Signals and Slots - why won't this constellation not work

[FlashMuller]

Hey guys,
I've been working with Qt for a few weeks now, still I can't get this specific Signal/Slot/Constellation running.
I've got a class, "Analytic", which is a QObject (defined in Analytics.h) and has got a SLOT called display(), which is called at the end of another function ( in Analytics.cpp).
Now I've got a Mainwindow (defined in MWindow.h) which has got the public SLOT draw_layer() (defined in MWindow.cpp).
What I additionally do is

Analytics *Analy = new Analytics();
connect(Analy, SIGNAL(display()), this, SLOT(draw_layer()));

this is both happening in the main function of my MWindow.cpp

To sum it up: I've got 4 files -> 2 cpp and 2 h. In Header/File 1 I've got a signal, and in Header/File 2 I've got the public SLOT. Qt doesn't give me an error when compiling or while running, but the SLOT is just not triggered, although it works as a function.
Thanks in advance,
Daniel

[Lykurg]

Show us your code! One guess: did you use the Q_OBJECT macro and did you emit the signal properly?

[CeeKey]

Hey,

your display() Slot has to be a Signal. This Signal musst be emitted if your Event is processed.

[amoswood]

Yeah, I would check that display() slot is defined under as a signal and that you include the Q_OBJECT macro in your class definition and that you emit your signal. (See below)

class Analyic : public QObject
{
  Q_OBJECT
public:
  Analytic();
  void process_something()
  {
    // process something here
    emit signalDisplay();
  }
signals:
  void signalDisplay();
}

class Analyic : public QObject
{
  Q_OBJECT
public:
  Analytic();
  void process_something()
  {
    // process something here
    emit signalDisplay();
  }
signals:
  void signalDisplay();
}

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[Zlatomir]

Most likely you forgot to emit the display() signal... or if you emit it, check your call/connection to the function/slot in witch you emit the signal.

[FlashMuller]

That was display()-thing was a typo. It is a SIGNAL


Here is my code. I'll just post the relevant parts, but you'll habe to live with the fact, that the naming of my files/variables is german:

DGM_Analyse.h:

#ifndef DGM_ANALYSE
#define DGM_ANALYSE
#include "Mainheader.h"
 
class DGM_Analytik:public QObject
{
Q_OBJECT
	public:
		DGM_Analytik(QObject* = 0);
 
	signals:
		void entw_anzeigen();
 
};
#endif

#ifndef DGM_ANALYSE
#define DGM_ANALYSE
#include "Mainheader.h"

class DGM_Analytik:public QObject
{
Q_OBJECT
	public:
		DGM_Analytik(QObject* = 0);
		
	signals:
		void entw_anzeigen();

};
#endif

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---------------------------------
DGM_Analyse.cpp:
Well, a lot of functions in here, so the on line about the signal:

emit entw_anzeigen();

emit entw_anzeigen();

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----------------------------------
Hauptfenster.h: (MainWindow)

#ifndef HAUPTFENSTER_H
#define HAUPTFENSTER_H
 
#include "DGM_Analyse.h"
 
 
 
class Hauptfenster:public QMainWindow
{
	Q_OBJECT
 
	public:
		Hauptfenster();
 
 
	public slots:
                              void Entw_Layer();	
};
#endif

#ifndef HAUPTFENSTER_H
#define HAUPTFENSTER_H

#include "DGM_Analyse.h"



class Hauptfenster:public QMainWindow
{
	Q_OBJECT
	
	public:
		Hauptfenster();
		
	
	public slots:
                              void Entw_Layer();	
};
#endif

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-----------------------------------------
and finally Hauptfenster.cpp:

Hauptfenster::Hauptfenster()
{
 
...
	Analytik = new DGM_Analytik(this);
                connect(Analytik, SIGNAL(entw_anzeigen()), this, SLOT(Entw_Layer()));
...
 
}

Hauptfenster::Hauptfenster()
{

...
	Analytik = new DGM_Analytik(this);
                connect(Analytik, SIGNAL(entw_anzeigen()), this, SLOT(Entw_Layer()));
...

}

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Hope that helped.
Daniel

[CeeKey]

You still have to emit your signal!

[FlashMuller]

Didn't I do so by
"emit entw_anzeigen();"?
in the DGM_Analyse.cpp?

[Zlatomir]

In file DGM_Analyse.cpp, the emit entw_anzeigen(); is within a function or slot (most likely, because you probably need to display() when the user does something... ) so check if the function is called or that slot gets connected (with button click or whatever user action it should be connected with).

[CeeKey]

Didn't I do so by
"emit entw_anzeigen();"?
in the DGM_Analyse.cpp?

Yes, but i can't see in which case you emit this signal. So it looks like you did not call this in the case you would like.

[FlashMuller]

Zlatomir is right,
the emit command is inside a function which is a slot itself. Anyway, this works: The Slot-function is being called, doing its job and then emitting the signal. I did a Step-by-step Debug and when reaching the "emit-command" first the moc-file is being opened

void DGM_Analytik::entw_anzeigen()
{
    QMetaObject::activate(this, &staticMetaObject, 1, 0);
}

void DGM_Analytik::entw_anzeigen()
{
    QMetaObject::activate(this, &staticMetaObject, 1, 0);
}

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and then Qt jumps through the QObject.cpp file. It breaks at this point:

if (!sender->d_func()->isSignalConnected(signal_index))
        return; // nothing connected to these signals, and no spy

if (!sender->d_func()->isSignalConnected(signal_index))
        return; // nothing connected to these signals, and no spy

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which of course tells me that the connection doesn't seem to work, but doesn't really tell me how to fix it.

[amoswood]

In the debug console window, it should state if the connection was made or give an error when the connect() function is called.

[CeeKey]

It looks right for me, so you have to post your whole code, or we can only guess along.

[FlashMuller]

It should :-)
It doesn't give an error while debugging (QObject: No such Slot or Signal) and it doesn't give any feedback when it returns from the QObject.cpp.
Daniel

[FlashMuller]

In the attachment you will find the four files. You don't have a working programm with that, but you can try to catch up with me like that. Hope the variable-names aren't a too big problem.
Thanks

P.S.: Please no comments about the rest of my programming ;-)

[FlashMuller]

Noone got an idea? (in other ords: PUSH )