

Code:

connect (btnopen, SIGNAL(clicked()), this, SLOT(openmyimage()) );

When I add Q_OBJECT into the MyWidget class I get a compile error with just an exit status 2.

Thanks for taking the time to look.

Gnarg

paulsm4 · 10-06-2005, 03:15 PM

Uncomment the "Q_OBJECT" and try this:
http://www.qtforum.org/thread.php?postid=1329

'Hope that helps .. PSM

Gnarg · 10-07-2005, 07:19 AM

Hi paulsm4,

Thanks for your reply, I have removed the Q_OBJECT macro before and allows me to compile successfully but then I run into the whole connect issue I mentioned. I did find an alternative which works for me so I'll use that and learn from it.

All I did was create a QMAKE Application and removed all the code that was not needed like a toolbar, menu and status bar. What is left is a small framework with basically nothing. Then I added my buttons and connected the buttons to some slots and as I click on the buttons I get my qWarning as I expected.

There is a difference from the code I posted and what was created from the framework is my code uses QWidget where the framework used QMainWindow.

If you or anyone else knows what I did wrong I still would like to see where I went wrong.

Gnarg