[Qt-interest] Runtime Error :- connect: No such slot ...

[Wm. G. Urquhart]

Sean Harmer wrote:
> Hi,
> 
> On Thursday 18 February 2010 20:47:07 Wm. G. Urquhart wrote:
>> Hi All,
>>
>> I have a class derived from QThread that contains some signals, but when
>> I try to connect these signals to the UI I get a runtime error telling
>> me that the SLOT to which I want to connect said signals to does not exist.
>>
>> In the UI header file I have
>>
>> private slots:
>> void loadComplete(size_t) ;
>>
>> and in the UI .cpp I have :
>>
>> void MyApp::loadComplete(size_t count)
>> {
>> 	ui->statusBar->showMessage(tr("Loaded %1 rows. Done.").arg(count), 5000) 
> ;
>> }
>>
>> And this is the line I use to try to connect:
>>
>> connect(sqlLoader, SIGNAL(loadEnded(size_t)), this,
>> SLOT(loadComplete(size_t))) ;
>>
>> Both of the applicable headers are MOC processed and both contain the
>> Q_OBJECT macro, which leaves me seriously confused.
>>
>> Can anyone shed some light on this please?
> 
> Probably yes, if you can provide a minimal compilable example that reproduces 
> the problem. In doing so you may even spot the problem yourself.

Hi Sean,

Well needless to say I didn't find anything wrong when creating this 
sample (is it that obvious?), so here it is.

This version uses a const QString & instead of an int but at runtime the 
outcome is the same:

Object::connect: No such slot QPushButton::setText(const QString &) in 
.\sigtest.cpp:9
Object::connect:  (receiver name: 'pushButton')

So to replicate:

Signal Test Sample

sigtest.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
  <class>SigTestClass</class>
  <widget class="QDialog" name="SigTestClass">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>314</width>
     <height>56</height>
    </rect>
   </property>
   <property name="windowTitle">
    <string>SigTest</string>
   </property>
   <widget class="QPushButton" name="pushButton">
    <property name="geometry">
     <rect>
      <x>10</x>
      <y>20</y>
      <width>75</width>
      <height>23</height>
     </rect>
    </property>
    <property name="text">
     <string>Thread</string>
    </property>
   </widget>
   <widget class="QPushButton" name="pushButton_2">
    <property name="geometry">
     <rect>
      <x>230</x>
      <y>20</y>
      <width>75</width>
      <height>23</height>
     </rect>
    </property>
    <property name="text">
     <string>Quit</string>
    </property>
   </widget>
  </widget>
  <layoutdefault spacing="6" margin="11"/>
  <resources>
   <include location="sigtest.qrc"/>
  </resources>
  <connections/>
</ui>

sigtest.h

#ifndef SIGTEST_H
#define SIGTEST_H

#include <QtGui/QDialog>
#include "ui_sigtest.h"
#include "SignalTest.h"

class SigTest : public QDialog
{
	Q_OBJECT

public:
	SigTest(QWidget *parent = 0, Qt::WFlags flags = 0);
	~SigTest() { } ;

private:
	Ui::SigTestClass ui;
	SignalTest * pTest ;
};

#endif // SIGTEST_H

sigtest.cpp

SigTest::SigTest(QWidget *parent, Qt::WFlags flags) : QDialog(parent, flags)
{
	ui.setupUi(this) ;
	ui.pushButton_2->setDefault(true) ;
	pTest = new SignalTest() ;
	connect(ui.pushButton_2, SIGNAL(clicked()), this, SLOT(close())) ;
	if (connect(pTest, SIGNAL(Boo(const QString &)), ui.pushButton, 
SLOT(setText(const QString &))))
	{
		pTest->Start() ;
	}
	else
	{
		ui.pushButton->setText("Oops") ;
	}
}

SignalTest.h

#ifndef _SIGNALTEST_H
#define _SIGNALTEST_H

#include <QObject>
#include <QThread>

class SignalTest : public QThread
{
	Q_OBJECT
public:
	SignalTest() ;
	~SignalTest() { } ;
	void Start() ;
signals:
	void Boo(const QString &) ;
protected:
	void run() ;
	QString msg ;
} ;

#endif

SignalTest.cpp

#include "SignalTest.h"

SignalTest::SignalTest()
{
	msg = "Done" ;
}

void SignalTest::Start()
{
	start() ;
}

void SignalTest::run()
{
	emit Boo(msg) ;
}

main.cpp

#include "sigtest.h"
#include <QtGui/QApplication>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	SigTest w;
	w.show();
	return a.exec();
}