Minimum required to emit a signal

[davethomaspilot]

I've been using signals and slots with classes derived from classes created in Qt Designer. In addition to inheriting from the class created with Designer, I inherit from QDialog or QWidget (monkey see monkey do).

I dutifully add the Q_OBJECT in the derived class header file, and everything seems work. I can connect signals of built-in widgets to my own custom slots and emit (and connect) my own custom signals. I must confess I don't understand what's going on "under the covers".

I have some utility classes that really aren't GUI oriented. But, I can see it would be handy for some of the methods in these clases to emit signals that could be connected to new widgets I'd create for displaying some diagnostic information.

I think I need the Q_OBJECT in these class declarations to have a signals: keyword

But, what what do should I inherit from? When I tried to public inherit only from QDialog or QWidget, the compiler complains about not being able to access private data in the base class. And that doesn't seem clean, given my derived class is only similar to a QDialog or QWidget in that it would emit a signal.

So, what do I need just to create a signal?

Thanks,

Dave Thomas

[wysota]

But, what what do should I inherit from?

Inherit QObject.

[davethomaspilot]

Thanks for the quick reply.

I get similar error messages when inheriting from QObject:

1>c:\users\dave\my software\stats helper\heat_message.h(127): error C2248: 'QObject:perator =' : cannot access private member declared in class 'QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(333) : see declaration of 'QObject:perator ='
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(112) : see declaration of 'QObject'
1> This diagnostic occurred in the compiler generated function 'HeatMessage &HeatMessage:perator =(const HeatMessage &)'
1> main_window.cpp

1>c:\users\dave\my software\stats helper\heat_message.h(127): error C2248: 'QObject::QObject' : cannot access private member declared in class 'QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(333) : see declaration of 'QObject::QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(112) : see declaration of 'QObject'
1> This diagnostic occurred in the compiler generated function 'HeatMessage::HeatMessage(const HeatMessage &)'
1> moc_collect_stats.cpp
1>c:\users\dave\my software\stats helper\heat_message.h(127): error C2248: 'QObject::QObject' : cannot access private member declared in class 'QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(333) : see declaration of 'QObject::QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(112) : see declaration of 'QObject'
1> This diagnostic occurred in the compiler generated function 'HeatMessage::HeatMessage(const HeatMessage &)'
1> moc_main_window.cpp
1>c:\users\dave\my software\stats helper\heat_message.h(127): error C2248: 'QObject::QObject' : cannot access private member declared in class 'QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(333) : see declaration of 'QObject::QObject'
1> c:\opencv\dep\qt\qt-everywhere-opensource-src-4.8.2\include\qtcore\../../src/corelib/kernel/qobject.h(112) : see declaration of 'QObject'
1> This diagnostic occurred in the compiler generated function 'HeatMessage::HeatMessage(const HeatMessage &)'
1> Generating Code...
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:07.10

It compiles fine without the Q_OBJECT and inheritance from QObject.

Do I need a different constructor that passes 0 to the Bo

Here's the relevant part of header file:

#ifndef HEAT_MESSAGE_H
#define HEAT_MESSAGE_H
 
#include <QtCore/QCoreApplication>
 #include <QRegExp>
 #include <QMap>
#include <iostream>
#include <fstream>
 #include <QTextStream>
#include <QWidget>
 
class HeatMessage : public QObject
{
	Q_OBJECT
 
public:
	HeatMessage(QByteArray &,QObject *parent=0);
	HeatMessage(void);
	QList<HeatRecord> heat_records;
	float get_time(char lane, char id);
	float get_sum_time(char lane);
	char get_result(char lane);
	int get_race(void) {return heat_records.begin()->get_race();};
	int get_heat(void) {return heat_records.begin()->get_heat();};
	int num_dogs(char lane);
	static void print_header(QTextStream &);
	void print(char lane,  QTextStream &);
	void print(QTextStream &);

#ifndef HEAT_MESSAGE_H
#define HEAT_MESSAGE_H

#include <QtCore/QCoreApplication>
 #include <QRegExp>
 #include <QMap>
#include <iostream>
#include <fstream>
 #include <QTextStream>
#include <QWidget>

class HeatMessage : public QObject
{
	Q_OBJECT

public:
	HeatMessage(QByteArray &,QObject *parent=0);
	HeatMessage(void);
	QList<HeatRecord> heat_records;
	float get_time(char lane, char id);
	float get_sum_time(char lane);
	char get_result(char lane);
	int get_race(void) {return heat_records.begin()->get_race();};
	int get_heat(void) {return heat_records.begin()->get_heat();};
	int num_dogs(char lane);
	static void print_header(QTextStream &);
	void print(char lane,  QTextStream &);
	void print(QTextStream &);

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};
#endif

[ChrisW67]

The QObject copy and assignment constructors are declared private. You cannot copy a QObject and will get these sort of errors if you attempt to do that.

[wysota]

You can't create copies or assignments to QObject instances. You probably have an assignment operator in your class (or the compiler tries to create one for you based on your code). This is not possible.

[davethomaspilot]

Hmm, I don't see anthing like that, unless the following fragment (which is called from a method in a different QWidget class)

HeatMessage hm(msg);
emit new_heat(hm);

HeatMessage hm(msg);
emit new_heat(hm);

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Do you have a suggestion on how to find the offending code?

Thanks,

Dave Thomas

[wysota]

What is in heat_message.h file in line 127 (and around)?

[davethomaspilot]

That's the last line in the header file (the }

Not very useful.

[code]

void print(char lane, QTextStream &);
void print(QTextStream &);



line 127: };

[wysota]

Please post the whole file as an attachment.