emit signal and recognizing in a different class

[salmanmanekia]

Hi,
I am emitting a signal from A class and anticipating that the connect statemt in the B class connects my signal from A class to the slot function in the B class..
Two ways i understood for this !..
1, If i put an #include A statement in the B,
and/or
2, If B inherits from A,
Please ,if any one can point out which is the right approach or if both are dumb :P and i shud do something else..
Thanks already ...

[Zlatomir]

You don't need to derive or create the objects one into the other, you can also create the objects in the same scope, like:

int main()
{
//...
A objA;
B objB;
QObject::connect(&objA, SIGNAL(boo()), &objB, SLOT(onBooDoSomething()));
//...
}

int main()
{
//...
A objA;
B objB;
QObject::connect(&objA, SIGNAL(boo()), &objB, SLOT(onBooDoSomething()));
//...
}

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Basically you just need to pointers to those objects (and of course you need to make sure that the object "live" in the same time )
Read more here

[salmanmanekia]

it seems that my problem statement wasnt accurate to be properly understood.... i will repeat my question again
i have two classes for eg A and B ..

#include "B"
class A: public QObject
{
..
B bObj;
..
connect (&bObj,SIGNAL(bSignal()), this, SLOT(anyAFunc()));
..
}
------------------------------------------------------------------------
class b: public QWIdget
{
..
emit bSignal();
..
..
}

#include "B"
class A: public QObject
{
..
B bObj;
..
connect (&bObj,SIGNAL(bSignal()), this, SLOT(anyAFunc()));
..
}
------------------------------------------------------------------------
class b: public QWIdget
{
..
emit bSignal();
..
..
}

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Now this techque seems to be a flaw as the compiler complains

Object::connect: No such signal b::bSignal()

[Zlatomir]

Didn't you forgot to declare bSignal with signals: access specifier?

//and... as i said in previous post you don't have to use composition (or inheritance) for signal-slot connection to work.

[salmanmanekia]

the bSignal is declared with the signals access specifier....

[FelixB]

please show the header with the definition of B

[bruceariggs]

#include <QWidget>
 
class b: public QWidget
{
 
    Q_OBJECT
 
    public:
 
    // Public functions here
 
    public slots:
 
    // Public slots here
 
    signals:
 
    void bSignal(); // <-- This is how you declare a signal
 
    protected:
 
    // Protected members here
 
    private:
 
    // Private members here
};

#include <QWidget>

class b: public QWidget
{

    Q_OBJECT

    public:
    
    // Public functions here

    public slots:

    // Public slots here

    signals:

    void bSignal(); // <-- This is how you declare a signal

    protected:

    // Protected members here

    private:

    // Private members here
};

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[salmanmanekia]

B.hpp

#include <QWidget>
#include <QGridLayout>
#include <QLabel>
#include <QToolButton>
#include <QIcon>
#include <QComboBox>
 
namespace UpstreamPrivateNamespace{
 
class B : public QWidget
	{
		Q_OBJECT
 
		public:
			B( QWidget * ParentP = 0 );
 
		signals:
                        .....
			void bSIgnal(const QString&);
 
		public slots:
 
			void bSlot(const QString& );
 
 
		private:
			QIcon * iconVar;
			QComboBox * boxVar;
	};
}

#include <QWidget>
#include <QGridLayout>
#include <QLabel>
#include <QToolButton>
#include <QIcon>
#include <QComboBox>

namespace UpstreamPrivateNamespace{

class B : public QWidget
	{
		Q_OBJECT

		public:
			B( QWidget * ParentP = 0 );

		signals:
                        .....
			void bSIgnal(const QString&);

		public slots:
			
			void bSlot(const QString& );

		
		private:
			QIcon * iconVar;
			QComboBox * boxVar;
	};
}

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B.cpp

b::b( QWidget * ParentP )
	: QWidget( ParentP )
	{
..
                this->boxVar = new QComboBox(this);
		connect(this->boxVar, SIGNAL(currentIndexChanged(const QString& )), this, SLOT(bSlot(const QString& )));
..
}
void b::bSlot(const QString& var)
	{
 
		emit bSignal(var);
 
	}

b::b( QWidget * ParentP )
	: QWidget( ParentP )
	{
..
                this->boxVar = new QComboBox(this);
		connect(this->boxVar, SIGNAL(currentIndexChanged(const QString& )), this, SLOT(bSlot(const QString& )));
..
}
void b::bSlot(const QString& var)
	{

		emit bSignal(var);

	}

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[FelixB]

does bSlot get called when you change the combobox index?

btw, you can connect signals with signals directly:

connect(this->boxVar, SIGNAL(currentIndexChanged(const QString& )), this, SIGNAL(bSignal(const QString& )));

connect(this->boxVar, SIGNAL(currentIndexChanged(const QString& )), this, SIGNAL(bSignal(const QString& )));

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[salmanmanekia]

does bSlot get called when you change the combobox index?

yes

btw, you can connect signals with signals directly:

i remember this now, this is what happens when u do programming after 3 years gap ..

I will also mention the A class ..

A.hpp

..
public slots:
void setDev(const QString &);
private:
B * bObj ;
..

..
public slots:
void setDev(const QString &);
private:
B * bObj ;
..

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A.cpp

constructor
bObj = new b();
connect(bObj, SIGNAL(bSignal(const QString &)), this, SLOT(setDev(const QString &)));
// constructor ends here
 
void setDev(const QString & dev)
{
QLOG_INFO() << dev ;
}

constructor
bObj = new b();
connect(bObj, SIGNAL(bSignal(const QString &)), this, SLOT(setDev(const QString &)));
// constructor ends here

void setDev(const QString & dev)
{
QLOG_INFO() << dev ;
}

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The const was missing from the connect statemet in the Signal ... the 'No such signal ' warning disapears but the connect statement doesnt work ...as the A:setDev function isnt called when the combobox value changes ....

[boudie]

Check your spelling.

void bSIgnal(const QString&);
!=
void bSignal(const QString&);

[salmanmanekia]

Thanks boudie its a typo in the forum .....in the code the spellings are correct !