Signal Slot connection from different classes

[rokemoon]

You need that Class_B inherited QObject or derived from it, then add macro Q_OBJECT:
@class Class_B: public QObject
{
Q_OBJECT
private:
void aMethod();

signals:
void trigger_Do_Some(int, int);
};@
and in "connect":http://doc.qt.nokia.com/latest/qobject.html#connect use pointers.

[aamer4yu]

You need Q_OBJECT declaration in class B.. isnt it ?

[huckfinn]

Not really, I just added Q_OBJECT, but I have the same error.
class Class_B : public QThread, public QObject, also the same error.

Then I added via Singleton:
@
const Class_B * pCB = ref2ClassB.GetInstance();
connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
@

Now I can compile, but therefore LNK2001 and LNK2019 link errors.

[huckfinn]

Ok, LNK2001 gone, when I removed Q_OBJECT from Class_B. I only let Class_B : public QThread, public QObject

[aamer4yu]

Just use
class Class_B : public QThread

QThread is already inherited from QObject.
Does it work ?

[rokemoon]

QThread inherits from QObject, so class Class_B : public QThread -,public QObject-

[huckfinn]

Ok, removed.

@
const Class_B * pCB = ref2ClassB.GetInstance();
/// error C2594: 'argument' : ambiguous conversions from 'const Class_B *' to 'const QObject *'
connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
/// error C2664: 'bool QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)' : cannot convert parameter 1 from 'Class_B' to 'const QObject *'
1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
connect( ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
@

[rokemoon]

[quote]
All classes that contain signals or slots must mention Q_OBJECT at the top of their declaration. They must also derive (directly or indirectly) from QObject.
[/quote] from "here":http://doc.qt.nokia.com/4.7/signalsandslots.html

const Class_B * pCB = ref2ClassB.GetInstance();
// here the Class_B must inherit from QOBject
connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );

// here you need the pointer
connect( &ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );

[huckfinn]

[quote author="rokemoon" date="1313050079"]
// here you need the pointer
connect( &ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
[/quote]

This way I get an error C2594: 'argument' : ambiguous conversions from 'Class_B *' to 'const QObject *'

[rokemoon]

Class_B must inherite QObject (directly or indirectly), can you give us latest code of your Class_B?

[huckfinn]

Latest Class_B:
@
#include <QtCore/QThread>

template class SWITCHEXPORT QMap< int, QString >;

class Class_A;
class QModelIndex;

class SWITCHEXPORT Class_B : public QThread {
Q_OBJECT

public:
/// @brief Constructor
Class_B( void );

void aMethod();

signal:
void trigger_Do_Some(int, int);

private:
QMap< int, QString > categoryNameByID;
}
@

[rokemoon]

Can you tell us why you use QThread? Can you try inherite from QObject and tell us about result?

[huckfinn]

There is a @QThread::start();@ in the source .cpp .

So when I inherit from both @clas.s Class_B : public QThread, public QObject@ and I am able to compile it.

But now I have linking errors:
@
3>Linking...
3> Creating library C:\MyProject\Debug\MyProject.lib and object C:\MyProject\Debug\MyProject.exp
3>Class_B.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
3>Class_A.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
3>Class_3.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __thiscall Class_B::metaObject(void)const " (?metaObject@Class_B@@UBEPBUQMetaObject@@XZ)
3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual void * __thiscall Class_B::qt_metacast(char const *)" (?qt_metacast@Class_B@@UAEPAXPBD@Z)
3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall Class_B::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@Class_B@@UAEHW4Call@QMetaObject@@HPAPAX@Z)
3>Class_B.obj : error LNK2019: unresolved external symbol "protected: void __thiscall Class_B::trigger_Do_Some(long,long)" (?trigger_Do_Some@Class_B@@IAEXJJ@Z) referenced in function "public: virtual void __thiscall Class_B::HandleMessage(void * const)" (?HandleMessage@Class_B@@UAEXQAX@Z)
3>C:\MyProject\Debug\MyProject.dll : fatal error LNK1120: 5 unresolved externals
@

[mrtc3]

When you have added Q_OBJECT to Class_B.h recently, then assure yourself that moc_ClassB.cxx has been generated as well.
If that is the case, this moc-file should be listed in the .pro or .vcpro file as Source
e.g.:
@
<Files>
<Filter Name="Source Files">
<File RelativePath="C:\path\moc_Class_B.cxx">
</File>
<!-- ....etc...-->
@

[huckfinn]

I added these tags to the vcpro file, now I can compile and run my application.

However, now I have a
@
warning C4584: 'Class_B' : base-class 'QObject' is already a base-class of 'OtherClass'
@

I dont like warnings :(

[loladiro]

Multiple inheritance is NOT supported for QObject based classes. Can you change your code?

[Ramin7000]

main.cpp :
@
#include <QtGui>
#include <converter.h>

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

QGraphicsScene scene(0,0,500,300);
QGraphicsView view(&scene);

QLabel *l = new QLabel();
QSlider *s = new QSlider();

l->setText("Move the slider handle");
s->setOrientation(Qt::Horizontal);

l->setGeometry(100,100,150,50);
s->setGeometry(100,200,150,50);

Converter *ms = new Converter(s,l);


scene.addWidget(l);
scene.addWidget(s);

view.show();
return app.exec();

}@

converter.cpp :
@
#include "converter.h"

Converter::Converter(QSlider *s, QLabel *l)
{
connect(s,SIGNAL(valueChanged(int)),this,SLOT(Changer(int)));
connect(this,SIGNAL(Changer(QString)),l,SLOT(setText(QString)));
}

void Converter::Changer(int x)
{
Changer(QString::number(x));
}
@

converter.h :
@
#ifndef CONVERTER_H
#define CONVERTER_H

#include <QtGui>

class Converter : public QObject
{
Q_OBJECT

public:
Converter(QSlider*,QLabel*);

protected slots:
void Changer(int);

signals:
void Changer(QString);

};

#endif // CONVERTER_H
@

[Edit: Please use @ tags around code. I have added them here. -- mlong]

[vittalonline]

Use Q_PROPERTY for passing arguments in Class-B